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The Shuiyindong gold mine in Guizhou is used as a case study in this paper to study patterns of dust pollution occurring with traditional electric-rake operation. In particular, the study uses the northern quarry of the twenty-third line in the first middle section of the second mining area and establishes a three-dimensional simulation model of equal size. It uses Computational Fluid Dynamics (CFD) to simulate and analyse the airflow traces and distribution of dust concentration in the relevant roadway during each stage of the electric-rake operation. The simulation results show that the airflow in the working roadway has a spiral movement and produces reverse dirty-wind circulation towards the end. Dust flows out of the working roadway from the 8th second of operation, and dust concentration reaches a peak in the working roadway at the 12th second of operation at an average dust concentration of 37.5 mg/m³. The dust concentration drops rapidly from the 120th second and reaches the maximum dust concentration permitted for operation at the 180th second of operation. The validity of the simulation is tested by comparing the actual measured data at the site with the simulation results. Finally, the simulation results are analysed using violent Python, and the solution is used to divide the roadway into areas according to the human breathing range. The paper analyses the distribution of dust concentration at an average human breathing height, providing an established theoretical basis for dust-control work in mines. [Display omitted] [ABSTRACT FROM AUTHOR]

Explosion is a significant threat to chemical process safety, which often occurs suddenly with a wide range of impact, resulting in catastrophic disasters. Predictions of explosion hazards are required for regional safety assessment and disaster resilience enhancement of chemical industrial parks (CIPs). This paper, therefore, aims to develop a conceptual framework for systematically analyzing explosion evolutions and quantifying the potential hazards by combining system-theoretic process analysis (STPA) method with numerical simulation. The proposed framework consists of 5 steps: (i) establishment of hierarchical safe control structures (SCSs) of important chemical processing zones in the CIP, (ii) computational fluid dynamics (CFD) modeling for potential explosion evolutions in each zone by changing the examined parameters randomly, (iii) development of a convolutional neural network (CNN) prediction model through constant self-learning of CFD pressure field data, (iv) comprehensive assessment of blast damage by incorporating the outputs of the above numerical models into existing evaluation methods, (v) identification of unsafety control actions and causes, and safety constraints for the improvement of SCSs. Provided with monitoring data, the developed analysis architecture can predict explosion process hazards and recommend appropriate safety strategies in real time. This would service the multi-level requirements for explosion prevention and protection, supporting better-informed decision-making. The paper describes the concepts and implementation process of the method as a first step. [ABSTRACT FROM AUTHOR]

IVR-ERVC (In-Vessel Retention – External Reactor Vessel Cooling) is a critical accident management method for ensuring the integrity of the reactor pressure vessel (RPV) lower head. One of the most crucial aspects within this method is to enhance the CHF (Critical Heat Flux) on the outer surface of the reactor pressure vessel (RPV) lower head. This paper explores the application of graphene nanofluids in IVR-ERVC. This paper uses computational fluid dynamics to numerically simulate the CHF characteristics of graphene nanofluids under different undercooling, mass flow rate, concentration, tilt angle, and gap size conditions and analyzes the impact of different factors on CHF and the coupling effects between different factors. The undercooling range is 5 K–100 K, the mass flow rate range is 150 k g / (m 2 ∙ s) to 3000 k g / (m 2 ∙ s) , the concentration range is 0–1%, the inclination angle range is 0°–90°, and the gap sizes are 10 mm and 20 mm. The results show that the CHF can be effectively improved by adding nano-graphene into the base solution, and the CHF increases with the increase of subcooling degree, mass flow rate, concentration, dip Angle and gap size. Within the simulation range, the strengthening effect on CHF weakens when raising the undercooling and mass flow rate. And the larger the concentration and inclination angle within the simulation range, the better the enhancement effect on CHF. The maximum increase was 290%, while the average increase was 75.6%. This article studies the coupling effects between different parameters through numerical simulation. It can be concluded that increasing the mass flow rate weakens the enhancement of subcooling and concentration on CHF, increasing the subcooling weakens the enhancement effect of mass flow rate and concentration on CHF, and increasing the concentration enhances the enhancement effect of subcooling and mass flow rate on CHF. Enhance the mass flow rate will weaken tilt angle effect, while increasing the concentration will enhance the strengthening effect of tilt angle on CHF. [ABSTRACT FROM AUTHOR]

With the large-scale application of polymer flooding technology, the polymer concentration in produced water is increasing, which leads to incomplete regeneration of filter media by gravity field hydraulic backwashing technology only. In this study, the high-gravity backwashing technology is constructed by coupling gravity field and swirl field, which promotes the development of the oilfield. Based on the cascade theory, this paper establishes a mathematical expression of radial collision force in the high-gravity backwashing process in the vortex tube and solves a mathematical equation of high-gravity backwashing velocity gradient G based on the efficient zone of collision force action. Meanwhile, based on the discrete element method and computational fluid dynamics theory, the inter-particle collision regulation of the high-gravity backwashing process is simulated by the coupled FLUENT-EDEM method, and the high-efficiency zone of the backwashing process is verified. In this high-efficiency zone, the theoretical and simulated values of velocity gradient G for different high-gravity values match well, with differences ranging from –5.8 % to +7.1 %, indicating that the theoretical model of high-gravity backwashing is correct. When the high-gravity value is 210–240 g, the total impulse of the filter bed per unit time reaches a great value, and the backwashing velocity gradient G is 3047.1 s−1, which is much larger than the G value of combined air-water backwashing. The high-gravity backwashing technology breaks through the technical bottleneck of low efficiency in the action of the gravity field. It enriches and develops the gravity field hydraulic backwashing technology of the filter bed. • A new method of high-gravity backwashing is proposed, and a theoretical model of high-gravity backwashing is constructed. • The mathematical equations particle impact force and velocity gradient in high efficiency area of high-gravity backwashing are established. • The coupling method of FLUENT-EDEM is used to study the backwashing process, which provides a new idea for the backwashing of traditional water treatment filter bed. [ABSTRACT FROM AUTHOR]

As a mesh-free approach, the incompressible Smoothed Particle Hydrodynamics (ISPH) method has been often used for simulating wave-structure interaction problems. In the conventional ISPH method, the pressure-projection phase of solving the pressure Poisson's equation (PPE) is the most time-consuming. In recent years, the machine learning (ML) techniques has gradually shown their potential in accelerating the computational fluid dynamics. In this paper, the graph neural network (GNN) supported ISPH method (ISPH_GNN), in which the GNN replaces solving the PPE for the fluid pressure in the conventional ISPH, is adopted for numerical simulations of wave-floater interactions. To the best of the authors' knowledge, this is the first work to study the wave-floater interactions by using GNN supported ISPH method. More importantly, this paper demonstrates that the GNN trained only on data for simpler wave-only cases (i.e. no structure in the wave fields) can be satisfactorily applied to the cases for wave-floater interactions. More specifically, the paper will show this by using the ISPH_GNN with such trained GNN model to simulate various different cases, including the decay tests of a box, a floating box subjected to a wave, the interaction between wave and a moored floating breakwater and the violent green water impact on a floating structure. In most of the cases, the numerical results are validated by comparing with experimental data. Agreement between them is surprisingly satisfactory, being as good as those obtained by the conventional ISPH. The paper will also show that the ISPH_GNN requires much less computational time (97 times less for the cases concerned) than the conventional ISPH for estimating pressure involved in wave-floater interactions. This reveals a great potential that one can train the GNN using the datasets for simpler cases and then use the ISPH_GNN to simulate wave-floater interaction problems. • The first work to study the wave-floater interactions by using the graph neural network (GNN) supported ISPH method. • The GNN trained only on data for simpler wave-only cases can be applied to more complex cases for wave-floater interactions. • The ISPH_GNN can give satisfactory results for the relatively complex cases involving wave-floater interactions. • The ISPH_GNN takes much less computation time than the conventional ISPH for estimating pressure. [ABSTRACT FROM AUTHOR]

In this paper, computational fluid dynamics (CFD) numerical simulation is used to analyze and discuss the horizontal propagation process of premixed hydrogen flame with obstacles. A total of three different obstacle channel arrangements at the blocking ratio of 0.5, which will affect the explosion flame and pressure development. The results show that the premixed flame is affected by flow instabilities and vortices when propagating through the obstacle channel, thereby distorting the flame. The vortices outside the flame boundary are more conducive to the acceleration of the flame. The continuous acceleration and synergistic promotion of the flame is more prominent due to the existence of the channel in the central axis of flame propagation, and the maximum velocity even achieved 307.91 m/s. The degree of the wrinkle of flame increases with the number of obstacle channels. The flame propagation process is always accompanied by pressure variations, and the dynamic pressure builds up at the flame front and intensifies periodically. But the downstream pressure gradually increases as the number of obstacle channels increases. CFD simulation of the explosion process clearly reveals the changing trends and interactions of explosion characteristic factors. • The vortex outside the flame boundary is more beneficial for flame acceleration. • Arrangement of obstacle channels effects the trend of flame front motion. • Pressure oscillation and magnitude can be changed by the obstacle arrangement. [ABSTRACT FROM AUTHOR]

Abstract The ventilation effect in different places in the teaching building is different. The aim of this paper is to study the relative ventilation relationship of the rooms in "line" type middle school teaching building. Taking Xiamen in the subtropical region as a typical city, a number of parameters such as the inside and outside corridors, different room sizes and different ventilation angles were set as variables, using the CFD simulation method. Combined and separated effects of the defined parameters on natural ventilation performance are evaluated using the ratio of air-age area as criteria. The result shows that the "line" type teaching building with outside corridor ventilation is 35.55% better than the inside corridor. In addition, the ventilation in large room is 30.84% better than that in small rooms. In 0°–35° wind direction, the closer the room to the incident wind the better in ventilation, but in a certain angle range of 59°–90°, the room farther away from the incident wind, the better in ventilation. The best wind angle of "line" teaching building ventilation is 305°–55°. The research results in this paper can help architects to design buildings more scientifically and reasonably. Highlights • "Line" type teaching building should adopt outside corridor form, it is conducive to ventilation in subtropical area. • The outside corridor ventilation effect is 35.55% better than the inside corridor. • Large room is suitable for laboratory and small room is suitable for temporary lounge cause ventilation feature. • The ventilation effect of the classrooms is related to the wind direction and classroom positions. [ABSTRACT FROM AUTHOR]

A wave-driven unmanned surface vehicle (WUSV) can sail on the sea simply by utilizing wave energy as its driving power. Recently, many studies have been performed on practical applications of oceanic scientific exploration by a WUSV, where the estimation criterion of the navigation performance of the WUSV is always its sailing velocity, although this method is very intuitive but not effective in analyzing the shortcomings in the design of the WUSV. On this basis, a new estimation method, which focuses on the efficiency of utilizing wave energy by the WUSV, is proposed in this paper. The theoretical contribution of this paper is that a generalized solution function for the efficiency of utilizing wave energy is obtained and is expressed in the form of the product of several non-dimensional parameters. In detail, algorithms to calculate input power, i.e., wave energy harvested by the surface float, and usable power, i.e., the product of sailing velocity and thrust force, have been developed. The other development presented in this paper is the proposal of some effective ways to improve the ability of the WUSV to utilize wave energy. Then, numerical simulations are carried out to validate the proposed method, and corresponding experiments are employed to investigate the performance of the method. The results show that the four major factors to impact the ability of the WUSV utilize wave energy are the thrust force of the propulsor, the sailing velocity of the WUSV, the principal dimensions of structures and the wave environment parameters. Summarizing the analysis in numerical validations and experimental studies, the WUSV can generally achieve higher efficiency in utilizing wave energy when it sails in a specific wave environment with certain parameters. Meanwhile, the utilization efficiency of the WUSV is not always much higher, and the reasons for this phenomenon mainly include two aspects: (1) most of the wave energy harvested by the surface float is used to work against the calm water resistance of the propulsor and the umbilical cable; and (2) based on the current design, the motions of the surface float cannot fully respond to the waves. Therefore, an integrated optimizing design for the propulsive and resistance performance of the propulsor, as well as the motion response and resistance performance of the float, will be an effective way to improve the ability of the WUSV to utilize wave energy. In addition, the differences in the sailing velocity and heaving amplitude of foils cause different curve trends for the utilizing efficiency between numerical simulations and experiments. [ABSTRACT FROM AUTHOR]

In response to the optimization problem of the motion law of the pectoral fins of biomimetic robotic fish, this paper uses computational fluid dynamics (CFD) methods to achieve the CFD optimization of two types of rigid biomimetic pectoral fins with three degrees of freedom (DOF): elliptical and 8-shaped swing curves. By analyzing the hydrodynamic characteristic curve of the pectoral fins, pressure distribution upstream and downstream of the fin surface, velocity vector of the surrounding flow field during pectoral fin swing, and three-dimensional vortex structure, it is found that when the pectoral fins are pushed forward in an elliptical swing curve, the resistance peak value decreases after two optimizations. However, at the same time, a certain amount of thrust is lost. When the pectoral fin advances in an 8-shaped swinging curve, after two optimizations, the pectoral fins resistance decreases while maintaining an enormous thrust, comprehensively improving the propulsive effect of the pectoral fin on the robotic fish. By substituting the optimized 8-shaped pattern into the robotic fish model, it is found that the flapping angle of 35 ° has better drag reduction performance, and the average swimming speed of the robotic fish is the fastest at this angle. • After secondary optimization, the elliptical pectoral fin swing curve with better drag reduction performance and smoother curve was obtained • Optimize the 8-shaped swing curve to comprehensively enhance the propulsion effect of pectoral fins on robotic fish • Substituting the optimized 8-shaped swing pattern into the robotic fish model to achieve self-propelled motion, it was found that p h i F L A = 35 d e g r e e had the best performance [ABSTRACT FROM AUTHOR]

Empirical validation and code-to-code comparison of more than one building simulation tool has seldom been done in literature. Therefore this paper presents the first detailed comparison of 1D building energy simulation tools with 3D CFD simulation and measurement data from a test bed (Test-Box), exposed to natural environmental conditions. Dymola (library: IDEAS), EnergyPlus, IDA ICE and TRNSYS –four commonly used tools– were selected for comparison against highly accurate real measurement data and dynamic CFD results. This paper evaluates the performance of mentioned above 1D simulation tools and in particular their implemented Thermally Activated Building Systems (TABS) models. The mean error, RMSE, standard deviation and maximal error for the room air, the ceiling surface and concrete temperature of the Test-Box model results are acceptable for all tools. The time course of the room air temperature follows the measurement data relatively well for all four tools. However, the negative bias (Dymola -0.92 K, EnergyPlus -2.18 K, IDA ICE -0.37 K and TRNSYS -1.13 K) indicates a general overestimation for all tools. Furthermore, the paper reflects the properties of simulation tools regarding the modelling language, GUIs, co-simulation capabilities and their recommended field of application. [ABSTRACT FROM AUTHOR]

A central issue in hydraulic fracturing treatment in petroleum wells is the transport of proppant particles by the injection fluid. In this paper, we present an innovative proppant transport model in a fixed rectangular- and elliptic-shaped slots. The proposed model is an improvement to the current modeling of proppant transport by applying a non-oscillatory numerical scheme which has high accuracy everywhere in solution domain, even close to the steep gradients. In addition, inertia, fracture wall, and concentration effects on proppant settling along with slurry evolution as a function of proppant concentration has been considered. This paper introduces the mathematical equations that govern the proppant transport phenomenon and discusses special front capturing numerical techniques, boundary conditions, coupling between proppant and slurry mass conservation equations and time stepping restrictions required for the solution stability. We incorporated published correlations obtained from proppant transport laboratory experiments in our numerical model to better capture the physics of the problem. 5 th - order WENO scheme was used to avoid oscillation and diffusion at the proppant front since traditional finite difference discretization was found to be insufficient in solving the hyperbolic transport partial differential equations. Results show that the technique used in this study can capture the proppant distribution with minimum oscillation and diffusion. A series of sensitivity analysis was conducted to explore the legitimacy of these assumptions and to provide guidelines that allow more accurate predictions of the proppant and fluid transfer. Numerical results are presented to show how proppant distribution is impacted by the injection fluid viscosity, density difference between proppant particles and injection fluid, proppant size, and fluid flow injection rate. Results of the sensitivity analysis illustrate the significance of choosing appropriate viscosity of the injection fluid as small changes in the viscosity may cause noticeable effects on the concentration distribution. In addition, we found that variation of proppant size and density within a reasonable range have a modest effect on proppant concentration distribution. Furthermore, we also investigated the amount of gravity driven vertical motion of proppant which is driven by density differences (convection) and compare it to a second gravity driven motion which is proppant settlement. Both of these two well recognized mechanisms can occur inside a fracture during proppant placement, however, the importance of each mechanism as a function of proppant injection design parameters is not fully understood. [ABSTRACT FROM AUTHOR]

The aim of this paper is to study the spray cooling heat transfer characteristics using CFD method. The two phase mathematical model is established based on Euler-Lagrange approach. In this model, unsteady-state flow conditions are simulated. Heat and mass transfer between the vapor and the water droplet are computed. The averaged error of numerical results is 10% compared to experimental results in our previous papers. It is concluded that the heat flux and its distribution on heated surface are influenced by the heated surface temperature, mass flux, nozzle to surface distance and the number of nozzles. Furthermore, the heat flux distribution do not change obviously with the increasing of heated surface temperature, and the heat flux increases with the increasing of mass flux. Moreover, there is an optimal nozzle to surface distance while the spray impingement zone circumscribes in heated surface, and more nozzles lead to higher heat flux and better heat flux distribution on heated surface. Considering the disadvantage of manufacture difficulty and cost increase for more nozzles, there is an optimal nozzle number in certain space and heat dissipation requirement. The optimal number of nozzles is 8 in this article. [ABSTRACT FROM AUTHOR]

The paper presents a comprehensive set of numerical simulations performed to examine the current Computational Fluid Dynamics (CFD) capabilities in the prediction of the interaction of a water mist spray with a vertical upward jet of hot air within an Eulerian-Lagrangian framework. The experimental tests considered herein are described by Zhou [Proceedings of the Combustion Institute, 2015]. The spray is a 30° full cone water mist spray emerging from a nozzle that delivers a water flow rate of 0.084 lpm at a pressure of 750 kPa. The vertical jet of hot air at 205 ∘ C is issued from a 72 mm-diameter nozzle placed at 560 mm below the water spray nozzle. Three exit velocities of 3.3, 4.2 and 5.3 m/s were examined. Gas phase simulations (described in the companion paper, Part I) have allowed to determine a set of parameters (e.g., cell size of 4 mm and modified Deardorff model for the turbulent viscosity) that are suitable for the water mist spray simulations. Moreover, it is shown here that a prescribed complex spray pattern with a full discharge angle of 60° is required in order to match water spray profiles in the nozzle near-field. The three regimes of spray-jet interaction (i.e., water spray dominated, vertical jet dominated or equal influence of the spray and the vertical jet) are qualitatively well captured by the numerical simulations. However, the location of the interaction boundary is underestimated by up to 26%. This could be partially attributed to modelling aspects related to, for example, turbulent dispersion or turbulence inflow conditions of the droplets. Uncertainties in the experimental measurements must also be considered. [ABSTRACT FROM AUTHOR]

The limiting factor for the employment of advanced 3D CFD tools in the analysis and design of rotary vane machines is the unavailability of methods for generation of a computational grid suitable for fast and reliable numerical analysis. The paper addresses this issue through an analytical grid generation based on the user defined nodal displacement which discretizes the moving and deforming fluid domain of the sliding vane machine and ensures conservation of intrinsic quantities by maintaining the cell connectivity and structure. Mesh boundaries are defined as parametric curves generated using trigonometrical modelling of the axial cross section of the machine while the distribution of computational nodes is performed using algebraic algorithms with transfinite interpolation, post orthogonalisation and smoothing. Algebraic control functions are introduced for distribution of nodes on the rotor and casing boundaries in order to achieve good grid quality in terms of cell size and expansion. For testing of generated grids, single phase simulations of an industrial air rotary vane compressor are solved by use of commercial CFD solvers FLUENT and CFX. This paper presents implementation of the mesh motion algorithm, stability and robustness experienced with the solvers when working with highly deforming grids and the obtained flow results. [ABSTRACT FROM AUTHOR]

Efficient cooling system is an essential part of heavy duty extrusion pelleting line which plays an important role in 300 kt/a production engineering of polyolefin. In this paper, a wickless gravity-assisted two-phase cooling system (WGATPCS) used in heavy duty extrusion pelleting line was presented. The volume of the fluid (VOF) model in FLUENT was used to simulate the two-phase flow and heat transfer characteristic during the operation of WGATPCS by solving the equations of continuity, momentum and energy. The vapor velocity and temperature distribution of cooling system were obtained. The operating conditions applied in this paper are the followings: the filling ratio is 0.3, cooling water flow rate is 180 L/h, and heating power is 11 kW. The predicted temperature profile showed a good agreement with experimental data and the maximum relative error was below 0.99%. Therefore, it was concluded that the CFD model successfully reproduced the heat and mass transfer processes in proposed cooling system. The variation of liquid film thickness, the characteristics of liquid film and vapor-liquid interface were also analyzed. The maximum liquid film thickness was 0.017 mm at the bottom of condenser pipe, the velocity of vapor and liquid at vapor-liquid interface were 0.00785 m/s and 0.09 m/s respectively. The average condensation and evaporation heat transfer coefficients were 68083 W/(m 2 K) and 3929 W/(m 2 K), respectively. [ABSTRACT FROM AUTHOR]

In urban areas, vertical axis wind turbines have been installed on both sides of the road and rooftop. Compared with rooftop, vertical axis wind turbines mounted on the side of a building have a larger swept area with longer blades, and the effect of tip vortices can be reduced at the same time. Around the building, there are several high wind speed regions that can provide more wind energy. In this paper, a high-resolution numerical method composed of overset grid and adaptive mesh refinement techniques is adopted to verify the feasibility of vertical axis wind turbines mounted on the side of the building. Firstly, the complex flow field around the building is simplified into the flow field around the cylindrical building. Five typical flow regions with different flow conditions are determined: windward zone, crosswind zone, tailwind zone, recirculation zone and leeward zone. Secondly, wind turbines are installed evenly around the building. The simulation results show that the energy output of wind turbines in tailwind zone can be increased by 120 % compared with the reference value. Thirdly, multiple wind turbines are coupled with the building. In order to get the optimal arrangement, power outputs of four arrangements are compared for the best choice. The results indicate that the arrangement with six wind turbines in crosswind zone and tailwind zone can achieve the best performance. Through changing the rotational directions, the forward blades of wind turbines can be close to the wall, and the energy output of all the wind turbines around the building can be improved. [Display omitted] • The feasibility of wind turbine installation around a single building is verified. • Adaptive mesh refinement method is implemented for simulating several wind turbines' flow physics. • The best installation location around the building is obtained by the comparison of time-averaged power coefficients. • The arrangements method of several wind turbines is discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • The application of numerical simulation in tablet preparation is reviewed. • Most models, i.e., CFD, DEM, PBM, FEM, LBM and MC, are summarized. • The application and deficiencies of these models in tableting are discussed. • It provides a systematic reference for the control and analysis of tableting. Recently, there has been an increase in the use of numerical simulation technology in pharmaceutical preparation processes. Numerical simulation can contribute to a better understanding of processes, reduce experimental costs, optimize preparation processes, and improve product quality. The intermediate material of most dosage forms is powder or granules, especially in the case of solid preparations. The macroscopic behavior of particle materials is controlled by the interactions of individual particles with each other and surrounding fluids. Therefore, it is very important to analyze and control the microscopic details of the preparation process for solid preparations. Since tablets are one of the most widely used oral solid preparations, and the preparation process is relatively complex and involves numerous units of operation, it is especially important to analyze and control the tablet production process. The present paper discusses recent advances in numerical simulation technology for the preparation of tablets, including drying, mixing, granulation, tableting, and coating. It covers computational fluid dynamics (CFD), discrete element method (DEM), population balance model (PBM), finite element method (FEM), Lattice-Boltzmann model (LBM), and Monte Carlo model (MC). The application and deficiencies of these models in tablet preparation unit operations are discussed. Furthermore, the paper provides a systematic reference for the control and analysis of the tablet preparation process and provides insight into the future direction of numerical simulation technology in the pharmaceutical industry. [ABSTRACT FROM AUTHOR]

In order to explore the core corrosion characteristics of horizontal lead-bismuth reactor in oxygen-controlled environment, a liquid lead-bismuth eutectic (LBE) corrosion model including the growth and removal process of oxide layer was established in this paper. The coupling method of double-layered oxidation model and computational fluid dynamics (CFD) was used to simulate the long-term oxidation corrosion of horizontal LBE reactor core numerically. The results show that the average total oxide layer thickness of fuel rod surface is 1.59 μm, and the thickest oxide layer is 3.48 μm on the fuel rod surface at the core outlet after 20,000 h. The fuel rods maintain a double-layer oxide layer structure. The growth rate and removal rate of the oxide layer on fuel rod surface increase with the increase of inlet temperature and the decrease of inlet flow rate. The growth rate of the oxide layer on fuel rod surface increases with the increase of inlet oxygen concentration, while the removal rate decreases. At higher temperature above 420℃, lower flow velocity below 0.25 m/s and lower oxygen concentration below 2 × 10−8wt%, the magnetite layer will first be completely removed from the surface of the fuel rods at the core outlet. The liquid LBE oxidation corrosion model and coupled CFD method presented in this paper can be used for numerical simulation of oxidation corrosion in different units of LBE cooling system. [ABSTRACT FROM AUTHOR]

• Multiphysics framework to study submillimeter sized hydrogen evolution is presented. • Considers bubble growth due to both interfacial mass transfer and coalescence. • Detached bubble is observed to undergo surface oscillations. • Impact of bubble evolution on the current is investigated. • Coalescence seems to drive bubble detachment for continuum length scales. One of the important aspects in improving the efficiency of electrochemical processes, such as water electrolysis, is the efficient removal of bubbles which evolve from the electrodes. Numerical modelling based on Computational Fluid Dynamics (CFD) can describe the process, provide insights into its complexity, elucidate the underlying mechanisms of how bubbles evolve and their effect as well as aid in developing strategies to reduce the impact of the bubble. In this paper, a Volume of Fluid (VOF) based simulation framework to study the evolution of hydrogen bubbles in the order of few hundred micrometers, refered to as continuum scale bubbles, is proposed. The framework accounts for the multiphase nature of the process, electrochemical reactions, dissolved gas transport, charge transport, interfacial mass transfer and associated bubble growth. The proposed solver is verified, for two-dimensional cases, by comparison to analytical solution of bubble growth in supersaturated solutions, stationary bubble, rising bubbles and qualitative analysis based on experimental observations of the variations in current based on static simulations. The proposed solver is used to simulate the evolution of a single bubble under various wetting conditions of the electrode as well as the coalescence driven evolution of two bubbles. The results show that as the bubbles detach, its surface oscillates and the shape of the rising bubble is determined by the balance between drag force and surface tension. These surface oscillations, which causes the bubble to get flattened and elongated, results in temporal variation of the electrical current. The reduction of current due to bubble growth is visible only when these surface oscillations have reduced. The simulations also show the current as a function of the position of the bubble in the interelectrode gap. The framework also predicts the increase in current as a result of bubbles leaving the surface which is larger when the process is coalescence driven. The simulations indicate that bubble coalescence is the underlying mechanism for continuum scale bubble detachment. [ABSTRACT FROM AUTHOR]

This paper describes the design, micro-fabrication and testing of a novel Micro-Aerial Vehicle (MAV) that mimicking a real locust. Actual parameters of locust insect are used to create a micro-scale MAV that can replace the traditional types that mimicking dragonfly and birds. Based on the obtained results, the novel MAV crucial parameters are its weight and strength to take-off under normal locust performance parameters fashion. Computational Fluid Dynamics (CFD) simulations are carried out at angles of attack of 10°, 20° and 30° and flapping frequencies of 19 Hz, 24 Hz, 30 Hz, 35 Hz and 40 Hz to investigate the aerodynamic performance of this designed MAV and optimize its flapping frequency. The simulation results defined the frequency at which the MAV is capable of hovering and take-off. In addition, the simulation results showed that the MAV is able to utilize some lift enhancement mechanisms that are being actually used by insects. These results enhances the manufacturing process of future MAV's, especially in the material selection and manufacturing method, and the transmission mechanism for flight. [ABSTRACT FROM AUTHOR]

• A fluid-like solver is implemented in OpenFOAM to simulate hyperelastic deformations of a weakly compressible material. • Three benchmark cases including torsion, pressing, and bending for 2-D and 3-D geometries are successfully simulated. • At traction boundaries, applying pressure condition deduced from the conservation of mass gives promising results. • Some simplified constitutive laws violate the compatibility between pressure, density and stress. • Compared to Lagrangian, Eulerian approach has computational merits in the case of pure rotation of a cylinder. Unification of the numerical models and methods in computational solid and fluid dynamics has been a research objective with at least two major advantages in mind. The first benefit of such unification is the more efficient data transfer between fluid and solid media, and the second advantage is the possibility of developing a better solver as compared to the separate existing solid and fluid solvers. In this paper, a conservative fluid-like pressure-velocity-based formulation is proposed that simulates large deformation of a weakly compressible hyper-elastic solid on an Arbitrary Lagrangian-Eulerian (ALE) framework. The proposed solver, which is implemented in OpenFOAM software, allows for flexible grid movement, i.e. mesh points are not forced to follow material points, as well as for the employment of various material models such as Mooney–Rivlin and Neo-Hookean constitutive laws. Three challenging 2-D and 3-D test cases including torsion, bending and pressing of solid objects are presented to examine and discuss the accuracy and flexibility of the proposed solver. Furthermore, more light is shed on the concept of the pressure in compressible solids and appropriate boundary conditions at traction boundaries. [ABSTRACT FROM AUTHOR]

This paper presents the basic methodologies used for Natural Smoke and Heat Ventilation Systems design under wind conditions, along with chosen numerical tools such as Computational Fluid Dynamics method and evacuation modelling as their supplement. First, results of comparison of different natural ventilation systems a series of transient CFD simulations are shown, illustrating potential problems in the system design with traditional approach. Later in the paper, authors focus on complete analysis of fire related phenomena in wind conditions, for a real historical shopping mall in Warsaw with vertical natural smoke ventilators. All of the steps of the analysis are described, together with some practical remarks. The reference analysis were carried in ANSYS Fluent CFD model, followed by evacuation study with building Exodus software. [ABSTRACT FROM AUTHOR]

This paper investigates the leakage characteristics of brush seals including the flow field characteristic of brush seal and the effects of structural parameters on the leakage characteristic of brush seals with the consideration of bristle deflection. The flow field characteristic of brush seal was discussed based on three-dimensional (3-D) computational model of brush seal, two-way fluid–structure interaction and moving grid technique. Then the effect of structural parameters on the leakage characteristic of brush seals was investigated from theoretical and numerical simulation perspectives with the emphasis on an improved prediction formula of leakage flow rate of brush seals. As illustrated in the analysis of the leakage characteristics of brush seals, (1) the leakage with the influence of bristle deflection is closer to the results of experiment relative to that without bristle deflection, and increases with the increasing inlet/outlet pressure ratios, which validate the developed 3-D computational model with bristle deflection to be more reasonable; (2) the flow field characteristics (pressure and velocity) of brush seal are revealed reasonably; (3) with the increasing of the height of backing plate fence, the clearance of brush wire and the axial clearance between brush bristle and back plate, the leakage factor rises and then reaches a stable value when the clearance of brush is larger than 0.3 mm; moreover, (4) with the increase of brush wire diameter, the leakage factor decreases firstly and then tends to stabilization, while rapidly decreases at first, then slowly decreases, and lastly tends to a value when the bristle row number increases; (5) the reliability and accuracy of the proposed prediction equation for brush seals is validated to be high by the CFD computational results. The efforts of this paper provide a useful theoretical and numerical method to clearly understand the leakage characteristics of brush seal, which is beneficial to improve the design of brush seals. [ABSTRACT FROM AUTHOR]

Accurate prediction of hydrodynamic forces on offshore structures is critical for safe and cost effective design of fixed and floating offshore structures exposed to a harsh environment. In the present paper, nonlinear interactions between regular waves and a single surface-piercing truncated circular column have been investigated using a frequency domain potential flow solver (DIFFRACT) and a full CFD solver in OpenFOAM for direct comparisons. Both the predicted free surface elevation around the column and the total force acting on the column have been analysed and compared with experimental data from MOERI. The degree of non-linearity and the contribution of each harmonic to the free surface run-up and wave forces have been examined, and evaluations of the accuracy and computational efficiency of the potential flow solver and the full CFD solver are provided and compared in the paper. Also of note are the local forms of the scattered waves around the column in numerical simulations, which are consistent with the Type-1 and Type-2 patterns identified in physical experiments at Imperial College. [ABSTRACT FROM AUTHOR]

The paper presents a numerical study on an 18 cm-diameter liquid pool fire in a reduced-scale and mechanically-ventilated enclosure. The enclosure walls are made of a calcium silicate layer and a steel layer on five sides, the remaining sidewall is made of heat-tempered glass. The ventilation system is extracted mechanically with free air inlet. Three air renewal rates (ARR) and open atmosphere conditions are considered in the numerical study. Computational Fluid Dynamics (CFD) simulations are carried out with Fire Dynamics Simulator (FDS 6.7.5). The default evaporation model in FDS (i.e., forced convection approach) is compared to a natural convection approach implemented in the source code. The results show that the oscillatory combustion, occurring at ARR = 15 h−1, is best captured by the natural convection approach. It is also found that prescribing the fuel Auto-Ignition Temperature (AIT) is important to capture the fire oscillations and (local) flame quenching. At ARR = 8 h−1, extinction occurs. It is found that prescribing the fuel AIT allows to prevent spurious oscillatory combustion. At ARR = 22.5 h−1, there is a stable steady-state burning regime for which (as well as for open atmosphere conditions) prescribing the fuel AIT is not crucial. • Fire burning regimes are well predicted in a wide range of ventilation conditions. • Oscillatory combustion is captured by natural convection for evaporation modeling. • Prescribing Auto-Ignition Temperature is important in capturing fire oscillations. • Prescribing AIT prevents spurious fuel re-ignition in under-ventilated conditions. [ABSTRACT FROM AUTHOR]

During a severe accident in light water reactor (LWR), hydrogen concentration can overpass the flammability limits locally, so the correct simulation of its behavior during a release is critical. The capability assessment of computational fluid dynamics tools to calculate the hydrogen distribution under different conditions has been the focus of intense research worldwide. In this context, the OECD/NEA conducted an international benchmark exercise (IBE-3), which was focused on the break-up of a stratified layer of a light gas by a vertical jet. The participants performed their simulations before the experiment data was released. When the data was released, it was noticed that a combination of several parameters like the mesh, turbulence model or solver controls were responsible for the broad differences between the participants’ results. To obtain information about how each parameter affects the simulation, a post-test sensitivity analysis has been done by the UPM. In this paper, the IBE-3 experiment simulation with GOTHIC 8.0 is presented along with extensive sensitivity analyses of the relevant parameters. The first objective of the work is to test the capability of GOTHIC 8.0 to simulate properly a gas stratification break-up by a vertical jet with a relatively coarse mesh. The second objective of the paper is to relate each sensitivity parameter with each other and with the experiment through the Parameter Influence Chart, a helpful tool specially designed for this purpose. [ABSTRACT FROM AUTHOR]

This study aims at demonstrating the capability of the immersed-body method to simulate wave–structure interactions using a non-linear finite-element model. In this approach, the Navier–Stokes equations are solved on an extended mesh covering the whole computational domain (i.e. fluids and structure). The structure is identified on the extended mesh through a nonzero solid-concentration field, which is obtained by conservatively mapping the mesh discretising the structure onto the extended mesh. A penalty term relaxes the fluid and structural velocities to one another in the regions covered by the structure. The paper is novel in that it combines the immersed-body method with wave modelling and mesh adaptivity. The focus of the paper is therefore on demonstrating the capability of this new methodology in reproducing well-established test cases, rather than investigating new physical phenomena in wave–structure interactions. Two cases are considered for a bottom-mounted pile. First, the pile is placed in a numerical wave tank, where propagating waves are modelled through a free-surface boundary condition. For regular and irregular waves, it is shown that the wave dynamics are accurately modelled by the computational fluid dynamics model and only small discrepancies are observed in the close vicinity of the structure. Second, the structure is subjected to a dam-break wave impact obtained by removing a barrier between air and water. In that case, an additional advection equation is solved for a fluid-concentration field that tracks the evolution of the air–water interface. It is shown that the load associated with the wave impact on the structure compares well with existing numerical and experimental data. [ABSTRACT FROM AUTHOR]

Wind behavior in urban areas is receiving increasing interest from city planners and architects. Computational fluid dynamics (CFD) simulations are often employed to assess wind behavior around buildings. However, the accuracy of CFD simulations is often unknown. Measurements can be used to help understand wind behavior around buildings more accurately. In this paper, a model-based data interpretation framework is presented to integrate information obtained from measurements with simulation results. Multiple model instances are generated from a model class through assigning values to parameters that are not known precisely, including those for inlet wind conditions. The information provided by measurements is used to falsify model instances whose predictions do not match measurements and to estimate the parameter values of the simulation. The information content of measurement data depends on levels of measurement and modeling uncertainties at sensor locations. Modeling uncertainties are those associated with the model class such as effects associated with turbulent fluctuations or thermal processes. The model-based data interpretation framework is applied to the study of the wind behavior around the buildings of the Treelodge@Punggol estate, located in Singapore. The framework incorporates modeling and measurement uncertainties and provides probability-based predictions at unmeasured locations. This paper illustrates the possibility to improve approximations of modeling uncertainties through avoiding falsification of the entire set of model instances. It is concluded that the framework has the potential to infer time-dependent sets of parameter values and to predict time-dependent responses at unmeasured locations. [ABSTRACT FROM AUTHOR]

This paper investigates pollutant removal at pedestrian level in urban canopy layer (UCL) models of medium packing density ( λ p = λ f = 0.25) using computational fluid dynamics (CFD) simulations. Urban size, building height variations, wind direction and uniform wall heating are investigated. The standard and RNG k − ε turbulence models, validated against wind tunnel data, are used. The contribution of mean flows and turbulent diffusion in removing pollutants at pedestrian level is quantified by three indicators: the net escape velocity ( NEV ), the pollutant transport rate ( PTR ) across UCL boundaries and their contribution ratios ( CR ). Results show that under parallel approaching wind, after a wind-adjustment region, a fully-developed region develops. Longer urban models attain smaller NEV due to pollutant accumulation. Specifically, for street-scale models (∼100 m), most pollutants are removed out across leeward street openings and the dilution by horizontal mean flows contributes mostly to NEV . For neighbourhood-scale models (∼1 km), both horizontal mean flows and turbulent diffusion contribute more to NEV than vertical mean flows which instead produce significant pollutant re-entry across street roofs. In contrast to uniform height, building height variations increase the contribution of vertical mean flows, but only slightly influence NEV . Finally, flow conditions with parallel wind and uniform wall heating attain larger NEV than oblique wind and isothermal condition. The paper proves that by analysing the values of the three indicators it is possible to form maps of urban breathability according to prevailing wind conditions and known urban morphology that can be of easy use for planning purposes. [ABSTRACT FROM AUTHOR]

• The standard k-ε model is better than SST k- ω model, BSL-RSM model, RNG k-ε model and realizable k-ε model in predicting the loss coefficient of the valve during the transient process. • The change of the valve loss coefficient and valve flow coefficient with the valve opening is roughly divided into three areas. • Numerical simulation methodology established in this paper may provide a guideline to develop the butterfly check valve model when a small modular reactor is under natural circulation conditions. The butterfly check valve is widely used in small modular reactors to prevent pumps from being damaged by backflow during normal operating conditions. However, the large flow resistance of the valve has an important impact on the flow characteristics of the reactor coolant system during natural circulation state. The present study aims to perform and validate a series of simulations of the flow characteristics for a butterfly check valve in a small modular reactor employing the computational fluid dynamics (CFD) method. Steady state simulations were first performed to obtain the relationship between the valve loss coefficient and the valve opening angle. Based on dynamic mesh techniques, transient state simulations with five different turbulence models, standard k-ε model, RNG k-ε model, realizable k-ε model, SST k- ω model, and BSL-RSM model, were applied to obtain valve loss coefficient and valve flow coefficient respectively. Furthermore, experiments were carried out and compared with the results of transient numerical simulations. It must be pointed out that compared to other turbulent models, the simulation results using the standard k-ε model agree better with the experiment results. The experimental and numerical results show that the numerical simulation methodology established in this paper can be used to obtain the valve flow coefficient when a small modular reactor is under natural circulation conditions, and the coefficient can be used to accurately analyze the natural circulation characteristics of small modular reactors. [ABSTRACT FROM AUTHOR]

This paper reports upon developments in the simulation of the passive control of combustion dynamics in industrial gas turbines using acoustic attenuation devices such as Helmholtz resonators and perforated liners. Combustion instability in gas turbine combustors may, if uncontrolled, lead to large-amplitude pressure fluctuations, with consequent serious mechanical problems in the gas turbine combustor system. Perforated combustor walls and Helmholtz resonators are two commonly used passive instability control devices. However, experimental design of the noise attenuation device is time-consuming and calls for expensive trial and error practice. Despite significant advances over recent decades, the ability of Computational Fluid Dynamics to predict the attenuation of pressure fluctuations by these instability control devices is still not well validated. In this paper, the attenuation of pressure fluctuations by a group of multi-perforated panel absorbers and Helmholtz resonators are investigated both by experiment and computational simulation. It is demonstrated that CFD can predict the noise attenuation from Helmholtz resonators with good accuracy. A porous material model is modified to represent a multi-perforated panel and this perforated wall representation approach is demonstrated to be able to accurately predict the pressure fluctuation attenuation effect of perforated panels. This work demonstrates the applicability of CFD in gas turbine combustion instability control device design. [ABSTRACT FROM AUTHOR]

The work here presented has been performed in the framework of a research project aimed to investigate two-phase (boiling) flows in pressurized water reactors (PWR). CFD investigations of a rod bundle have been conducted while a new experimental facility (ROFEX) was constructed in Helmholtz Zentrum Dresden-Rossendorf (HZDR) for the generation of quality validation data. The apparatus consists of a 3 × 3 rod bundle inside a Plexiglas vertical pipe. The results summarized in this paper are considered as a pre-investigation, being the final goal to be able to predict accurately boiling water flows under high pressure around rods. For this purpose, three steps were defined: analysis of single-phase flows in such geometry, analysis of the multiphase flow when using a refrigerant as a working fluid and, finally, the analysis of a multiphase flow using water. The single-phase approach allows gaining experience regarding the turbulence behaviour of the flow, while the multiphase investigation of the refrigerant simplifies the experimental conditions since it is possible to get boiling situations at lower pressure level. At the moment of writing this paper, the authors were focused on the first step (single-phase flows at low pressure), since this not only made possible to better understand the turbulence in that geometry, but it also resulted in valuable feedback to the experimentalists on improving the construction of the facility. In parallel, HZDR researchers have been developing a new tomography measurement technique to measure gas content in multiphase flows. [ABSTRACT FROM AUTHOR]

Plate fin-and-tube heat exchangers operate in a cross-flow arrangement. The numerical studies of performance of these heat exchangers encounter difficulties in the proper prediction of the total gas side temperature difference, because thermal contact resistance between the fin and the tube is unknown. The local measurements of its value are difficult to carry out. This paper presents a modified method for estimating the mean value of thermal contact resistance in a plate fin-and-tube heat exchanger. The proposed computational method is based on the CFD simulations and experimental measurements and it allows an accurate prediction of the total gas-side temperature difference in a heat exchanger. Furthermore, this paper presents the modified method of determining the average heat transfer coefficient for the air flow, which is similar to the technique used for experimental data reduction. [ABSTRACT FROM AUTHOR]

The behavior of binary droplet collision, exposed to an external electric field is studied numerically. Based on a fundamental understanding of the role of the electric field in the coalescence of aqueous drops in an immiscible oil phase, it is possible to optimize the design and operation of these external stimulators. In this research, numerical modeling of electrocoalescence is implemented, using Computational Fluid Dynamics (CFD) methods. Level set method is used to evaluate water droplet evolution in an oil phase under a novel concentric semi-elliptic non-uniform electric field configuration. The observations show that the shape of applied non-uniform fields can remarkably alter the electrocoalescence performance in a nontrivial way, which is sensitive to the drop-medium system. In addition to the shape of the medium, some other parameters such as droplets initial distance, initial skew angle of the droplets, applied voltage amplitude and oil viscosity are analyzed in the present paper. Our results can be useful in designing an optimum electrode configuration, achieving an efficient electrocoalescence. [ABSTRACT FROM AUTHOR]

• Experimental research on ceramic panel carried out for the first time. • Determination of the pressure drop of the fluid flowing through the collector. • Determination of the thermal performance of ceramic solar panel. • Development and positive validation of the ceramic CFD model. The paper presents the results of the laboratory testing and numerical simulations of ceramic solar panels. The experimental research was carried out in artificial (laboratory) operating conditions. Rise in temperature and pressure drop of the fluid flowing through the collector was measured. As a result of the tests, the linear relationship between efficiency and reduced temperature difference was determined. While the pressure drop was approximated by the exponential function. Another research method based on numerical modelling using Computational Fluid Dynamics (CFD) algorithms was applied in this study. The three-dimensional geometric model of the ceramic panel was developed using the application included in the Ansys v. 19.2 package. The data obtained from computer simulations were compared with the results of the experiment to validate the numerical model. In order to find potential opportunities to increase the efficiency and due to the fact that the ceramic panel can be made in various inlet and outlet configurations, three simulation cases were considered: diagonal, top – bottom, and left – right. As the results of numerical calculations showed, the largest flow irregularity occurred in the last configuration. Based on the analysis of the test results, it can be concluded that, in spite of some disadvantages, ceramic panels can compete with traditional solar collectors currently available on the market. [ABSTRACT FROM AUTHOR]

Defining a suitable erosive factor for interrill erosion has been a long-going discussion that was not resolved by experimental results. In this paper, by using computational fluid simulations of individual raindrop impacts, the relevance of four erosive factors was assessed for a range of soil resistance, rainfall type and water layer depth. Computation results show that the erosivity exponent associated to the erosive factors had a very low sensitivity to soil resistance. This confirms the common practice of separating rainfall erosivity from soil erodibility. The erosivity exponent was found to be very sensitive to the rainfall type. Therefore, an universal exponent could not be found, its value depending on the rainfall type. As a result of the balance between the shear stress development and the protective effect of the water layer, the soil detachment rate was maximum for a specific water depth. This supports to better account for the water layer depth in erosion models. Overall, the computational approach shows that the choice of an erosive factor may not be of practical importance. It also encourages for new experimental designs, able to evaluate soil detachment by raindrops — and not only the amount of splashed soil. • The choice of a specific erosive factor is not of importance for practical purpose. • Soil erodibility and rainfall erosivity can continue to be considered as independent. • The type of rain is quite important when using an erosive factor. [ABSTRACT FROM AUTHOR]

The study of molten pool characteristics is a powerful means of determining the quality of laser additive manufacturing forming. In this paper, a three-dimensional transient thermal flow field numerical model of Ti6Al4V powder processed by LPBF is developed based on FLOW-3D software, and the dynamic evolution of the molten pool with fixed process parameters is quantitatively described using dimensionless numbers in computational fluid dynamics. It is shown that the main heat transfer mode of the molten pool is thermal convection; the evaporative back sitting pressure, surface tension and Marangoni shear force are the main driving forces for the evolution of the molten pool. Furthermore, the influence of key process parameters on the heat flow field of the molten pool was analyzed. When the laser power was 300 W, the depression depth and molten pool depth caused by the recoil pressure were significantly larger, and the isothermal density of the solidification region was more intensive; when the scanning speed was increased from 0.4 m/s to 0.8 m/s, the molten pool length was reduced from 524 μm to 410 μm, and the line energy density was reduced making the amount of melted powder decrease. The wettability and fluidity of the molten state metal becomes worse; when the scanning interval increases to 120 μm, a large number of incompletely melted powder tracks cannot lap correctly at the midline of the double track. The results of the above simulations achieve a high degree of agreement with the surface quality of the specimens during the experiments, which provides guidance for quantitative analysis of molten pool evolution and prediction of Ti6Al4V forming quality. • Based on the Discrete Element Method, a Ti6Al4V powder-scale LPBF thermal flow field model was established. • The influence of key process parameters on surface forming quality was studied. • The experiment and simulation agree well, providing guidance for optimizing the forming of Ti6Al4V. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the effect of flow non-ideality on the Mach disk pattern occurring in axisymmetric under-expanded supersonic jets. The explored conditions are found in the non-ideal gas region close to the liquid–vapor saturation curve and the critical point, where involved thermodynamics cannot be accurately described by the ideal gas law. Numerical simulations of steady inviscid compressible flows are carried out by adopting the polytropic ideal gas model and improved Peng–Robinson thermodynamic model, via the open-source computational fluid dynamics code SU2. To properly resolve the Mach disk position and radius, a mesh adaptation procedure is used. An assessment of the most suitable mesh adaptation criteria for the considered ideal and non-ideal flow configurations is carried out, considering isotropic and anisotropic mesh adaptation criteria. The best mesh adaptation criterion for ideal and non-ideal under-expanded jets results to be the anisotropic criterion based on the Hessian of the density and Mach number field. Then, the effects of the flow non-ideality on the Mach disk are investigated by simulating different operating conditions of under-expanded nozzle jets of five different vapors. For nitrogen, oxygen, carbon dioxide, the Mach disk moves downstream and has a smaller radius with a higher level of non-ideality. Conversely, for siloxanes MM and MDM, the Mach disk moves upstream and has a larger radius as the non-ideality of the flows increases. • Numerical simulations of under-expanded jets in ideal and non-ideal regimes. • Assessment of mesh adaptation criteria for ideal and non-ideal under-expanded jets. • Anisotropic mesh adaptation based on density and Mach number are the best criteria. • Simulation of under-expanded jets with five fluids in non-ideal regimes. • Investigation of the non-ideal effects on the position and radius of Mach disk. [ABSTRACT FROM AUTHOR]

Successful delivery of drugs to the Olfactory region (OR) is the key to treating diseases through the nasal cavity. The purpose of this paper is to investigate the effect of auxiliary airflow on particle deposition in the OR during nasal drug administration. A realistic 3D nasal ensemble model was reconstructed from CT scans of the head of a healthy adult. Computational fluid dynamics (CFD) was used to simulate the effect of auxiliary airflow on the deposition of drug particles in the OR during nasal administration. The discrete phase model (DPM) was adopted to track the deposition trajectories of drug particles. Three auxiliary airflows were selected together with three spray cone angles, four particle sizes, five drug particle delivery velocities and three specific injection positions on the deposition fraction of drug particles in the OR were analyzed. The results indicated that the effect of auxiliary airflow on the deposition fraction of drug particles of different particle sizes in the OR is significant. The delivery efficiency of injection position C is always the greatest. A delivery velocity of 15 m/s is more favorable for nasal administration and the effect of spray cone angle is proportional to the auxiliary airflow. Computational results should be helpful for experimental studies and future nasal optimization. [Display omitted] • The effect of auxiliary airflow on particle deposition is systematically studied. • Drug particles are released at specific locations in the nasal cavity. • The effects of particle parameters are systematically investigated. • Some mechanisms of the effect of auxiliary airflow on deposition are studied. [ABSTRACT FROM AUTHOR]

The scale effect on aerodynamics determines, to some extent, the development trend and limitation of large vertical axis wind turbines (VAWTs). Among many factors, Reynolds number is an important one affected by such effects and is therefore often used as a criterion to distinguish between small-scale and large-scale wind turbines. In this paper, a dimensionless analysis was first conducted, and the results showed that scaling the wind turbine as a whole only led to a change in Reynolds number, while other key factors remained constant. Based on such understanding, a univariate analysis was then carried out to investigate the effect of Reynolds number variation due to scaling effects on the aerodynamic performance of VAWTs. In the study, a series of high-resolution numerical simulations were performed on a simplified single-bladed VAWT model. By directly scaling the model size, the operating Reynolds number of the wind turbine was made to vary in the range of 1 × 1 0 4 to 5 × 1 0 6 at a specific solidity and reduced frequency. The analysis shows that over the range of Reynolds number investigated, as the size of the wind turbine model increases, the flow separation nearby the blade decreases, the strength of the dynamic stall vortex becomes weaker, and the power coefficient of wind energy extraction generally tends to increase, thus indicating that large-scale wind turbine is generally beneficial aerodynamically. Specifically, when VAWTs operate in a Reynolds number ranging from 5 × 1 0 4 to 5 × 1 0 5 , the power coefficient increases significantly as the size of wind turbine increases, while when operating in the range of 5 × 1 0 5 ∼ 5 × 1 0 6 , the power coefficient still tends to increase, but in a decreasing increment ratio. • This paper verified the feasibility of large-scale wind turbines. • The power coefficient of vertical axis wind turbine increases as its scale enlarges. • The power coefficient of vertical axis wind turbine is sensitive to Reynolds number variation when the scale is small. • The vertical axis wind turbines are not suitable for very low Reynolds number conditions. [ABSTRACT FROM AUTHOR]

• The air-flow due to droplet entrainment in inkjet print-zones is simulated for a range of conditions. • Increasing the pen-to-paper spacing causes the vortex upstream of the print-zone to become deformed. • Adding through flow from the inlet to outlet is an effective remedy for the print defect. Air-flow oscillations in inkjet print-zones give rise to undesirable print defects due to misplacement of low Stokes number satellite droplets. The problem is studied numerically using a novel dispersed-phase continuum method, that, due to the separation of length scales, permits the force exerted by the multitude of high Stokes number main droplets to be modelled as a continuous smooth field. The oscillations seem to be linked to the deformation of the primary vortex upstream of the print-zone. It is also shown that introducing extra flow in the direction of the paper motion is an effective remedy for the oscillations. [ABSTRACT FROM AUTHOR]

Abstract: The objective of the present paper is to study the oil flows from damaged submarine pipelines with different leak sizes. CFD (computational fluid dynamic) simulations with FLUENT software are carried out to investigate the process of oil spill from submarine pipeline to free surface. Effects of oil density, oil leaking rate, leak size and water velocity on the oil spill process are examined. High density, slow leaking, small leak size or fast current brings about long time for oil reaching the maximum horizontal migrate distance when it reaches surface. And this maximum horizontal migrate distance increases with the increase of leak size or water velocity, while increases with the decrease of leaking rate. Then, the dimensionless time required for oil droplets which have the longest horizontal migrate distance when they reach the sea surface and the dimensionless longest horizontal distance the droplets migrate when they reach the sea surface are analyzed and the fitting formulas are obtained. Only the formula for the dimensionless longest horizontal distance versus dimensionless density meets the polynomial, other five formulas meet the natural logarithm distribution. Using the formulas we can obtain when and where to see oil reaching the sea surface, and conduct rapid response. Finally, the maximum horizontal migration distance of oil at certain time is predicted, and a forecasting model is proposed. The using methods of fitting formulas and the forecasting model are shown in the paper by examples. These calculated results provide useful guidance to place the oil containment boom. [Copyright &y& Elsevier]

Abstract: When performing unsteady time-dependent Computational Fluid Dynamics (CFD) calculation to investigate dynamic wind–structure interactions, turbulence whose mean and fluctuating velocity components satisfy the requirements of the Atmospheric Boundary Layer (ABL) of the specified terrain category must be imposed at the inlet of the computational domain at each time step. This paper proposes incorporation of the local Differential Quadrature Method (DQM) and the recycling technique to simulate inflow turbulence for wind engineering applications. Local DQM is utilized to help simulate the high-frequency component of turbulence because of its inherent high accuracy. The recycling technique is utilized to control the mean-velocity profile and boundary layer height. In this paper, local DQM is first described and verified by a numerical simulation of turbulence in a channel. It is then utilized in conjunction with the recycling technique to generate three kinds of turbulent boundary layers with different mean-velocity profiles. The results show that local DQM is a good approach to generation of inflow turbulence, particularly to increase the turbulence energy of high-frequency components. [Copyright &y& Elsevier]

Abstract: The aim of this paper is the evaluation and validation of the Eulerian–Lagrangian Spray Atomization (ELSA) model implemented in a CFD code by Renault. ELSA is an integrated model for capturing the whole spray evolution, in particular including primary break-up and secondary atomization. Two-dimensional simulations have been performed during the study, which is in fact enough to capture some of the main features of the spray, such as the spray penetration and the axial velocity. A mesh independence study has also been carried out in order to characterize the lowest mesh size that can be used to correctly characterize the spray. Furthermore, the two-equation turbulence model has been adjusted by changing some of the parameters of the dissipation rate transport equation in order to accurately characterize the spray. Finally some analyses of the results obtained, in terms of penetration, liquid mass fraction and droplet number and size, are presented in the last section of the paper. [Copyright &y& Elsevier]

Abstract: This study is a sequel to the paper of Savage and Oger ( this issue) that reviewed experimental studies of airslides. These devices make use of fluidization to facilitate the transport of granular materials over long distances. The present paper describes a detailed and comprehensive consideration of the various contributions to the governing multiphase flow equations and proceeds to carry out numerical simulations of airslide flows and compare the results with laboratory experiments. It was carried out in part using the open source multiphase flow CFD program MFIX. Revisions and additions to the governing equations used in the distribution version of MFIX were made. The results of previously published molecular dynamics simulations were used to formulate a revised radial distribution function. The forms of the quasi-static stress contributions were designed to permit the development of higher concentration flows typical of experimentally observed airslide flows. Finally, additional terms were included in the particle fluctuation energy equation to account for (i) the viscous dissipation of the fluctuating particles due to the interstitial air, and (ii) the energy source term arising from the transfer of energy from the fluid to the particles. These expressions have been incorporated in the computational scheme and simulations of fluidized granular flows in a rectangular channel having frictional side walls were carried out. Some initial exploratory calculations were performed to examine the effects of various parameters on the mass flow rates and the velocity profiles. Different wall conditions were studied by varying the particle and wall restitution coefficients. The effects of varying the minimum fluidization velocity and the solid fraction thresholds were also examined. The simulation scheme was then applied to model two of the better documented fluidized chute flow experiments; those of Botterill and Bessant (1976), and the McGill University fluidized solids flow channel experiments of Liot (1979) and Chan (1979). Results of these computations and comparisons with observed experimental airslide behavior are discussed. Good agreement is found between the simulations and the experimental airslide flow characteristics. [Copyright &y& Elsevier]

Abstract: This paper introduces a new CFD based Immersed Body Force (IBF) model, and examines the performance of a new type of tidal turbine, the Momentum Reversal Lift (MRL) turbine, developed by Aquascientific Ltd using the open source computational fluid dynamics (CFD) code OpenFOAM. The IBF model was added as a forcing function into the existing large eddy simulation model to create a momentum change in the fluid flow induced by the MRL turbine. An experimental study was performed on a small scale model to determine the operating efficiency of the turbine and the data was used to validate the IBF model. The power output curves from both the IBF model and the experiments showed good agreement in most of the data except for a few discrepancies at higher torques, due to venturi flow created by the proximity of the computational domain''s wall boundary to the turbine. Thus the results presented in this paper show the fidelity of the IBF model and can be used for different tidal turbine numerical modelling. [Copyright &y& Elsevier]

Abstract: Prediction of turbine-to-turbine interaction represents a significant challenge in determining the optimized power output from a tidal stream farm, and this is an active research area. This paper presents a detailed work which examines the influence of surrounding turbines on the performance of a base case (isolated turbine). The study was conducted using a new CFD based, Immersed Body Force (IBF) model, which was validated in the first paper, and an open source CFD software package OpenFOAM was used for the simulations. The influence of the surrounding turbines was investigated using randomly chosen initial lateral and longitudinal spacing among the turbines. The initial spacing was then varied to obtain four configurations to examine the relative effect that positioning can have on the performance of the base turbine. [Copyright &y& Elsevier]

Abstract: Among many research studies on fluidized bed membrane reactors, only very few focus on the details of the effects of gas permeation through the membranes on the hydrodynamic properties of the membrane-assisted fluidized bed. For this reason, in the first part of this paper, a novel hybrid Immersed Boundary Method (IBM) Discrete Particle Model (DPM) has been developed. In the second part of the paper, this model is employed to investigate fluidized bed membrane reactors in more detail. Simulations without membrane inserts (having vertical membranes at the side walls instead), with membrane tubes in an in-line arrangement and membranes in a staggered arrangement are compared with each other. The time-averaged particle fraction maps display a lower bed height for the simulations with inserts. A very important aspect of the simulation with gas extraction/addition via the side walls is the solids circulation; an inversion of the solids circulation is observed when gas is added via the side walls with altered bubble properties. Because of this phenomenon, the bubble size counter-intuitively decreases when gas is added, and increases slightly when gas is extracted. The latter is a result of the existence of compacted zones near the membranes. For the simulation cases with membrane inserts, the solids circulation and bubble properties are different; in these cases they mainly depend on the local fluidization velocity, and not so much on the extent of permeation itself. Although the arrangement of the membrane tubes plays only a minor role in this matter, their presence has a pronounced influence on the bubble size. The system''s energy and energy dissipation are both smaller for the simulations with inserts compared to those with permeation via the side walls. Also in this respect, the local fluidization velocity is found to be more important than the extent of permeation. [Copyright &y& Elsevier]

Abstract: In numerical simulations of fuel rod bundle flow fields, the unsteady Navier–Stokes equations have to be solved in order to determine the time (phase) dependent characteristics of the flow. In order to validate the simulations results, detailed comparison with experimental data must be done. Experiments investigating complex flows in rod bundles with spacer grids that have mixing devices (such as flow mixing vanes) have mostly been performed using single-point measurements. In order to obtain more details and insight on the discrepancies between experimental and numerical data as well as to obtain a global understanding of the causes of these discrepancies, comparisons of the distributions of complete phase-averaged velocity and turbulence fields for various locations near spacer-grids should be performed. The experimental technique Particle Image Velocimetry (PIV) is capable of providing such benchmark data. This paper describes an experimental database obtained using two-dimensional Time Resolved Particle Image Velocimetry (TR-PIV) measurements within a 5×5 PWR rod bundle with spacer-grids that have flow mixing vanes. One of the unique characteristic of this set-up is the use of the Matched Index of Refraction technique employed in this investigation to allow complete optical access to the rod bundle. This unique feature allows flow visualization and measurement within the bundle without rod obstruction. This approach also allows the use of high temporal and spatial non-intrusive dynamic measurement techniques namely TR-PIV to investigate the flow evolution below and immediately above the spacer. The experimental data presented in this paper includes explanation of the various cases tested such as test rig dimensions, measurement zones, the test equipment and the boundary conditions in order to provide appropriate data for comparison with Computational Fluid Dynamics (CFD) simulations. Turbulence parameters of the obtained data are presented in order to gain insight of the physical phenomena. [Copyright &y& Elsevier]