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In this paper, an analytical approach combined with a two-dimensional computational fluid dynamics (CFD) model is pursued to simulate the fluid flow in a monopropellant thruster for satellite propulsion systems. The thruster utilizes hydrogen peroxide (H2O2) as a green propellant at a concentration of 87.5%, with a catalytic bed based on spherical silver particles. Through a parametric analysis of particle diameter, we aim to optimize the design of a monopropellant thruster capable of generating a thrust of 20N. For this purpose, a program in CFD code in the commercially available ANSYS Fluent software is used to solve the energy, momentum, mass transfer, and species transport equations governing the thruster system. The local thermal non-equilibrium (LTNE) approach is used to describe the heat transfer occurring through both the solid and fluid phases within the catalyst bed. The results demonstrate that particle size significantly affects the thermal behaviour, species mass fraction, and exit velocity. An optimum diameter of 0.65mm exhibits the optimal performance of the monopropellant thruster, ensuring efficient decomposition of H2O2 at 968K and providing the required level of thrust force with a specific impulse of about 120s. [ABSTRACT FROM AUTHOR]

Flow past bluff bodies like square cylinders is important in engineering applications, but flow patterns behind staggered cylinder arrangements remain poorly understood. Existing studies have focused on tandem or side-by-side configurations, while offset orientations have received less attention. The aim of this paper is to numerically investigate flow dynamics and force characteristics behind two offset square cylinders using the single relaxation time lattice Boltzmann method. The effects of changing both the Reynolds number (Re = 1-150) and gap spacing ratio (g* = 0.5-5) between the cylinders are analyzed. Instantaneous vorticity contours, time histories of drag and lift coefficients, power spectra of lift, and force statistics are used to characterize the flow. Different flow regimes have been identified in various ranges of Re and g* - including steady, chaotic, flip-flopping, single-bluff body, and fully developed flows. Larger spacings led to more regular vortex dynamics and force statistics. Smaller spacings promoted complex interactions and modulated forces. Offset cylinder orientation and spacing significantly influence flow features in staggered arrangements. The findings provide new modalities for controlling fluid dynamics past bluff bodies by tuning Re and gap parameters. [ABSTRACT FROM AUTHOR]

The liquefied natural gas (LNG) fuel tank in a large container ship is loaded with liquid LNG at an ultra-low temperature (-163°C), there is a significant temperature difference in the cargo hold area where the entire fuel tank is located, which will have an important impact on the steel grade design and structural safety of the cargo tank in container ship. This paper develops two heat transfer models using Computational Fluid Dynamics method (CFD method) and an analytical method to analyze the temperature distribution in a large container ship equipped with Type-B LNG fuel tank. These models incorporate the arrangement and heat transfer characteristics of LNG fuel tanks. The temperature field analysis is conducted under typical the environmental conditions specified in the Code for the Construction and Equipment of Ships Transporting Liquefied Gas in Bulk (IGC Code) and the United States Coast Guard Code (USCG Code), based on the CFD method and the analytical method, and the results of temperature field distribution are compared. Additionally, a parametric analysis of the hull temperature field is further carried out, the results show that the thermal conductivity of the insulation layer in LNG storage tanks and the types of the loaded liquid cargo have a limited impact on the final temperature field distribution in hull structure. However, the selection of steel grade in the local structure of the cargo hold, especially in the inner hull part, may lead to significant changes. [ABSTRACT FROM AUTHOR]

This paper investigates the behavior of magnetohydrodynamic (MHD) peristaltic flow with electroosmosis. The Jeffrey fluid in microchannel under the influence of homogeneous-heterogeneous chemical reaction has been taken. The heat absorption and nonlinear radiation are also scrutinized here. This study contributes to the fundamental understanding of complex fluid dynamics in microscale systems and offer valuable insights for designing and optimizing microfluidic devices. In the framework of mathematical simulation, the relevant dimensional nonlinear equations are reduced into dimensionless equations by using linear transformations. Thus Debye-Hückel linearization has been employed. The streamline approach with mathematical modelling has been performed within the limits of δ ≪ 1 and Re → 0. The appropriate equations for temperature and concentration with boundary conditions are solved by using perturbation approach whereas, the exact solution is found for velocity equation. A graphical depiction of crucial physical characteristics on velocity, temperature, concentration and streamlines are reported in the last section. It is observed that the velocity distribution decreases for the higher value of M (0.5 ≤ M ≤ 2) however, it increases for the escalating values of U hs (− 0.5 ≤ U hs ≤ 1.5). When R n (0.1 ≤ R n ≤ 0.6) gets stronger then temperature profile decreases. It is noticed that the concentration profile decays owing to enhancement in Sc (− 0.5 ≤ Sc ≤ 1.5). As the M (0.5 ≤ M ≤ 2) increases, the size of trapped bolus decreases. Escalating values of temperature ratio parameter θ w (1.0 ≤ θ w ≤ 1.6) enhances the Nusselt number. The novelty of this study lies in the comprehensive analysis of multiple complex phenomena in a single framework. The interplay between MHD electroosmotic flow, homogeneous heterogeneous chemical reactions, peristalsis, nonlinear thermal radiation, heat absorption and no-slip condition has not been explored in previous research. [ABSTRACT FROM AUTHOR]

Regarding the airfoil optimization design of multi-rotor unmanned aerial vehicles, this paper proposes an integral airfoil design method based on upper airfoil contour optimization. Firstly, by designing concave descent input curves with 0-1 distribution, the upper arc of different optimized airfoils is obtained using the Tangent circles method. Secondly, an integral airfoil generation method is developed after establishing the middle arc. As the upper and lower arcs of different shapes are randomly combined, various airfoil profiles are obtained by random assortment. Finally, the effectiveness and accuracy of the designed airfoil are validated through Python programming. The airfoil is generated by the XFOIL program, and the optimal airfoil is output with a lift-todrag ratio as the target. Meanwhile, an accurate Fluent analysis model is established, and a comparison verification is conducted on the data with the attack angle falling within [-8.02, 12.04] and lift-to-drag ratio falling within [- 50, 100]. After Fluent modeling of the designed airfoil, the Euclidean distance between the calculated angle-lift-drag ratio data curve and the data curve tested by the wind tunnel is 0.0331, while the Euclidean distance between the simulated data in the literature and the wind tunnel data is 0.0408. It indicates that our precise model achieves 18.9% higher accuracy than the literature model. Testing and verification results indicate that our designed airfoil based on upper arc optimization and its corresponding airfoil library can meet the design requirements for the aerodynamic performance of airfoils in practical applications. It provides a valuable reference for the development of airfoil design, optimization, and generation methods. [ABSTRACT FROM AUTHOR]

Flow control has a tremendous technological and economic impact, such as aerodynamic drag reduction on road vehicles which translates directly into fuel savings, with a consequent reduction in greenhouse gas emissions and operating costs. In recent years, machine learning has also been used to develop new approaches to flow control in place of more laborious methods, such as parametric studies, to find optimal parameters with few exceptions. This paper proposes an intelligent passive device generator (IPDG) that combines computational fluid dynamics (CFD) and genetic algorithm, more specifically, the Non-dominated Sorting Genetic Algorithm II (NSGA II). The IPDG is not application specific and can be applied to generate various devices in the given design space. In particular, it creates three-dimensional passive flow control devices with unique shapes that are aerodynamically efficient in terms of the cost function (i.e., aerodynamic drag and lift). In this paper, the IPDG is demonstrated using a rear flap and an underbody diffuser as passive devices. The three-dimensional Reynolds-averaged Navierstokes (RANS) equations were used to solve the problem. Relative to the baseline, the IPDG generated flap-only, and diffuser-only provide drag reductions of 6.3% and 5.4%, respectively, whereas the flap-diffuser combination provides a drag reduction of 7.4%. Furthermore, the increase in the downforce is significant from 624.4% in flap-only to 4930% and 4595% in the diffuser and flap-diffuser combination. The proposed method has the potential to evolve into a universal passive device generator with the integration of machine learning. [ABSTRACT FROM AUTHOR]

Sailing in oblique stern waves causes a ship to make sharp turns and uncontrollable course deviation, which is accompanied by a large heel and sometimes leads to capsizing. Studying the control algorithm in oblique stern waves is imperative because an excellent controller scheme can improve the ship's course-keeping stability. This paper uses the Maneuvering Modelling Group (MMG) method based on hydrodynamic derivatives and the Computational Fluid Dynamics (CFD)-based self-navigation simulation to simulate ship navigation in waves. This study examines the effect of proportion-integral-derivative (PID) controller schemes on the stability of course maintenance based on hydrodynamic derivatives and 3DOF MMG methods. Then, the optimized PID control parameters are used to simulate the ship's 6DOF self-propulsion navigation in oblique waves using the CFD method. The nonlinear phenomena during the process, such as side-hull emergency, slamming, and green water, are considered. This study found that the range of the control bandwidth should be optimized based on the ship's heading and wave parameters. [ABSTRACT FROM AUTHOR]

In the realm of aviation, jet propulsion systems serve to provide enhanced maneuverability and to make sure that the aircraft thrust is accurately and precisely regulated during take-off and landing operations. The movement of aerodynamic control surfaces (flaps, slats, elevators, ailerons, spoilers, wing attachments) determines the mobility of practically all aircraft types. Recognized as dependable components in the aviation world for take-off and landing tasks, these control surfaces are being replaced by fluidic thrust vectoring (FTV) systems, especially in small unmanned aerial vehicles (UAVs) and short or vertical take-off and landing aircraft. The FTV system is capable of directing thrust in any preferred direction without the need for any movable components. This paper numerically examines the FTV system by utilizing computational fluid dynamics (CFD) and an optimization technique based on gradients of the system components to understand the physics of the Coanda effect in FTV systems. This research employs gradient-based optimization for nozzle design in order to optimize the parameter space for different velocity ratios (VR) by calculating the moment around the upper Coanda surface, which is used to represent the jet deflection angle. In that context, four different Coanda surface-pintle pair designs for four different VRs are produced. The parameter space shows significant improvement in all four configurations, and results reveal that all output parameters successfully delay separation on the thrust vectoring system's upper Coanda surface. Finally, four optimum design suggestions are tested at various VRs, and the most efficient and proper design is recommended based on output parameters. [ABSTRACT FROM AUTHOR]

Canard is a cutting-edge aerodynamic attachment for lowering the vehicle's drag coefficient by efficiently directing the airflow as well as reducing the lift coefficient by enhancing down-force. This paper aims to simulate the airflow crossing over the car to investigate the effect of canards' geometric design on the rear-body wake using the application of CFD-based optimization. Hence, 7 design variables based on the geometry of the canard are considered, and the objective functions are set to be drag and lift coefficients that are aimed to be minimized. Firstly, ANSYS Fluent is utilized to generate CFD calculations for a series of Design of Experiment (DOE) points. Then, the GMDH-ANN processes the results to elicit the polynomials that demonstrate the relation of design variables and objective functions. A genetic algorithm is next implemented for multi-objective optimization using polynomials as its input, and consequently, Pareto optimal points are achieved. The numerical results show that an appropriate design for canards on the rear bumper causes a potential drag and lifts reduction of 9.62% and 9.6% in comparison to the car without canards. Moreover, the size of the wake behind the car decreases and the differences in the pressure distribution between car fore-body and rear-body is reduced. Finally, the fuel efficiency is potentially enhanced due the changes in car drag coefficient and frontal area. • This paper aimed to simulate the airflow crossing over the car. • 7 design variables based on the geometry of the canard are considered. • The GMDH type of ANN is applied for the results to elicit the polynomials. • A genetic algorithm is next implemented for multi-objective optimization. • Pareto optimal points are achieved. [ABSTRACT FROM AUTHOR]

A 3D Computational Fluid Dynamics (CFD) model was set up to investigate the effects of the longitudinal slope on the risk level of users in naturally ventilated unidirectional road tunnels in the event of a fire accident. These tunnels, which in general do not require any mechanical ventilation system, have a length <1 km and their natural ventilation is due to the difference of pressure at the portals and/or the piston effect of the unidirectional traffic flow. Fire accidents related to vehicles characterized by different maximum Heat Release Rates (HRRs max), situated at different locations from the entrance portal of the tunnel, were simulated by varying the longitudinal slope (i), as well as by applying both a positive and negative pressure difference (ΔP) between the entrance and exit portals to also consider any adverse wind conditions, or neglecting that (i.e., ΔP = 0). The combined effects of Peak Hourly Volumes (PHVs) were also investigated in the Quantitative Risk Analysis (QRA), which based on a probabilistic approach, considered as a risk indicator the annual cumulative frequency (F) of having a certain number of potential fatalities (N). The longitudinal profiles of temperature, radiant heat flux, toxic gases concentrations, and visibility distance upstream of the burning vehicle along the escape route (i.e., sidewalks) are reported and compared with the acceptability limits to verify if the environmental conditions are tolerable for user safety while escaping from the tunnel towards the entrance portal or the emergency exit located in the middle of the tunnel length. The results showed that the number of dangerous scenarios for user safety increased in the event of adverse wind (i.e., ΔP < 0) and/or negative gradients (i.e., i < 0). The QRA indicated the combinations of i, ΔP , and PHV for which the annual cumulative frequency (F) of having a given number of potential fatalities (N) was not acceptable. By providing additional points of knowledge in the field of fire safety engineering, this paper might serve in the design of the vertical alignment of naturally ventilated tunnels with a length <1 km, as well as in the strategies of management and traffic control. • The paper investigates user safety in the event of fire in road tunnels, a computational fluid dynamics modeling is set up. • The effects of the longitudinal slope, pressure difference between the tunnel portals, and traffic volume are considered. • The results show that the worst scenarios are for adverse wind and negative gradients. • The number of dangerous scenarios for user safety increases in the presence of adverse wind and negative gradients. • For a given pressure difference and/or longitudinal slope, the risk level for users increases with the traffic volume. [ABSTRACT FROM AUTHOR]

Flow dynamics accurate prediction is critical for the early-stage design and performance optimization of the piezoelectric (PZT) printhead. To achieve this, the Computational Fluid Dynamics (CFD) method has been widely used. However, for accurate fluid simulation of the PZT printhead, the optimal parameters settings still need to be clarified, which will be discussed in full in this paper. The modelling work is divided into two subparts, namely, a three-dimensional (3-D) modelling for the ink chamber and a two-dimensional (2-D) modelling for the nozzle-air domain. Simulations of the 3-D ink chamber were carried out firstly, thereby the transient mass flow rate of the ink outflow from the chamber could be obtained, which will be set as the inlet boundary condition of the 2-D nozzle-air simulations. To ensure accuracy and convergence of 2-D simulations, independence tests of the mesh grid and time step were performed, where the Fine level mesh density and 1e-8 s time step were identified as the optimal choice. And this combination was adopted in the transient simulations of the droplet ejection process. For the model validation purpose, an experimental test rig was developed, and comparisons between the simulations and experimental tests show a good agreement, verifying the accuracy of the developed model. In addition, to validate the feasibility of the developed model, the effect of the ink viscosity on the droplet ejection process was tested, and the results were consistent with those produced by published literature, confirming the feasibility of the CFD model developed in this paper. [ABSTRACT FROM AUTHOR]

The worldwide lethal prevalence of atherosclerotic diseases has made it a crucial topic of research, the descending aorta is a major artery with complex geometry involving curvature, branches, and bifurcation leading to common iliac arteries. This paper aims to scrutinize the intricate blood flow patterns and the flow parameters with the increasing degree of stenosis in the infrarenal aorta, which has been accomplished through computational fluid dynamics modeling. A 3D CAD model of the healthy aortoiliac bifurcation was constructed from MR images, and three diseased models with 32%, 47%, and 71% occlusion in the infrarenal aorta region were constructed. At the inlet, pulsatile velocity and at the outlet pressure boundary conditions were applied, blood was considered Newtonian and turbulence was modeled using Large Eddy Simulation (LES). The numerical simulation was carried out using finite volume method on ANSYS. The predicted hemodynamic parameters like velocity, wall shear stress (WSS), oscillating shear index (OSI), Q-Criterion and turbulence intensity were post-processed for all the models, the analysis of which provides an insight into the myriad processes involved in the inception and evolution of atherosclerosis. The transition of blood flow from laminar to turbulent with increase in the degree of stenosis is a very eminent feature of this study, turbulence is identified in cases with 47%, and 71% occlusion and is dominant in the latter. [ABSTRACT FROM AUTHOR]

Microchannel heat sinks are very widely used due to their high heat transfer coefficients and low refrigerant requirements. Nevertheless, microchannel heat sinks still perform sub-optimally when it comes to thermal performance. Therefore, this paper investigates the individual and combined impacts of different characteristics of porous media on the thermal performance of microchannel. Four porosity values are considered: 0.8, 0.85, 0.9, and 0.95. The evaluation is based on three-dimensional computational fluid dynamics simulations. Due to the large number of degrees of freedom in this study, Constructal Theory and Design of Experiments are employed. In this study, the response surface type is Genetic Aggregation, while the Latin Hypercube Sampling algorithm is used for data sampling and Genetic algorithm is used for optimization. Combining porous layers with microchannel heat sinks reduces maximum temperatures about 3K. It is also observed that a lower maximum surface temperature is achieved in the cases with less porosity. Furthermore, the optimal geometry and size of the microchannels with porous layers are determined. [ABSTRACT FROM AUTHOR]

This paper provides 2D Computational Fluid Dynamics (CFD) investigations, using OpenFOAM package, of the unsteady separated fully turbulent flows past a NACA 0015 airfoil undergoing sinusoidal pitching motion about its quarterchord axis in deep stall regime at a reduced frequency of 0.1, a free stream Mach number of 0.278, and at a Reynolds number, based on the airfoil chord length, 𝑐, of 1.95 × 106. First, eighteen 2D steady-state computations coupled with the 𝑘 − 𝜔 SST model were carried out at various angles of attack to investigate the static stall. Then, the 2D Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations of the flow around the oscillating airfoil about its quarterchord axis were carried out. Three eddy viscosity turbulence models, namely the Spalart-Allmaras, Launder-Sharma 𝑘 − 𝜀, and 𝑘 − 𝜔 SST were considered for turbulence closure. The results are compared with the experimental data where the boundary layer has been tripped at the airfoil’s leading-edge. The findings suggest that the 𝑘 − 𝜔 SST performs best among the other two models to predict the unsteady aerodynamic forces and the main flow features characteristic of the deep stall regime. The influence of moving the pitching axis downstream at mid chord was also investigated using URANS simulations coupled with the 𝑘 − 𝜔 SST model. It was found that this induces higher peaks in the nose-down pitching moment and delays the stall onset. However, the qualitative behavior of the unsteady flow in post-stall remains unchanged. The details of the flow development associated with dynamic stall were discussed [ABSTRACT FROM AUTHOR]

Simulation, as a pillar technology of Industry 4.0, is a key tool for improving manufacturing processes. Simulation is an indispensable set of technological tools and methods for the successful implementation of digital manufacturing, since it allows for the experimentation and validation of product, process, and system design and configuration. The value of simulation is evident, especially in today's volatile manufacturing environment, which is influenced by globalization and ever-increasing demands for higher levels of product customization and personalization. Moreover, a significant manufacturing issue is the interoperability and communication among the several simulation tools. To that end, an Industrial Internet of Things (IIoT) framework for simulation and visualization of selected monitored values based on Mixed Reality (MR) and Computational Fluid Dynamics (CFD) in a cloud-computing environment for intuitive data visualization on smart devices is presented in this paper. As such, in light of the possibilities offered by digital technologies such as CFD simulation, smart factories can gain a competitive advantage because of the low cost, low risk, and the provided useful insights. The range of CFD applications encountered in process manufacturing and engineering varies greatly depending on the industry. Summarizing, this review paper identifies the gaps in current practices, and future trends and challenges to be met on the field are outlined. The contribution of the research work extends to the proposal of a workflow for the integration of Mixed Reality (MR) to the CFD simulation, in an attempt to create simulation holograms on the user's field of view. [ABSTRACT FROM AUTHOR]

This paper investigates modelling strategies on the prediction of lift and drag coefficients of a NACA0012 airfoil at Reynolds number of 360,000. Two computational methods are employed; namely Navier-Stokes equation and panel method, by using different tools for computing lift and drag coefficients. The obtained results are compared against experiment in order to assess the accuracy of each technique. Two turbulence models are employed; Reynolds stress model, which is not based on Boussinesq assumption and accounts for flow anisotropy and realizable model which is based on the Boussinesq assumption for computing Reynold stresses. Grid independent solution is produced using the 2-D URANs by employing the fitting method and the obtained lift and drag coefficients are compared against experiment. The fitting method is found to be efficient in saving computational time and power. It is also found that Boussinesq approximation is efficient in predicting lift coefficient. However, the 3rd order panel method produced a remarkably accurate drag coefficient compared to other investigated computational models. Combining the findings of this paper with the existing computational methods in the literature would significantly in improve the accuracy of predicting lift and drag coefficients and may significantly enhance the accuracy of simulation of several aerodynamics applications. [ABSTRACT FROM AUTHOR]

For diesel engines equipped with a combined spiral/tangential inlet, the main object of the valve structure and valve lift dissimilitude strategies is the valve, the changes of both will alter the motion state of the in-cylinder airflow, which has an important impact on the formation and combustion of the mixture. In order to investigate the flow performance of valve structure and valve lift dissimilitude, this paper used computational fluid dynamics (CFD) numerical simulation and multi-parameter regression methods to optimize the dual intake valve structure and obtained three valve structures with better intake performance first. Then, the optimized intake valve structure models were combined with the valve lift dissimilitude schemes to conduct steady-flow tests for the intake port. Through the reasonable combining of the two, the intake performance of the original engine was further improved. The results show that the valve structure has a relatively small influence on the intake mass, while it has a greater effect on the formation of the swirl in the cylinder, increasing the swirl ratio by 8.0%. The optimized valve structure model was combined with the valve lift dissimilitude scheme. It was found that the valve structure with optimal intake mass combined with the dissimilitude scheme of the largest valve lift of the spiral inlet could increase the flow coefficient by a maximum of 1.9%. The valve structure of the optimal swirl ratio combined with the dissimilitude scheme of the largest valve lift of the tangential inlet could increase the swirl ratio by a maximum of 9.7%. This study can guide diesel engines with combined intakes to increase the intake mass and improve the intake performance. [ABSTRACT FROM AUTHOR]

Turbocharger systems enhance the engine power and efficiency, reduce its pollution, and downsize the engine volume. As the significance of exploiting turbochargers in gasoline engines is surging among automobile manufacturers, the necessity of improvement in the system components becomes more critical. This paper investigates the impacts of a turbocharger turbine bypass and wastegate geometry alterations on the performance and the flow field characteristics via numerical simulations. The numerical method verification and mesh independence study are performed for the original geometry. The simulation results of the altered geometries indicate that better alignment between the bypassed and the bulk flows leads to higher efficiency of the turbocharging system. In addition, the bent or elbow-shaped and protruded turbine walls immediately downstream of the wheel are found to be unfavorable. It is also uncovered that if the wastegate shape and the housing walls are designed in such a way that the effects of ensuing vortices are minimized, it improves the stage efficiency, which is desirable for two-stage turbochargers. Furthermore, a novel manufacturable design is proposed in this study, which increases the efficiency and useful power by 19.9% and 6.7%, respectively. [ABSTRACT FROM AUTHOR]

The separation efficiency and pressure drop of the dynamic separator of cement particles can be affected by many factors, like structural type, geometric parameters, and operating characteristics. In this paper, CFD modeling is applied to investigate the fluid flow behavior and the efficiency of the industrial dynamic separator with different heights of the inner cone called the vortex breaker. Simulations are based on the RSM and the DPM models. A CFD comparison of the original design and new designs has been performed. The simulation results showed that the fluid flow inside the industrial air separator is greatly dependent on the height of the vortex breaker. Interesting phenomena were observed by the numerical simulations and the results revealed that an increase in the height of the vortex breaker up to three-quarters of the magnitude of the fine powder outlet duct can improve the performances of particle separation not only by reducing 29% the cut size, and by 40% the bypassing of fine particles but also by increasing 30% the separation sharpness while keeping the pressure drop substantially unchanged. [ABSTRACT FROM AUTHOR]

The Dual Bell Nozzle is the most ambitious of several supersonic, altitude-compensating nozzle concepts for rocket engines. This design's objective is to enhance performance in two different evolving regimes (Sea-Level and High-Altitude Mode) by self-adaptation with no mechanical control. The concept is simple in theory, but the structural efforts involved are significant. The study carried out in this paper is a simulation of the flows in this type of nozzle. Computational fluid dynamics (CFD) is increasingly used as an analytical tool in research and industry. Simulation is not a substitute for experimentation but a complement to it; it allows the analysis of the problem in real conditions (reproduce tests that are done in experimentation to better understand them and at lower cost) or, on the contrary, in extreme or marginal test conditions (extreme climates, installation defects, etc.). Through simulation, the studied system becomes more flexible. We can easily make parametric studies. Simulation almost always takes the form of a program or computer tool. These are commonly called simulation environments. Developments and progress over the past two decades have led to the emergence of a methodology that has become standard. As for any complex system, the control of a phenomenon is based on the identification and modularization of the tasks. Currently, the standard methodology divides the simulation process into four distinct tasks: geometric modeling, meshing, solving, and finally analysis and visualization. In this study, we will present a test case used to validate our computational models that will be used to optimize the profile of a dual bell nozzle. We will use the Ansys-ICEM environment to generate the meshes and the Ansys-Fluent environment to solve the equations of our models. Our results will then be compared with experimental and numerical data from our literature review. [ABSTRACT FROM AUTHOR]

This paper aims to enhance the performance of H-Darrieus Vertical Axis Wind Turbine (VAWT) via introducing upstream deflectors. The impact of this addition has been investigated and discussed through different deflector configurations. The turbine performance before and after adding different wind rotor barriers was compared. A two dimensional, incompressible, transient, and turbulent flow model was built up in order to simulate the air flow around the turbine blades. Model verification and validation were performed through comparing the model solutions using different mesh sizes, time steps, turbulent models, and discretization schemes. Computational Fluid Dynamics (CFD) models were validated to provide novel insights on the effect of the deflectors on the aerodynamic characteristics of a VAWT blades. Results showed that the presence of a single deflector increases the highest value of the moment coefficient of the bare configuration by 24%, either increases the negative torque values, while two defectors increase the maximum value by 22% and the overall average value of the moment coefficient over the optimal range for the tip speed ratio. [ABSTRACT FROM AUTHOR]

Raising rotational speed and operating pressure is an effective way to increase the power density of axial piston pumps. However, the axial piston pump with standard hollow pistons suffers from problems of volumetric losses, pressure ripple, and cavitation at high rotational speed and operating pressure. To reduce these fluid-related problems, the capped piston design is a promising alternative to the standard piston design by minimizing the dead volume. The capped pistons have been applied in commercial axial piston pumps but it remains unclear how the flow characteristics of axial piston pumps benefit from them. Therefore, this paper aims to clarify the mechanism of capped pistons in improving the flow characteristics of axial piston pumps. A computational fluid dynamics model is developed to compare the pump's flow characteristics between standard and capped pistons. The simulation results show that compared with the standard hollow pistons, the capped pistons can significantly reduce the compressibility effects, pressure ripple, and cavitation over a wide range of operating conditions. [ABSTRACT FROM AUTHOR]

To reduce the noise in a pump piping system and increase the usage time of equipment, a new type of porous muffler is proposed in this paper. A water guide cone is incorporated into the muffler structure, which may help to redirect the fluid media in the piping system. The porous structure is adapted from a muffler shell, water cone wall and round bottom plate. According to this structure, the muffler sample is made, and a pump pipeline system test bench is set up. The outlet noise of the pump pipeline system is measured after installing the muffler. At the same time, the muffler is numerically simulated by combining computational fluid mechanics and Lighthill acoustic theory. The characteristics of the flow field and external sound field under three different flow conditions of 200 m³ /h, 400 m³ /h and 600 m³ /h are assessed. The numerical simulation results show the same dominant frequency and trend as the experimental results. The rationality of the numerical simulation is verified. Research shows that: the level of sound pressure at the muffler's outlet is lower than at the inlet, causing muffling, and the characteristics of a quadrupole sound source appear at the outlet. The proposed muffler has a certain effect in reducing noise in the pump pipeline system. [ABSTRACT FROM AUTHOR]

Accurate predictions of the near wake of horizontal-axis wind turbines are critical in estimating and optimizing the energy production of wind farms. Consequently, accurate aerodynamic models of an isolated wind turbine are required. In this paper, the steady-state flow around an experimental horizontal-axis wind turbine (known as the MEXICO model) is investigated using full-geometry computational fluid dynamics (CFD) simulations. The simulations are performed using Reynolds-Averaged Navier-Stokes (RANS) equations in combination with the transitional k-kl-ω turbulence model. The multiple reference frame (MRF) approach is used to allow the rotation of the blades. The impacts of the nacelle and blade rotation on the induction region and near wake are highlighted. Simulation cases under attached and detached flow conditions with and without the nacelle were compared to the detailed particle image velocimetry (PIV) measurements. The axial and radial flow behaviors at the induction region have been analyzed in detail. This study attempts to highlight the nacelle effects on the near wake flow and on numerical prediction accuracy under various conditions, as well as the possible reasons for these effects. According to simulation results, the rotation of blades dominates the near wake region, and including the nacelle geometry can improve both axial and radial flow prediction accuracy by up to 15% at high wind speeds. At low wind speeds, the nacelle effects can be ignored. The presence of the nacelle has also been shown to increase flow separation at the trailing edges of the blade airfoils, increasing both root and tip vorticities. Finally, small nacelle diameters are recommended to reduce flow separation on the blades and increase the average velocity downstream of the rotor, thereby optimizing wind farm output power. [ABSTRACT FROM AUTHOR]

In this paper, the behavior of blood flow through several consecutive and relatively close clogs inside the vessel is investigated by modeling blood vessels. The used clogs are dual-channel and single-channel currents, which are naturally very close. Consecutive clogs with equal intervals and different clogs of 30%, 50%, and 70% are considered. The inflow to the clogged area is in the form of a real pulse, the same as the pulse of blood flow in a vein. For this purpose, the Navier-Stokes equations are solved numerically in an unstable state, while the continuity equation in the capillary coordinate system is solved by the numerical method. The distribution of flow velocity and distribution of shear and vertical stresses in the vessel wall in three states of the flow cycle are related to the acute conditions of the cyclic blood flow. The results show that the rate of increase in shear stresses and the rate of decrease in vertical stresses become much more severe upon increasing the rate of clamping. These changes are more severe at distances of 17 mm for two channels and 25 mm for single channels, which have a maximum blood flow rate. [ABSTRACT FROM AUTHOR]

This paper discusses the experimental studies performed on a single closed loop pulsating heat pipe (CLPHP) to evaluate its thermal performance. The pulsating heat pipe is brass which has a single closed loop. Aluminium oxide (Al2O3) and deionized (DI) water nanofluid were utilized as working fluids, with different volume concentrations of aluminium oxide nanoparticles of 0.05 %, 0.5 % and 1%. The aluminium oxide particles are mixed with water in the two-step method to produce a stable suspension. Experiments are carried out in the horizontal mode with watt loads of heat inputs ranging from 10 w to 100 w. The temperature differences between the evaporator and condenser portions, thermal resistance, heat transfer coefficient and thermal conductivity are the parameters used to determine thermal performance. The thermal resistance of aluminium oxide and DI water nanofluid was the lowest, having 48 % less than that of water. The effective thermal conductivity of the heat pipe improves as the concentration of nanoparticles increases. The comparison between experimental results and computational fluid dynamics (CFD) simulation results CLPHP was carried out under the same condition. [ABSTRACT FROM AUTHOR]

This paper investigates the flow structures on the near- and far-wake of a 1/8th scaled simplified heavy vehicle model called Ground Transportation System (GTS) model using a steady-state Reynolds-averaged Navier- Stokes (RANS) with k-ω Shear Stress Transport (SST) turbulence model at Reynolds number (Re) of 1.6 × 106 and yaw angles (Ψ) = 0o-14o. The current CFD results have been validated using experimental data from the literature. Two crosswind conditions based on the crosswind incidence angle (β) are adopted; β < 90o is called crosswind, and β = 90o (perpendicular to the GTS side surface) is called pure crosswind. Vortex detection scheme based on Ω method and total pressure coefficient (Cpt) contours is used to visualize the wake structure. With Ψ, vortices on the GTS roof take birth as a result of pressure differences between the windward and leeward sides. These vortices grow in size as they travel downstream. The growth in size is related to the Helmholtz theorem of vorticity and Kelvin's Circulation Theorem. The vortices merged at Z/W > -4 (Z/W = 0 is the GTS rear surface) downstream of the GTS for Ψ = 7.5o and 14o. The merged vortex dissipates at Z/W > - 6 and Z/W > -8 for Ψ = 7.5o and 14o, respectively. In the pure crosswind condition, the merged vortex attaches to the ground due to the velocity difference between the freestream and the moving computational ground used in the present simulation. At Ψ = 14o, surface streamlines on the GTS surface show the creation of two corotating vortices on the windward roof. For the present Ψ, similar flow structures between the two crosswind conditions are shown. Initial results show that the aerodynamic crosswind stability of a truck is related to the spanwise pressure difference between the windward and leeward surfaces of the truck. [ABSTRACT FROM AUTHOR]

Small underwater vehicles have unique advantages in ocean exploration. The resistance and volume of a vehicle are key factors affecting its operation time underwater. This paper aims to develop an effective method to obtain the optimal hull shape of a small underwater vehicle using Kriging-based response surface method (RSM) and multi-objective optimization algorithm. Firstly, the hydrodynamic performance of a small underwater vehicle is numerically investigated using computational fluid dynamics (CFD) method and the value range of related design variables is determined. The mesh convergence is verified to ensure the accuracy of the calculation results. Then, by means of the Latin hypercube sampling (LHS) design of simulation, the Kriging-based RSM model is developed according to the relation between each design variable of the vehicle and the output parameters applied to the vehicle. Based on the Kriging-based RSM model, the optimal hull shape of the vehicle is determined by using Screening and MOGA. As results, the vehicle resistance reduces and volume increases obviously. [ABSTRACT FROM AUTHOR]

The emphasis of this paper is on challenges in simulation of cavitating flows, especially flows around propeller and rudder. First the sources of errors in predictions based on Computational Fluid Dynamics (CFD) are highlighted: the accuracy of geometry, grid quality and fineness, turbulence modeling and cavitation modeling. The interaction between errors from different sources is also discussed. The importance of turbulence in the flow upstream of propeller and the difficulty of accounting for it is described next. Special attention is paid to the prediction of tip-vortex cavitation and to scale effects. Results from simulations are compared to experimental data from SVA Potsdam, except for the full-scale analysis of flow around hull, propeller and rudder, for which no experimental data is available. It is concluded that cavitation can be predicted to a degree which makes simulation an indispensable tool for design and optimization of maritime vessels. [ABSTRACT FROM AUTHOR]

The regulating valve applied in coal liquefaction systems becomes seriously worn and its service life decreases because of a significant difference in pressure and solid-liquid flow. This study proposes a wear-resistant multistage pressure relief string-regulating valve, and examines the characteristics of depressurization of flow and the erosion of its throttle element by using computational fluid dynamics (CFD) simulations and the discrete element method (DEM) combined with the E/CRC (Erosion/Corrosion Center) erosion model of the WC-Co coating. The influence of different sizes of the opening of the valve and varying differences in pressure on the characteristics of erosion is analyzed. Moreover, properties of collisions between particles (such as the particle impact velocity and mass per second) are used to represent and analyze the characteristics of erosion. The numerical results show that the cylinder, flat, and bevel of the valve are at high risk of erosion. The characteristics of erosion of the multistage pressure relief string-regulating valve studied in this paper can provide a reference for optimizing methods of erosion prevention. [ABSTRACT FROM AUTHOR]

Insertion of large objects or intruders into granular material is common both in nature and industrial applications. During penetration due to collision between intruder and granular particles, intruder experiences resistance or drag force (analogy from fluid). In literature, it is extensively studied that in dry packed beds granular drag force increases with the intrusion depth. However, nearly no information is available about the effect of fluidization on the granular drag force and is the main theme of this paper. In this paper, discrete element method (DEM) and computational fluid dynamics (CFD) is used for performing numerical simulations. Simulations showed that granular drag force becomes independent of intrusion depth at incipient fluidization and is a function of Reynolds number. Using the mathematical relation of fluid drag force, granular viscosity of the fluidized bed is calculated. The physics for the fluid like state of granular material and the independence of granular drag force with intrusion depth is explained at the end of paper. [ABSTRACT FROM AUTHOR]

The paper analyzes the possibility of improving the efficiency of the propeller as one of the main directions of improving the main propulsion plant. The requirements of the MARPOL-73 convention, as amended, and the need to adapt the main propulsion plant to changing operating conditions require improving the design of the fixed pitch propeller. The paper presents the results of CFD modeling and studies of the flow around the NACA-2412 blade with the supply of additional medium along the chord, regarding the suction surface. This work is an adaptation of the method used in aviation for increasing lift force by blowing the boundary layer. The magnitude of the lift force has a significant impact on the dynamic characteristics of the propeller. CFD modeling of the propeller blade profile in compressible and incompressible media, and also the calculation of the parameters of the NACA-2412 profile with the supply of additional medium were performed. The modeling results are confirmed by comparison with known modeling results for compressible media and experimental data. The possibility of increasing the efficiency of the propeller due to the jet supply of additional water to the suction surface of the blade along the chord has been proved. The results of the work can be used to control the operating mode of the main engine by changing the thrust and the hydrodynamic torque of resistance to rotation of the propeller. [ABSTRACT FROM AUTHOR]

The dispersion of hazardous gas in the environment presents dangerous risks for people living close to chemical plants or storages. Since heavy gases tend to stay at lower levels and disperse at a slower pace in the atmosphere, they are potentially more dangerous. In this paper, various mathematical models for turbulence (including k-ε, RNG k-ε, EARSM, LES, DES) and their associated parameters have been assessed, compared and validated against the experimental data in various scenarios to find the most suitable one for atmospheric dispersion of dense-gases. This topic has been investigated and validated by a computational fluid dynamics (CFD) simulation of the Kit-Fox experiment. The precision of the CAD models, practicality, computational resource requirements, and some other factors have been considered and addressed in this paper to achieve a comprehensive solution for atmospheric dispersion. The results here suggest that the proper selection of the turbulence model and the turbulent Schmidt number is crucial. Our results indicate that the most promising combination in the case of atmospheric dense-gas dispersion is the RNG k-ε model with the Schmidt number of 0.4, considering the demand for accuracy and computational resource. [ABSTRACT FROM AUTHOR]

Aquatic animals usually generate the effective propulsive force via non-sinusoidally flapping their fins. Inspired by the kinematics of fish, the propulsive characteristics of a NACA012 hydrofoil is numerically studied in this paper. The combination of non-sinusoidal heaving and pitching motions is adopted in the twodimensional hydrofoil kinematics parameters. The elliptic function and the flattening parameter S are introduced to achieve the varieties of non-sinusoidal periodic motions. The numerical model is established by using the commercial computational fluid dynamic solver STAR-CCM+, and the code is verified by comparing with the published experimental results. The Reynolds number is fixed at 40,000 in all the numerical simulations. The results show that the non-sinusoidal trajectories affect the propulsive performance by affecting the angle of attack (AOA), the hydrodynamics of the foil and the flow structure behind the foil. The non-sinusoidal flapping trajectories can improve significantly the thrust coefficient at the same kinematics parameters compared with the sinusoidal motions in most cases. However, they may reduce the propulsive efficiency. When the values of S are greater than 1, the improvement of thrust coefficient acquired with the non-sinusoidal motions is more obvious. The wake pattern is also discussed which indicates that the strong leading-edge vortices results in the decrease of the propulsive efficiency acquired by the nonsinusoidal trajectories. It is possible to apply the non-sinusoidal motions of a flapping foil to improve propulsive performance of the underwater bionic machine. [ABSTRACT FROM AUTHOR]

Based on the principle of two-phase hydrodynamics and the mechanism of cavitation generation, this paper uses the finite volume method (FVM) in computational fluid dynamics (CFD) to analyse the features of fluid flow in jet amplifier, i.e., the pilot stage of jet pipe servo valve, and designs a lab bench to experimentally prove the accuracy of this numerical method. On this basis, the author discussed how four structural parameters influence the amplification efficiency of the jet amplifier. The amplification efficiency of the jet pipe servo valve can be maximized by setting the distance between nozzle and receiving holes of 0.1 mm, the diameter of receiving holes of 0.2 mm, the inclination angle of 22.5°, and the spacing between the two receiving holes of 0 mm (if possible). The research methods and results provide a solid basis for the design and performance prediction of the jet pipe servo valve. [ABSTRACT FROM AUTHOR]

This proposition presents study and assessment of execution and optimal arrangement of power exchangers and force exchangers association. The survey consolidates a simulational assessment of fluid stream in case and chamber heat exchanger, premium arrangement of case and chamber heat exchanger and single pass case and chamber heat exchangers, and progression of force exchanger associations. In the simulational assessment of fluid stream in case and chamber heat exchanger a couple of extraordinary limits would be participated to get various plots of entertainment. Considering simulational data, connections for separating and finding out heat move coefficients and strain diminishes, temperature change and speed points have been gained with great accuracy. This exploration paper centers around the representation of different boundaries, for example, speed, strain and temperature varieties along in a cross stream type case and chamber heat exchanger. [ABSTRACT FROM AUTHOR]

Design and analysis of subsonic open wind tunnel by using Computational Fluid Dynamics at different inlet velocities is carried out in this paper. The governing equations of fluid flow were solved numerically to calibrate the wind tunnel using computational fluid dynamics method by considering the flow as steady, incompressible, turbulent and three dimensional. To obtain a robust numerical simulation, coupled algorithm is used for pressure-velocity coupling with second order and second order spatial discretization to solve all the governing equations involved. [ABSTRACT FROM AUTHOR]

Abstract Hybrid optimization algorithms which combine Evolutionary Algorithms (EAs) and Gradient-Based (GB) methods o refine the most promising solutions, are valuable tools for use in engineering optimization. Several hybrid methods can be found in the literature; differences among them are associated with the criteria used to select individuals for refinement through the GB method and the feedback the EA gets from the latter. GB methods require the gradient of the objective functions with respect to the design variables. By employing the adjoint method in problems governed by partial differential equations, the cost of computing the gradient becomes independent of the number of design variables. For multi-objective optimization problems this paper is exclusively dealing with, the availability of the gradients of all objective functions is not enough. Hybrid algorithms require the computation of descent directions in the objective space capable of improving the current front of non-dominated solutions. Using the sum of weighted objectives as the new objective function is ineffective. In this paper, a method which refrains from using arbitrarily defined weights is proposed. The method is driven by data obtained from the Principal Component Analysis (PCA) of the objective function values of the elite individuals at each generation of the EA. The PCA, with computational cost that of the solution of an eigenproblem, identifies the direction in the objective space along which the current front of non-dominated solutions should be improved. This along with the gradients computed by the adjoint method are used by the GB method to refine selected individuals. The efficiency of the proposed hybrid algorithm is further improved by employing online trained surrogate models or metamodels and Kernel PCA within the EA-based search. The proposed method is demonstrated in aerodynamic shape optimization problems, using in-house Computational Fluid Dynamics software and its adjoint. Highlights • Hybrid Multi-objective Optimization combining EAs and a gradient-based method. • PCA computes the Pareto Advancement Direction improving the Pareto front. • An efficient EA, assisted by Metamodels and Kernel PCA, can further be improved. • Gradient computation is assisted by the continuous adjoint method in CFD. • Method validation in three multi-objective aerodynamic shape optimizations. [ABSTRACT FROM AUTHOR]

This paper proposes a method for optimising the hull form of ocean-going trawlers to decrease resistance and consequently reduce the energy consumption. The entire optimisation process was managed by the integration of computer-aided design and computational fluid dynamics (CFD) in the CAESES software. Resistance was simulated using the CFD solver and STAR-CCM+. The ocean-going trawler was investigated under two main navigation conditions: trawling and design. Under the trawling condition, the main hull of the trawler was modified using the Lackenby method and optimised by NSGA-II algorithm and Sobol + Tsearch algorithm. Under the design condition, the bulbous bow was changed using the freeform deformation method, and the trawler was optimised by NSGA-?. The best hull form is obtained by comparing the ship resistance under various design schemes. Towing experiments were conducted to measure the navigation resistance of trawlers before and after optimisation, thus verifying the reliability of the optimisation results. The results show that the proposed optimisation method can effectively reduce the resistance of trawlers under the two navigation conditions. [ABSTRACT FROM AUTHOR]

The edge base bleed type is presented in this paper. Based on the advantages of computational fluid dynamics and the firing range prediction of base bleed projectile, the flight ballistic of base bleed projectile with two kinds of base bleed type is solved by using the computational aerodynamics coupled with particle trajectory, obtained the change laws of operation parameter, flow filed of base bleed projectile with time. The results show that: The performance of the edge base bleed type is better than that of the traditional center base bleed type, and the fire range of the base bleed projectile with edge type is about 2 km higher than that of the center type. The base bleed parameter of the two kinds of base bleed type at the state of drag reduction increase first and then decrease with the increase of time. For the center base bleed type, the drag coefficient increases with time. For the edge base bleed type, the drag coefficient is nearly stable at the reduction state, and is always smaller than that of the center base bleed type. The base flow structure of the edge base bleed type does not change with both the time and base bleed parameter. The base bleed gas always forms the main recirculation zone at the bottom of projectile and plays the role of drag reduction. [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]

Sinusitis disease has become widespread lately. Warming the sinus area with a face mask may prevent sinusitis disease, which may occur due to the presence in a place colder than body temperature especially on a cold morning day. This paper proposes experimentally the creation of a transparent facemask prototype that can maintain warmth in both the maxillary and frontal sinus areas. It contains an overlap volume to improve temperature, CO 2 and H 2 O comfort. Furthermore, a two-dimensional numerical study is provided by Ansys® FLUENT 2020 R1 Computational Fluid Dynamics (CFD) simulations using RNG (ReNormalization Group), k-ɛ turbulence model. It predicts flow characteristics of velocity, temperature, and mass fraction of CO 2 and H 2 O distributions during 28 breathing cycles. This approach is validated by comparing its results with previous studies and the experimentally measured results for temperature using an Arduino Temperature sensor at a selected point within the experimental prototype. The mean temperature values rise to reach a steady-state for both numerical and experimental study. The CO 2 and H 2 O concentrations inside the mask are very small. The results confirm that the mask achieves its purpose in warming nasal and sinus areas. [ABSTRACT FROM AUTHOR]

This paper investigates the improvement of the bow region of the trimaran ship hull, and proposes a Computational Fluid Dynamics (CFD)-based automated method to reduce total resistance. The main objectives pursued in the present study include: 1) to create and develop a useful optimization platform to modify the ship hull and 2) to investigate the effect of different inverted bow on the hydrodynamic performance of trimaran ship. A wave-piercing bow trimaran hull was taken as the baseline design. The ship bow has been redesigned using Arbitrary Shape Deformation (ASD) technique, which defines the input variables for the optimization process. The objective function was the drag force, and this study is conducted at cruise speed. To accomplish this task, two optimization methods were sequentially applied. A Latin Hypercube Sampling tool distributes design points and an Radial Basis Function (RBF)-based surrogate model is constructed to investigate system behavior. The final optimum design of Design Of Experiment (DOE) study was introduced to the direct optimization SHERPA algorithm as a baseline design. The integration of CFD solver, geometric parameterization and optimizer tools is managed by the HEEDS MDO software package using a multi-connection method. The optimization results show that the optimization was successfully carried out and the resistance was reduced by 10.2%. The comparison between the initial hull and the optimized hull shows that the proposed optimization platform can be used for ship hull optimization in industrial application and significantly reduces the computational time and workload. [ABSTRACT FROM AUTHOR]

The operating range of centrifugal pumps is a very important information for the long service life and risks regarding various premature failures. The pump cannot always operate within the permitted range, for example, it must start and shut down the operation. When developing and selecting a pump, it is necessary to take into account the fact that the pump should be operated close to the best efficiency point (BEP) as often as possible. In this paper, we discuss the kinematic causes for the formation of the so-called hump zone in the pump H(Q) characteristic, where the flow rates are smaller than at the BEP. For the case of a reversible pump turbine, the detailed course of the pump characteristic at different relative openings of the guide vanes was numerically analyzed. The article presents the detailed flow field of velocity vectors and streamlines in front of the runner, inside the runner, and behind the runner. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the combustion and turbulence Sub-Grid Scale (SGS) model on simulation of a pool fire turbulence field has been studied in open source Cumputational Fluid Dynamic (CFD) software, OpenFOAM. Two combustion models: Eddy Dissipation Model (EDM) and infinite fast chemistry, with the one-equation and Smagorinsky SGS model, are evaluated for a large-scale pool fire. In general, fast kineticbased combustion models predict excessive heat release rate. The mean squared of the velocity uctuations is over-predicted. In this simulation, the turbulence models have no significant effect on the results. In fact, the effect of the combustion model is dominant. The EDM combustion model is more compatible when used with the one-equation SGS model and improves the results compared to other cases. In addition, the infinite fast chemistry combustion model is not a suitable model for fire simulation. [ABSTRACT FROM AUTHOR]

Data-driven deep learning approach heavily relies on the diversity and quantity of data. Acquiring data in the computational fluid dynamics (CFD) domain is a time and computationally intensive process. This paper proposes a semi-supervised learning method called discriminative regression fitters (DRF) for aerodynamic prediction of airfoils. DRF utilizes neural networks' memory property to dynamically divide pseudo-labeled data into easy and difficult subsets using a model of Gaussian distribution. The method classifies unlabeled data based on loss and updates the pseudo-labeled data, improving the model's generalization capability. Experiments on airfoil regression task datasets show that DRF achieves similar or better prediction accuracy than fully supervised approaches. It reduces data acquisition time by 70%. Ablation studies and qualitative results verify the effectiveness of DRF. The surrogate model obtained from DRF is extended to airfoil optimization, demonstrating its practicality. DRF provides a promising direction for improving the regression task while reducing the reliance on large amounts of CFD data. • A semi-supervised learning-based DRF method is proposed. • DRF employs the memory properties of the network to improve generalizability. • DRF significantly reduces the time required to acquire datasets by 70%. [ABSTRACT FROM AUTHOR]

Despite enormous advances in computer power, computationally costly models impede the use of traditional optimization approaches that must be invoked repeatedly during the optimization process in practical engineering applications. Surrogate models have been found to be a promising endeavor in multi-objective optimization problems involving expensive analysis and simulation processes such as multi-physics modeling and simulation, finite element analysis (FEA), and computational fluid dynamics (CFD. Developing an optimization algorithm that can easily identify the Pareto frontier of highly nonlinear multi-objective optimization problems with less computation cost is the aim of this work. In this paper, an Adaptive Multi-Objective Optimization approach based Surrogate models (AMOS) is developed to reduce computation cost of fitness evaluations and discover the Pareto optima for multi-objective optimization problems with comparable high accuracy. AMOS explores the design space by sampling using LHD to identify promising regions. Then, AMOS exploits the identified promising region by adaptively constructing the most suitable surrogate model, which could be response surface, radial basis, or Kriging surrogates, in the feasible design space based on root mean square error values (RMSE). AMOS stops iterating when a termination criterion is met, and a Pareto frontier is identified based on developed guidance and fitness functions. AMOS has successfully identified the pareto frontier of practical engineering optimization problems with expensive black box functions and significantly reduced the computation cost. The novel method was put to the test utilizing real-world challenges and engineering design examples such vehicle magnetorheological design and wind turbine airfoil geometry. • Adaptive Surrogate Assisted Multi-Objective Optimization Approach is introduced. • Surrogate approximations were utilized to determine Pareto front of multi-objective problems. • Sample guiding function is applied to guide search and identify Pareto front. • Soft computing tools and algorithms were used to determine optimal design apartments of real life engineering application. [ABSTRACT FROM AUTHOR]

In this paper, by combining the Computational Fluid Dynamics (CFD) and NSGA II algorithm, the forced convective heat transfer ow in a stack of horizontal parallel plates has been multi-objectively optimized. In the optimization process, the distance between the plates in the set of parallel channels has been changed so as to simultaneously optimize the amount of heat transfer between the plates and uid and the pressure drop of the uid (maximization of heat transfer and minimization of pressure drop). The Pareto front, which illustrates the changes of heat transfer from the plates and the pressure drop of uid, simultaneously, has been presented in the results section. This result contains important information regarding the thermal designing of stack of channels subjected to forced convective heat transfer. The Pareto front has been obtained for four different fluids that have different Prandtl (Pr) numbers (mercury, air, water, and oil), and the results related to each uid have been discussed. Finally, the multi-objective optimization results obtained in this paper have been compared with the results of the asymptotic analysis method (which is a single-objective method aimed at increasing the amount of heat transfer from plates) for internal uid ows, and useful information has been obtained. [ABSTRACT FROM AUTHOR]

The present paper focuses on the numerical investigation of the flow around the fully submerged 2D and 3D hydrofoils operating close to a free surface. Iterative boundary element method is implemented to predict the flow field. This study aims to investigate the aspect ratio effect on the free surface interactions and hydrodynamic performance of the hydrofoils under a free surface by using potential flow theory. Three different submergence depths and aspect ratios are studied in the wide range of Froude Numbers. In 3D cases, spanwise width of the numerical wave tank model is selected both equal and wider to the foil span, to observe the sidewall effects. Wave field seems to be two dimensional at low Froude numbers. On the other hand, signs of three dimensionalities are observed on the free surface structure for higher Fn, even the predicted wave elevations are very close to 2D calculations in the midsection. Increment in the Fn give a rise to the amplitude of the generated waves first, however a further increase in Fn has a lowering effect with the beginning of waves spill in the spanwise direction in the form of Kelvin waves. Free surface proximity and resultant wave field are also seeming to be linked with the lift force on the hydrofoil. As aspect ratio of the foil increase, 3D lift values are getting closer to those of 2D calculations. However, it is seen that, 3D BEM predictions of a hydrofoil under free surface effect cannot be considered two-dimensional even the aspect ratio is equal to 8. [ABSTRACT FROM AUTHOR]

In cold regions, traditional air source heat pumps are easily frosted in heating state. The frosting problem can be effectively overcome by the direct-expansion solar/air-assisted heat pump (DX-SASIHP). One of the most critical components in the DX-SASIHP system is the collector/evaporator, whose performance hinges on its structure and material. To improve the heating performance of DX-SASIHP, this paper attempts to optimize the structure and material of the collector/evaporator by the Computational Fluid Dynamics (CFD) method. Specifically, key parameters like tube diameters, rib height, rib thicknesses, and tube material were examined under the same weather conditions. On this basis, the heat collection capacity and heat collection efficiency of the collector/evaporator were evaluated. Finally, the collector/evaporator structure was optimized in the light of heat collection capacity, heat collection efficiency and manufacturing cost. The key parameters were optimized as follows: 23 mm for tube diameter, 45 mm for rib height, 4 mm for rib thickness, and aluminum for tube material. The research results lay a theoretical basis for the collector/evaporator design of DX-SASIHP in heating state. [ABSTRACT FROM AUTHOR]