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Abrasive flow jet machining (ASJM) is modern manufacturing technique which uses comparatively low-pressure abrasive flow jet for machining various machined surfaces like holes, channels and intricate shapes which is not possible from conventional machining processes. The effect of abrasive particle concentration on the impacting slurry velocity on the surface was examined in the present CFD simulation, resulting in target surface erosion. To predict the impact velocity of abrasive particles hitting the surface, a 2D CFD model was used. The depth of machined surface, surface irregularity and surface removal rate at normal incidence mainly depend on the KE of particle, impact angle, etc. in line with previously published research work on highly pressurised air and water driven abrasive jet. In the present work CFD simulation is performed to predict the effect of solid particle concentration on the impacting slurry jet velocity at the target surface and also turbulence kinetic energy near the surface is studied. As per the CFD results the simulation model predictions the velocity of impacting particle goes on decreasing due to internal frictional resistance between solid and liquid phase and it shows scope of further parametric analysis in this area.

This study addresses performances and behaviors of the multi-cross-section HAWT blade design with and without fences. The FX66-S-196 V, FX63-137 S and SG6043, supercritical airfoils were used and distributed along the blade radius; further, the NACA4412 single-cross-section HAWT blade having the same dimensions was used to compare the behaviors and overall performances of all the blades. Analyses were then performed numerically using blade elements momentum BEM theory with a self-code (F.90) and CFD as well as experimentally with three multi-cross-section blades designed using SOLIDWORKS and 3D- printed with polylactic acid. the multi-cross-section HAWT blades show good performance compared with the single- cross-section blade, with an approximately 8% increase in power coefficient, i.e., 40 W, for a miniature wind turbine (127 cm diameter 500 W output power) and greater improvements for wind turbines with large diameters. The fences were designed using boundary layer theory and installed on multi-cross-section blades in experimentally determined positions. The fences showed high performance, with a 16% increase in total power coefficient and high flutter stability.

In this study, based on a closed bomb test combined with computational fluid dynamics, a structural finite element method, and an acoustic boundary element method, a fluid-solid acoustic one-way coupling calculation model is established for the combustion process of energetic materials in a closed bomb, and the effectiveness of the model is verified by experiments. It is found that the maximum peak sound pressure increases exponentially with an increase in loading doses or gas pressure. However, a change in the combustion coefficient of the energetic materials has little effect on the noise generated during the combustion process in the closed bomb. When the combustion coefficient is reduced by a multiple of 16, the maximum transient sound pressure is reduced by 1.79 dB, and the sound pressure level in the frequency band is reduced by 1.75 dB. With an increase in shell thickness, the combustion noise of the energetic materials in the closed bomb decreases, and the reduction range of the combustion noise increases with the increase in shell thickness.

Thermoacoustics is about conversion between thermal and acoustical energies to provide alternative green technology for power cycle and cooling system. The oscillatory flow across porous structure inside the system is playing the role of energy conversion between the acoustic wave and the surface of the porous structure. Better understanding of fluid dynamics of oscillatory flow inside thermoacoustic system is therefore important for the thermoacoustic based energy conversion system. This paper presents the ‘entrance’ and ‘exit’ effects of the oscillatory flow within a parallel-plate structure that is placed inside a standing-wave thermoacoustic environment. Two-dimensional SST k-ω CFD models which were validated using experimental data and theoretical predictions were used for this investigation. Two different operating frequencies of 14.2 Hz and 23.6 Hz were studied for flow with five different amplitudes that were represented using drive ratios of 0.3%, 0.83%, 1.5%, 2.1% and 3%. These correspond to cases with Reynolds numbers between 5936 and 62926. Due to the cyclic nature of the flow, a region defined as an ‘exit’ region was observed in addition to the usual ‘entrance’ region and the fully developed region for flow inside a channel. The change of shape of velocity profiles from the ‘m’ shape profile, to the ‘slug-like’ profile and ‘parabolic-like’ profile was discussed in relation to the ‘entrance’ and ‘exit’ effects on flow inside the channel. The ‘entrance’ and ‘exit’ effects become bigger as drive ratio increases. The effect of ‘entrance’ and ‘exit’ are slightly reducing as frequency increases from 14.2 Hz to 23.6 Hz. This may be related to the shorter travel distance of fluid as the frequency increases. The results shown in this paper suggest that the flow within a 200 mm parallel-plate structure should be treated as developing flow especially for flow with low resonance frequency at drive ratio higher than 1%.

The coaxial mixers enhance the suspension of concentrated slurries in an agitated reactor. In this research work, the complex slurry suspension and dissemination behavior in a coaxial slurry mixing system (comprised of a close clearance anchor rotating with a low speed and an inner axial impeller rotating with a high speed) was analyzed employing ERT (electrical resistance tomography, a non-intrusive flow visualization technique), and computational fluid dynamics (CFD). The numerical models were validated by comparing the axial solid concentration profiles generated using the ERT data and the CFD simulation results. The influences of various important parameters such as the diameter of the inner axial impeller, the inner impeller type, and the inner impeller spacing on the hydrodynamic characteristics of the slurry suspensions in a coaxial mixing vessel were thoroughly analyzed. The radial and axial velocity profiles of solid particles were generated using the validated mathematical models. The assessment of energy loss due to the solid–solid collisions, the particle–fluid frictions, and the particle–vessel wall collisions was conducted. The evaluation of optimum inner impeller clearance and inner impeller diameter is essential to attain a high degree of solids suspension and dissemination in a coaxial slurry mixing system.

Thermal analysis plays an important role in predicting the overall performance of an electric machine. An accurate Heat Transfer Coefficient (HTC) is required for an accurate and reliable thermal model representing the amount of heat that can be transferred by the system. Analytical calculation of HTC is difficult for sophisticated geometric bodies since the correlations are only available for simple geometries. This paper presents a 2- way numerical multi-physics approach using Finite Element Analysis (FEA) and Computational fluid dynamics (CFD) to determine HTC and evaluate the thermal performance of a liquid-cooled electric machine. The approach presents a convenient, time-efficient, and reliable solution applicable to the optimization process. The numerically obtained HTC for a commonly used coolant channel in liquid-cooled electric machines is verified analytically using correlations. The study uses a 60 kW switched reluctance machine (SRM) as an example model to evaluate the thermal performance of the machine. Results are validated with the experimentally obtained data.

A 90° elbow equipped with guide vanes was developed with the intent of reducing elbow erosion. Numerical models were formed to predict the maximum erosion rate of elbow and Face-1, and the response surface methodology was used to study the relationship between the erosion rate and structural parameters of guide vane. A second-order response surface model was established to determine the relationship between R1 and variables, and a reduced cubic (RC) polynomial model was obtained to reveal the relationship between R2 and the three factors. The numerical results show that the low-speed region is expended and the maximum discrete particle matter (DPM) concentration is reduced after installing the guide vane. This internal component provides a shelter for the elbow from the direct impact of high-speed solids.

Ground effect dramatically improves the performance of the Wing-in-Ground (WIG) vehicles near the ground. However, making coordinate turnings in ground effect zone may raise complexity in flight control. The Angle of Attack (AOA) and height are believed to be important factors. To find the impact of these factors, three straight rectangular wings with different aspect ratios are simulated via CFD approach. The results show that in normal situations, the rolling moment tends to level the wing but less effective with the decreasing AOA and changes its direction when the AOA is less than a height dependent value. The yaw moment exhibits complex behavior because two different effects generate oppose moments. The rolling moment coefficient is more influenced by the ground if a wing has larger Aspect Ratio (AR) and works at low to medium AOA. The yawing coefficient is always more influenced if the wing has larger AR regardless AOAs. These findings can provide basic guidance for the design of control system and enable aircraft designers to reshape the crafts to avoid or utilize this effect.

As a key mission of the modern traffic management, crowd flow prediction (CFP) benefits in many tasks of intelligent transportation services. However, most existing techniques focus solely on forecasting entrance and exit flows of metro stations that do not provide enough useful knowledge for traffic management. In practical applications, managers desperately want to solve the problem of getting the potential passenger distributions to help authorities improve transport services, termed as crowd flow distribution (CFD) forecasts. Therefore, to improve the quality of transportation services, we proposed three spatiotemporal models to effectively address the network-wide CFD prediction problem based on the online latent space (OLS) strategy. Our models take into account the various trending patterns and climate influences, as well as the inherent similarities among different stations that are able to predict both CFD and entrance and exit flows precisely. In our online systems, a sequence of CFD snapshots is used as the training data. The latent attribute evolutions of different metro stations can be learned from the previous trend and do the next prediction based on the transition patterns. All the empirical results demonstrate that the three developed models outperform all the other state-of-the-art approaches on three large-scale real-world datasets.

The quest to achieve high launching frequency and higher speed is one of the key goals for researchers in the field of underwater projectiles. Many methods have been proposed for reducing the drag force to reach higher speed, such as superhydrophobic surface, compliant surface, and so on. One of the most effective methods is supercavitating drag reduction technology, which can be used to achieve a significant reduction of hydrodynamic drag by wrapping a large, continuous cavity around the underwater projectile. To increase launching frequency and decrease drag force of underwater projectiles, a serial multi-projectiles structure based on the principle of supercavitation is proposed in this paper. However, the matching relationships of serial multiprojectiles between different conditions (cavitation number, distance between projectiles, etc.) and the drag characteristics have not been investigated, because obtaining the relationship between drag characteristics and different conditions requires simulation time and extensive calculations. In this paper, computational fluid dynamics (CFD) method and machine learning method were coupled to investigate the natural supercavitation phenomenon of the serial projectiles to reduce the computational cost and improve the simulation accuracy. Firstly, the numerical simulation model for the underwater supercavitating projectile is established and verified by experimental data. Then the evolution of the supercavitation for the serial multi-projectiles is described. In addition, the effects of different cavitation numbers and different distances between projectiles are investigated to demonstrate the supercavitation and drag reduction performance. Finally, the artificial neural network (ANN) model is established to predict the evolution of drag coefficient based on the data obtained by CFD. The results predicted by ANN are in good agreement with the data obtained by CFD. The findings provide helpful guidance for the research on the drag reduction characteristics of underwater serial projectiles. The main conclusions of the study are as follows: (1) The cavity will develop, fuse and collapse in the water and natural supercavitation phenomenon is observed when underwater serial projectiles move at a high speed. The serial multi-projectile structure can reduce the drag of the second projectile and achieve the goal of drag reduction. (2) The length and aspect ratio of supercavity around serial projectiles decrease with the decreasing of the cavitation number, and the drag coefficient of the second projectile decreases. The length and aspect ratio of supercavity decrease with the 3 decreasing of the distance between serial projectiles, and the drag coefficient of the second projectile decreases. (3) The drag coefficient of the second projectile predicted from the ANN model has a high accuracy, where the regression R2 values of training, validation, and testing samples are above 0.99. Machine learning has an obvious advantage in simplifying computational complexity and increasing computational efficiency. Furthermore, the discussion of different cases is based on static projectiles. However, in real-world applications, the movement of serial projectiles should be considered. This is the future direction for this work.

Hypersonic high-enthalpy wind tunnels have been a challenge to ground tests in aerospace research area for decades and its test flow uniformity is one of the most important parameters for evaluating wind tunnel performances. Regarding to the performance requirement, theories and methods for designing hypersonic flow nozzles at high enthalpy conditions are quite difficult, but very interesting topics, especially when air molecule dissociations take place in wind tunnel test gas reservoirs. In this paper, fundamental theories and important methods for nozzle designs are briefly reviewed with the emphasis on two-dimensional axisymmetric nozzles for hypersonic high-enthalpy wind tunnels, including the Method of Characteristics (MOC), the graphic design method, the Sivells method, the theory for boundary correction, and the CFD-based design optimization methods. These theories and methods had been proposed based on several physical issues, respectively, which play important roles in nozzle flow expansion processes. These issues cover the expansion wave generation and reflection, the boundary layer development, the real gas effect of hypersonic high-enthalpy flows. Difficulties arising from applications of these methods in hypersonic high-enthalpy nozzle design are discussed in detail and the state of the art of the nozzle design technologies that have reached for decades is summarized with some brief comments. Finally, the prospect for the hypersonic nozzle design methods, and its numerical and experimental verifications are provided with from authors’ viewpoint for readers’ reference.

The ability of flying continuously over prolonged periods of time has become target of numerous research studies performed in recent years in both the fields of civil aviation and unmanned drones. High-altitude platform stations are aircrafts that can operate for an extended period of time at altitudes 17 km above sea level and higher. The aim of this paper is to design and optimize a wing for such platforms and computationally investigate its aerodynamic performance. For that purpose, two-objective genetic algorithm, class shape transformation and panel method were combined and used to define different airfoils with the highest lift-to-drag ratio and maximal lift coefficient. Once the most suitable airfoil was chosen, polyhedral half-wing was modeled and its aerodynamic performances were estimated using the computational fluid dynamics approach. Flow simulations of transitional flow at various angles-of-attack were realized in ANSYS FLUENT and various quantitative and qualitative results are presented, such as aerodynamic coefficient curves and flow visualizations. In the end, daily mission of the aircraft is simulated and its energy requirement is estimated. In order to be able to cruise above Serbia in July, an aircraft weighing 150 kg must accumulate 17 kWh of solar energy per day.

Iosif Taposu has formulated a mathematical model and generated a family of airfoils whose geometry resembles the dolphin shape. These airfoils are characterized by a sharp leading edge and experiments have proven that they can achieve better aerodynamic characteristics at very high angles of attack than certain classical airfoils, with the nose geometry inclined downwards. On the other hand, they have not been applied to any commercial general aviation aircraft. The authors of this paper have been motivated to compare the aerodynamic characteristics of widely used NACA 2415 airfoil with Taposu’s dolphin that would have the same principal geometric characteristics. A CFD calculation model has been established and applied on NACA 2415. The results were compared with NACA experiments and very good agreements have been achieved in the major domains of lift and polar curves. The same CFD model has been applied on the counterpart Dolphin 2415. Results have shown that the Dolphin has a slightly higher lift/drag ratio in the lift coefficient domain 0.1 ÷ 0.35 than NACA. On the other hand, at higher and lower lift coefficients, its aerodynamic characteristics were drastically below those of the NACA section, due to the unfavorable influence of the Dolphin’s sharp nose. A series of the Dolphin’s leading edge modifications has been investigated, gradually improving its aerodynamics. Finally, version M4, consisting of about 70% of Dolphin’s original rear domain and 30% of the new nose shape, managed to exceed the NACA’s characteristics, thus paving the way to investigate the Dolphin hybrids that could be suitable for the general aviation industry.

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.

Non-uniform sand retention behavior often occurs to the serviced screen deteriorating erosion. However, this phenomenon is poorly understood. This paper presents a numerical study of the sand retention on wire-wrapped screens, with special reference to non-uniform behaviors. This is done by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM). The validity of the model has been validated for dry and wet sand screen systems. It is used here to study sand retention behaviors at different solid concentrations and particle size distributions (PSD). Via this model, five distinct sand retention modes are identified: No sand retention (Mode I), partial sand retention (Mode II), sand retention with slow sequential bridging (Mode III), sand retention with fast sequential bridging (Model IV) and sand retention with instantaneous bridging (Mode V). Modes II and III belong to non-uniform sand retention, which develops strong local flows that induce local erosion or hot spot on the screen. A phase diagram is introduced to predict these five modes and their transition with respect to solid concentration and PSD. Additionally, the predicted flow and force structures are analyzed in detail. The results indicate that the bridging over a slot heavily relies on the particle accumulation on the screen. A new screen with a converging slot configuration is proposed to improve this particle accumulation. This improvement helps develop uniform sand retention on the screen.

The Shell-and-tube type heat exchangers have long been widely used in many fields of industry. These types of heat exchangers are generally easy to design, manufacturing and maintenance, but require relatively large spaces to install. Therefore the optimization of such heat exchangers from thermal and economical points of view is of particular interest. In this article, an optimization procedure based on the minimum total cost (initial investment plus operational costs) has been applied. Then the flow analysis of the optimized heat exchanger has been carried out to reveal possible flow field and temperature distribution inside the equipment using computational fluid dynamics. The experimental results were compared with computational fluid dynamics analyses results. It has been concluded that the baffles play an important role in the development of the shell side flow field. This prompted us to investigate new baffle geometries without compromising from the overall thermal performance. It has been found that the heat exchanger with the new baffle design gives rise to considerably lower pressure drops in the shell side, which in turn reducing operating cost. The new baffle design is particularly well suited for shell-and-tube heat exchangers, where a viscous fluid flows through shell side with/out phase change.

Deep learning has been probed for the airfoil performance prediction in recent years. Compared with the expensive CFD simulations and wind tunnel experiments, deep learning models can be leveraged to somewhat mitigate such expenses with proper means. Nevertheless, effective training of the data-driven models in deep learning severely hinges on the data in diversity and quantity. In this paper, we present a novel data augmented Generative Adversarial Network (GAN), daGAN, for rapid and accurate flow filed prediction, allowing the adaption to the task with sparse data. The presented approach consists of two modules, pre-training module and fine-tuning module. The pre-training module utilizes a conditional GAN (cGAN) to preliminarily estimate the distribution of the training data. In the fine-tuning module, we propose a novel adversarial architecture with two generators one of which fulfils a promising data augmentation operation, so that the complement data is adequately incorporated to boost the generalization of the model. We use numerical simulation data to verify the generalization of daGAN on airfoils and flow conditions with sparse training data. The results show that daGAN is a promising tool for rapid and accurate evaluation of detailed flow field without the requirement for big training data.

This paper aims to systematically investigate the cataracting-centrifuging transition in a rotary drum involving spherical and nonspherical particles by using the Multiphase Granular Eulerian Model (MGEM). The effects of drum length and particle shape on the cataracting-centrifuging transition behavior were analyzed. The results showed that drum length plays an important role in the cataracting-centrifuging transition, although most related works in the literature do not consider this. The particle shape also significantly affects the cataracting-centrifuging transition behavior. Nonspherical particles required lower rotation speeds than spherical particles to reach the centrifuging condition. The particle shape was shown to be related to the critical solid fraction (αsc) from Schaeffer’s model, although further investigations are required to completely correlate particle spherecity with critical solid volume fractions.

In the present numerical examination, thermal characteristics of a rectangular and elliptical fin are compared. The problem considered is assessed with convective tip in a realistic manner. The basic conservation equations are solved by employing SIMPLE scheme in FLUENT 15.0. The numerical results shown 5% enhancement in heat transfer rate through elliptical fin than that of rectangular fin. Also, the attained numerical results are compared with the analytical values and are found to be in good accordance. Moreover, this study forms a basic paradigm for young researchers to understand the importance of CFD in the field of IC engines.

A Francis hydro turbine can be used in large as well as small hydro power plant. Due to complex flow phenomenon in turbine, deriving a hydrodynamic behaviour of flow through experimentation is a tedious job. These phenomena such as flow separation around turbine blade, pressure drop in runner and draft tube, etc. can be captured through a numerical study. A numerical approach needs turbulence modelling to capture fluctuating component of flow variables. In view of that, a comprehensive study has been carried out to find the sensitiveness of various turbulence modelling on the stability of numerical solution. In present study, three different turbulence models such as Standard k - e , Standard k - ω and SST model have been considered. To carried out this study, three different loading conditions have been chosen i.e. part-load, BEP and over-load condition. This study has been carried out by using ANSYS CFX (18.1) CFD solver. It has been observed that at part-load condition, Standard k - e model performed better as compared to other model but at other loading conditions SST model delivered accurate results. Also, turbulent nature of flow at the outlet of runner is well captured by SST model.

In this paper, the primary emphasis was on the modelling and study of aircraft winglets. Drag mitigation is a major problem in aerodynamic engineering. A gadget called a winglet is mounted vertically at a series of angles on the end of the aircraft wing to minimise drag. By decreasing the aircraft drag, the winglet configuration would decrease the fuel consumption and making the aircraft more stable during takeoff, as well as giving the aircraft engine a longer life by reducing the load on the engine thrust. The aim is to design and simulate a using CATIA V5, which is used to build the various winglet models (blended winglet, rated winglet) at different winglet angles (350, 650 and 900) with angle of attack and ANSYS is used to measure and simulate the winglet model. In this study it was observed that wings with winglets produce higher lift force/Drag for the CFD and its static FE analysis study. Its effectiveness is reduced by a certain degree of angle of attack and by rising further to a higher angle of attack. A potential solution for enhancing the aerodynamic performance of an aircraft seems to be the examined idea of variable angle winglets.

Fluid flows hosting electrical phenomena make the subject of a fascinating and highly interdisciplinary scientific field. In recent years, the extraordinary success of electrospinning and solution blowing technologies for the generation of polymer nanofibers has motivated vibrant research aiming at rationalizing the behavior of viscoelastic jets under applied electric fields or other stretching fields including gas streams. Theoretical models unveiled many original aspects in the underpinning physics of polymer solutions in jets, and provided useful information to improve experimental platforms. This article reviews advances in the theoretical description and numerical simulation of polymer solution jets in electrospinning and solution blowing. Instability phenomena of electrical and hydrodynamic origin are highlighted, which play a crucial role in the relevant flow physics. Specifications leading to accurate and computationally viable models are formulated. Electrohydrodynamic modeling, theories for the jet bending instability, recent advances in Lagrangian approaches to describe the jet flow, including strategies for dynamic refinement of simulations, and effects of strong elongational flow on polymer networks are reviewed. Finally, the current challenges and future perspectives of the field are outlined and discussed, including the task of correlating the physics of the jet flows with the properties of realized materials, as well as the development of multiscale techniques for modelling viscoelastic jets., Comment: 135 pages, 42 figures

Two-body point absorbers are useful for wave energy conversion in high energetic and high wave period sea locations. Analysis and simulation show that the two-body point absorbers have high efficiencies which makes them a potential candidate to promote wave energy harvesting technology towards commercialization and implementation. The submerged body of the two-body point absorbers has a large effect on their performance, hence the question arises: which geometric shape of the submerged body will lead to the best performance of the two-body wave energy harvesters? This paper presents a comprehensive study that analyses the different shapes of the submerged bodies based on the numerical wave tank simulated viscous drag coefficient and hydrodynamic property parameters of the oscillating device. A set of transient and three-dimensional computational fluid dynamic simulations of a numerical wave tank were carried out in Ansys Fluent to determine the viscous drag coefficients of the different submerged body shapes. And then the boundary element hydrodynamic simulation and linear dynamic frequency-domain modeling have been applied to identify the optimized PTO damping. Finally, non-linear time-domain modeling has been applied with the identified viscous damping drag coefficient and PTO damping coefficients to predict and compare the power output performance of different large-scale devices with different shapes of submerged bodies. It is found that each submerged body shape is suitable for a different range of wave frequencies, as one must establish a balance between the hydrodynamic properties and the viscous drag of the submerged body based on the sea location. It is also found that the typical viscous drag coefficient values used in the past studies underestimate the drag coefficient, and the linearized model widely adopted in frequency domain models is non-accurate for the devices with large viscous drag forces.

To study the internal flow characteristics of the photovoltaic pump under the transient change of solar radiation, the simulation algorithm of the photovoltaic pump system was established by MATLAB/Simulink and CFD for the first time and the results were validated by the test. Firstly, the change rule of pump flow rate and rotation speed under transient solar radiation was obtained by Simulink. Then the results of the change rule were transformed into the boundary condition of CFD by CEL function and the transient flow field in the photovoltaic pump was obtained. The internal flow characteristics and pressure pulsation in the pump were analyzed when the solar radiation increases or decreases transiently. The results demonstrate that the numerical calculation can provide accurate prediction for the characteristics of internal flow in the pump. The numerical results are closed to the experimental results, the minimum error of pressure is 0.93% and the maximum error is 1.78%. When the solar radiation increases transiently, the low pressure area at the impeller inlet gets larger obviously and the jet-wake at the impeller outlet becomes more obvious. The pressure pulsation in the impeller gradually increases and becomes stable after 0.6 s. The pressure from the impeller outlet to the guide vane outlet is stable at 123 kPa. When the solar radiation decreases transiently, the pressure in the impeller takes 1.6 s to be stable. Larger pressure pulsation occurs from the impeller outlet to the guide vane inlet and the maximum differential pressure is 10 kPa. Compared with the transient increase of solar radiation, the pressure in the impeller takes over 0.2 s to stabilize when the solar radiation transient decreases. Meanwhile, the results in this paper can provide references for other transient characteristics research. Highlight First, the relation between pump flow rate and rotation speed under transient solar radiation was obtained by Simulink. Then the results from Simulink were transformed to be the boundary condition of CFD by CEL function. The internal flow characteristics and pressure pulsation in the pump were analyzed under the instantaneous increase or decrease of the solar radiation.

Environmental flows are generally characterized by complex bed morphology and high current speeds. Such configurations favor the formation of vortex structures that strongly affect hydrody-namics and sediment transport. Large-Eddy Simulation (LES) enables investigation of the dynam-ics of the largest turbulence scales and, thanks to enhanced calculation resources, has now become applicable for simulating environmental flows. In this paper, a LES approach is developed in a CFD code (TELEMAC-3D), which was originally developed to simulate free surface flows using RANS methods. The present developments involve implementing subgrid models, boundary con-ditions and numerical schemes suitable for LES. The LES version of TELEMAC-3D was validated by comparing results on the model with experimental data for flow past a cylinder. Then, the model was applied to a test case representing flow over dunes. After validating the hydrodynamics, the model was used to assess the bottom shear stress, using both a RANS and a LES approach. Com-parison highlighted the potential contribution of LES to investigating the hydrodynamic forces acting on the bottom.

Particulate flows in a mixture of gas and liquid, i.e. gas–liquid–solid three-phase flows, are frequently encountered both in nature and industry. In such flows, complex interactions between multiple phases, i.e. particle–particle interactions, fluid–particle interactions and interfacial interactions (such as surface tension and particle wetting), play a crucial role. In literature, simulations of three-phase flows are sometimes performed by incorporating interface capturing methods (e.g. VOF method) into the CFD–DEM coupling model. However, it is practically impossible to perform large (industrial) scale simulation because of the high computational cost. One of the strategies often employed to reduce the computational cost in CFD–DEM is to upscale particle size, which is applied mainly to particle single-phase and fluid–solid two-phase flows. The present work is focused on the scaled-up particle model for gas–liquid–solid three-phase flows. The interaction forces between multiple phases are scaled using the general criteria derived from the continuum assumption of particulate flow. A colour function based interface-capturing method with improved interface smoothness is developed, and the diffusion based coarse graining is employed to ensure sufficient space resolution in CFD even when particle size is increased. It is shown that the model developed is capable of predicting the both particles and fluid behaviour in the original system.

When the number of wind farms increases, the number of wind turbines placed in forested areas will also increase, this is because of the large forest areas in Sweden. When the wind turbines are placed in forested areas the fatigue loads increase drastically, so their maintenance costs increase making them less profitable. In this work clearings in forest are studied to be able to increase the electrical power generated by the wind turbines and decrease the fatigue loads to make them more profitable. The approach in this work is to use Computational Fluid Dynamics (CFD) with the Large Eddy Simulation (LES) turbulence model coupled to an aero elastic solver that solves the dynamic response of the wind turbine. Here Ryningsnas in Sweden is investigated with a homogeneous forest, the current clearing and an extended clearing. The electrical generator power was highest for the current clearing. But the fatigue loads were both higher and lower than the homogeneous forest depending on which part of the wind turbine that was investigated. The extended clearing nearly always had the lowest fatigue loads but unfortunately also the lowest electrical generator power. Further optimization of the clearings and the wind turbine locations in relation to them is needed to find the sweet spot where the fatigue loads are lower and the electrical generator power is higher.

Dust emissions during storage of non-moving bulk materials are studied with a numerical method. The model relies on a contact-model-free Discrete Element Method (DEM) to model the bulk particle–fluid interaction and the dust removal coupled with Computational Fluid Dynamics (CFD) to model the gas and the dust phase in a multiphase framework. Here, two storage scenarios are considered: a flown through packed bed and a flown over stockpile. For the first, the performed simulations reveal that the dust discharge can be correlated with the passing fluid pressure drop. For the second, a parameter study of factors influencing the dust emissions is performed. The parameters discussed are the stockpile size, the gas velocity, the slope angle, the particle diameter and the shape of the stockpile, taking into account conical and truncated conical stockpiles. Dust release correlations are obtained for both scenarios, which reflect very well the obtained numerical results.

First, the Authors are to be congratulated on their paper, in which the depressurization process in a drainage system has been analysed experimentally and numerically. The drainage system contains ...

Biofouling represents an important problem in the shipping industry since it causes the increase in surface roughness. The most of ships in the current world fleet do not have good coating condition which represents an important problem due to strict rules regarding ship energy efficiency. Therefore, the importance of the control and management of the hull and propeller fouling is highlighted by the International Maritime Organization and the maintenance schedule optimization became valuable energy saving measure. For adequate implementation of this measure, the accurate prediction of the effects of biofouling on the hydrodynamic characteristics is required. Although computational fluid dynamics approach, based on the modified wall function approach, has imposed itself as one of the most promising tools for this prediction, it requires significant computational time. However, during the maintenance schedule optimization, it is important to rapidly predict the effect of biofouling on the ship hydrodynamic performance. In this paper, the effect of biofilm on the ship hydrodynamic performance is studied using the proposed performance prediction method for three merchant ships. The applicability of this method in the assessment of the effect of biofilm on the ship hydrodynamic performance is demonstrated by comparison of the obtained results using the proposed performance prediction method and computational fluid dynamics approach. The comparison has shown that the highest relative deviation is lower than 4.2% for all propulsion characteristics, lower than 1.5% for propeller rotation rate and lower than 5.2% for delivered power. Thus, a practical tool for the estimation of the effect of biofouling with lower fouling severity on the ship hydrodynamic performance is developed.

In order to solve the problems of non-uniform gas concentration distribution and serious flooding in the parallel flow field of traditional PEMFC, a stepped flow field of PEMFC bipolar plate is proposed in this paper. The gas concentration distribution, velocity distribution, liquid water distribution and current density distribution of traditional parallel flow field and stepped flow fields are studied by computational fluid dynamics (CFD) simulations. The results suggest that the fuel cells with stepped flow field are superior than the traditional fuel cell with parallel flow field. Compared with fuel cell with parallel flow field, the net power of fuel cell with stepped flow field is increased by 21.5%. Moreover, the stepped flow fields can improve the uniformity of gas concentration and current density distribution, accelerate the discharge of liquid water, alleviate water flooding phenomenon.

The broadband noise can be dominant or important for total characteristics for marine propeller noise representing the minimum base of self-noise. Accurate prediction of such noise is crucial for survivability of underwater military vessels. While the FW-H Formulation 1B can be used to predict broadband trailing edge noise, the method required experiment measurements of surface pressure correlations, showing its limitations in generality. Therefore, in this study, the methods are developed to utilize wall pressure spectrum models to overcome those limitations. Chase model is adopted to represent surface pressure along with the developed formulations to reproduce pressure statistics. Newly developed method is validated with the experiments of airfoils at different velocities. Thereafter, with its feasibility and generality, the procedure incorporating computational fluid dynamics is established and performed for a propeller behind submarine hull. The results are compared with the experiments conducted at Large Cavitation Tunnel, thus showing its usability and robustness.

In the field of civil engineering, the meteorological data available usually do not have the detailed information of the wind near a certain site. However, the detailed information of the wind field during typhoon is important for the wind-resistant design of civil structures. Furthermore, the resolution of the meteorological data available by the civil engineers is too coarse to be applicable. Therefore it is meaningful to obtain the detailed information of the wind fields based on the meteorological data provided by the meteorological department. Therefore, in the present study, a one-way coupling method between WRF and CFD is adopted and a method to keep the mass conservation during the simulation in CFD is proposed. It is found that using the proposed one-way coupling method, the predicted wind speed is closer to the measurement. And the curvature of the wind streamline during typhoon is successfully reproduced.

Tidal stream turbines (TST) deployed in open-water energetic sites are often unintentionally at yaw to the incoming flow that causes performance degradation and deflection of the wake. Wake steering is a popular concept in wind arrays where the upstream turbine is operated intentionally at yaw to steer the wake away from a downstream turbine. To explore such arrangements for TST arrays, a synergistic experimental and numerical campaign was undertaken to characterize a TST performance and wake deflection subjected to ±15° yawed inflow. The near-wake characterization study was performed using complementary acoustic Doppler velocimetry measurements and 3D computational fluid dynamics. The experiments show a ∼10% reduction in the maximum power coefficient. In the near field, the deflected wake morphed into an elliptical shape due to the formation of two counter-rotating vortices. The wake deflection results in enhanced momentum transfer and dissipation, leading to accelerated energy recovery. When the upstream turbine is yawed, available kinetic energy in the flow for the downstream turbine is at least 50% higher with the turbine array in a staggered configuration compared to the inline configuration. Our results provide guidance in reducing the cross-stream and downstream spacing between turbine units in an array.

The crossflow is the key phenomenon in turbulent flow inside rod bundles. In order to establish confidence on application of computational fluid dynamics (CFD) to simulate the crossflow in rod bundles, three Reynolds-Averaged Navier Stokes (RANS) models i.e. the realizable k-e model, the k-ω SST model and the Reynolds stress model (RSM), and the Large Eddy simulations (LES) with the Wall-Adapting Local Eddy-viscosity (WALE) model are validated based on the Particle Image Velocimetry (PIV) flow measurement experiment in a 5 × 5 rod bundle. In order to investigate effects of periodic boundary condition in the gap, the numerical results obtained with four inner subchannels are compared with that obtained with the whole 5 × 5 rod bundle. The results show that periodic boundaries in the gaps produce strong errors far downstream of the spacer grid, and therefore the full 5 × 5 rod bundle should be simulated. Furthermore, it can be concluded, that the realizable k-e model can only provide reasonable results very close to the spacer grid, while the other investigated models are in good agreement with the experimental data in the whole downstream flow in the rod bundle. The LES approach shows superiority to the RANS models.

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.

The small time-step due to the small size of microcapsules using the discrete element method (DEM) requires a significant number of computations when analyzing the force condition of microcapsules for mixing self-healing concrete. In this study, a speed-up method with a reduced Young's modulus is proposed to correct the particle contact force after establishing the relationship between the maximum contact force and the Young's modulus of particles in the collision process by using theoretical derivations and data fitting. The proposed method was verified using a stirred box model with the DEM and a stirred tank model with computational fluid dynamics–DEM. The effects of different particle numbers, impeller speeds, and time-step sizes on the accuracy of the proposed method were investigated. The results demonstrated the feasibility of analyzing the maximum contact force between particles using the speed-up method with a reduced Young's modulus.

This work proposes and employs a mixed-complexity modeling approach to creating a 3D computational fluid dynamics (CFD) model to predict the syngas production from Miscanthus briquettes in a two-stage downdraft gasifier operating with different gasification fluids. The study was performed at steady state regime in the Ansys Fluent environment considering the non-premixed combustion model. A probability density function is also included as a tool for the description of the chemical kinetics to predict the syngas composition following the main chemical reactions involved in the gasification process. The goal of this approach is to reduce the computational cost while still providing accurate predictions. In comparison to experimental gasification with air, the model correctly predicts the temperature profile inside the reactor, the composition of the syngas (CO, H2 and CH4), and therefore the lower heating value (LHV). For cases involving the use of saturated steam and oxygen as gasification fluids, the model predicted key species concentrations in the gasification zone and the reactor core and accurately described the significant increase in the LHV of the syngas. This approach opens the possibility of studying the gasification process in moving-bed reactors using different gasification fluids and feedstocks based on their elemental and proximate analysis.

Bends are potentially most problematic in a hydraulic conveying pipeline system. This paper presents a numerical study of hydraulic bends, with special reference to the interaction between pipe orientation and flow regime. This is done by the combined approach of computational fluid dynamics and discrete element method facilitated with a wear model. The validity of the model has been verified by comparing the measured and predicted flow properties and erosion depth. On this basis, three pipe orientations: 0° (i.e. horizontal-vertical bend), 45° (i.e. inclined bend), and 90° (i.e. vertical-horizontal bend) are simulated for the conveying speeds of 1.2 m/s, 2.0 m/s and 4.0 m/s. It covers typical flow regimes in a horizontal pipe. Via the simulation outputs, the bend performance is assessed in terms of pressure loss, conveying instability and bend erosion. The results reveal that the pressure drop and erosion rate differ for various pipe orientations and conveying speeds involving different flow regimes. The acceleration/de-acceleration of the particles exiting the bend does not result in a significant additional pressure. The vertical-horizontal bend has low erosion rates benefiting from cluster formation and low pressure, which is not the case at high conveying speeds. By contrast, the inclined bend gives the highest elevation height and does not suffer significant pressure drop, pressure fluctuation, and erosion rate under all the flow regimes considered.

Renewable energy has become very prominent these days because of its sustainable and environment-friendly nature. The soil heat storage system plays an important role in the long-term storage of solar energy to ensure a consistent power supply. The experimental analysis and practical implementation of soil heat storage system are very difficult due to its large size and the simulation-based calculation is also very complex for the entire storage system. In order to reduce the system from the perspective of space and time, this paper has applied a similar function relationship for soil heat storage system and develops the traditional CFD simulation model and similar model. According to the dimensions of similar model, the corresponding experimental setup is constructed and the experimental results of long-term heat storage in the soil are compared with the calculation results of a CFD similar model. The relative error of inlet and outlet temperature difference is measured 10% and the error for soil temperature rise is below 1 °C. The proposed method has reduced the simulation and experimental workload for soil heat storage using similarity theory. Hence, the proposed method has great significance in the research domain of soil heat storage and the application of similarity theory.

Unsteady flow structures unrelated to rotating frequency in the turbine wheel space cavity has been observed and reported in a number of recent rim sealing investigations. These flow structures are relatively large in scale and have a significant influence on the sealing effectiveness prediction. As a result, it is important to capture these flow structures in numerical simulation. Small computation sectors, due to the circumferential symmetry assumption, have been proved to fail to capture these flow structures. This paper aims to find a minimum computation sector size that can capture these flow structures, at the same time save computation resources and shorten the convergence process for a simple axial rim seal. Four different sector model (10, 20, 30, 180-degree) are set into simulation using RANS and URANS method. The steady and unsteady simulation results are compared. By comparison, the 20-degree sector model is considered appropriate to conduct successive investigations. Then the 20-degree model is set into unsteady simulation under four different sealing flow rates c w = 0 (non-sealing flow case), c w = 2500 , c w = 5000 , c w = 10000 ). It was found that due to the large-scale flow structure, a staggering pressure distribution is found in the cavity. Increasing the sealing flow rate diminishes these structures and stabilizes the flow in the wheel space cavity. The staggering pressure distribution causes the sealing effectiveness to show an abnormal variation trend. Unsteady pressure oscillation waves at two different circumferential positions are subjected to cross-correlation analysis, by which the rotating speed and number of the flow structure could be calculated.

Rotating holes are widely used in jet engine internal air systems as an important kind of throttling element. The flow characteristics of rotating holes are of great importance in the design of the internal air system. This paper aims to investigate the influence of pumping effect on the flow characteristics of axial rotating holes. Pumping effect refers to the flow phenomenon induced by a rotating plate which characterized by a radial outflow. There are altogether two types of holes considered in the paper: round hole and square hole. A 1/25 (14.4-degree) sector model is used to carry out the numerical investigation using the commercial software ANSYS CFX. In the simulation, the SST turbulent model is used. Meanwhile, a non-rotating method using the relative frame of reference is used. In the non-rotating method, an initial incidence angle is given at the inlet instead of setting the plate to be rotating, thus the pumping effect induced by the rotating plate can be eliminated. The non-rotating method results are compared with the conventional reference frame results to investigate the influence of pumping effect. The results show that due to the influence of the pumping effect-induced radial outflow, the theoretical two-dimensional incidence angle becomes three-dimensional, which has negative effects on the hole discharge coefficient. At the same time, due to a larger circumferential length, square holes will undermine the pumping effect, thus has a higher discharge coefficient than the round holes.

The flow and tracer transport in an ozone contactor is simulated by using computational fluid dynamics. The standard k- model, RNG k- model, realizable k- model and SST k- model are used to describe turbulence. A step change method is used to simulate the residence time distribution. The residence time and cumulative residence time are compared with laboratory experiments. All turbulence models can capture the feature of the residence time distribution and cumulative residence time distribution. The residence time distribution in the initial period is sensitive to the used turbulence model, which can affect the value of Morrill dispersion index. The standard k- model behaves better among four turbulence models. HIGHLIGHTS RTD in the initial period is sensitive to turbulence models.; MDI is greatly affected by turbulence models.; The standard k-ɛ model behaves better among four turbulence models.

The most important point in electricity generation with thermoelectric generators (TEG) is to create a temperature difference between its surfaces. The cooling process is usually carried out by liq...

Even though the Wurster technology is commonly used in the pharmaceutical industry for applying coating to beads, additional research work is still necessary to fully understand and control the process. Various simulation approaches have been used extensively in the recent years to investigate different fluidized beds, with and without spray application. The Computational Fluid Dynamics- Discrete Element Method (CFD-DEM) coupled approach is especially suitable to simulate the coating process because it resolves both the fluid and granular flow, and provides detailed particle-scale information. This paper primarily highlights the ability of the CFD-DEM coupled code to capture the thermodynamics and water mass loading of the gas phase in the Wurster coating application by directly comparing the experimental results with the CFD-DEM simulation results, for four different experimental runs and unscaled particle size. It also reports on the four specially designed experiments, giving the measurements of the air temperature and humidity at four points in the coater. The code is verified as well, using a simple simulation test case, with the objective of ensuring the energy and mass conservation in the CFD-DEM communication protocol. The paper also presents the time-averaged contour plots of temperature, humidity and particle volume fraction distribution for four different experiment/simulation cases and provides insights into their spatial distribution in the Wurster coater.

Trough reflectors can produce a reflected solar flux density that is highly concentrated in specific regions of the receiver surface causing higher thermal losses as well as increasing the likelihood of mechanical damage to the receiver. Time-dependent three-dimensional computational fluid dynamics models were developed and used to compare optical and thermal performances of unglazed tubular, evacuated tubular, and open-aperture evacuated receivers for air heating applications. An evacuated partial-annulus receiver with a non-evacuated open-aperture in the high-density solar flux area produced a more uniform concentrated solar flux distribution. With an open aperture to high-density solar flux, an open-aperture evacuated receiver (i) avoids a dense distribution of reflected solar flux in a specific area of an absorber surface thereby contributing to realizing long-term mechanical integrity, (ii) gives a greater optical performance in all types of trough reflector than an evacuated tubular receiver, (iii) tolerates optical mispositioning and (iv) is particularly suited for use with circular trough reflectors.

This study deals with the influence of a rotating cylinder inside the square cavity and multiwalled carbon nanotube–iron oxide (Fe3O4) hybrid nanofluid with water. A two-dimensional system of parti...

In this work, we aim to propose a mathematical formalism for the human liver involving Caputo fractional derivative (CFD) with modified parameters. Regarding the proposed fractional order model (FOM), the positivity and boundedness theory of an explicit solution are established by using the fractional mean-value theorem in the sense of Caputo. In addition, the validation of the FOM is provided to ensure that it complies with the medical interpretation and we also discuss the stability of unique equilibrium point (EP) for the presented model. We apply the Generalized Mittag–Leffler function method (GMLFM) and Predictor–Corrector method (PCM) to solve this model. The GMLFM is used to give the proper results as a series of the time variable to obtain the desired solution at any time and the PCM is implemented to obtain the solution of the FOM over a long time period. The tabled results from this study are compared with the real clinical data and with other methods. The simulations approximate the real clinical data and support the obtained theoretical results. Precisely, the outcomes of the FOM by using the proposed methods coincide with most of the clinical data that means it more accurate. Ultimately, the graphical results indicate the superiority of the proposed FOM over the classical model.