Development Of Computational Fluid Dynamics Research Articles

Large‐scale homo‐ and heterogeneous parallel paradigm design based on CFD application PHengLEI

SummaryThe development of computational fluid dynamics (CFD) highly depends on high‐performance computers. Computer hardware has evolved rapidly, yet scalable CFD parallel software remains scarce. In this article, we design a highly scalable CFD parallel paradigm for both homogeneous and heterogeneous supercomputers. The paradigm achieves the separation of communication and computation and automatically adapts to various solvers and hardware environments, thus reducing programming difficulties and increasing automatic parallelization. Meanwhile, the number of communications is greatly reduced and the scalability of the program is improved through implementing centralized communication and two‐level partitioning techniques. Complex flow problems for real aircraft were then computed on different hardware platforms with a grid size of ten billion. The homogeneous computer hardware includes Intel Xeon Gold 6258R and Phytium 2000+ processors, and the heterogeneous computer platforms include NVIDIA Tesla V100 and SW26010 processors. High parallel efficiency was obtained on all computer platforms, verifying that the paradigm has good automatic parallelization, scalability, and stability. The paradigm in this article has an important reference value for CFD massively parallel computing and can promote the development and application of CFD technology.

Systematic computational methods of unsteady flow simulation based on computational fluid dynamics

Unsteady flow is the dominant flow state in real life; thus, the simulation of it is of vital importance, especially in engineering, for example, the flutter or buffeting of the aerofoil. In the past decades, the progress in computational science greatly paced the development of computational fluid dynamics (CFD), providing powerful tools for simulating unsteady flow via numerical methods. However, the unsteady flow state depends on more variables than a steady flow, including the external conditions in different time moments and the flow's properties that vary with time. The calculation is still too massive, even using CFD. Therefore, CFD algorithms with higher efficiency and less reduction in accuracy are still needed to optimize the technique. This paper reviews the main CFD computational methods that have been maturely developed and proven effective, including direct numerical simulation (DNS), classic turbulence models and reduced order model (ROM), illustrating the main mechanisms and displaying their features. The paper also sheds light on these methods' latest research progress.

Spatial–temporal analysis of magnetohydrodynamics flow and energy flux of power-law nanofluid in a confined domain

Energy flux analysis of power-law fluid is a novel contribution to recent developments in computational fluid dynamics. The study of the unsteady two-dimensional flow with double diffusive effect inside a complex enclosure exhibits great potential in optimizing the heat transfer rate due to the wavy nature of the side walls. The enclosure is confined with the flow circulation due to the thermal and solutal gradients acting along the left and right wavy walls. The computational time and accuracy in results are estimated and compared by implementing the finite volume method and element-free Galerkin technique. The results are obtained in terms of streamlines, isotherms, isoconcentrations, average Nusselt number, Sherwood number, and total entropy generation due to the effect of conventional parameters, namely, power-law index, Rayleigh number, buoyancy ratio parameter, thermophoresis parameter, Brownian motion parameter, and Lewis number with a fixed Prandtl number throughout the computation. The optimized double-diffusive natural convection analysis is based on entropy generation and a calculated Bejan number. The novelty of this paper lies in the implementation of a mesh-free approach, which may be useful for the further analysis of elliptical/semi-elliptical structures.

Applications of Advanced CFD Codes for Aircraft Design and Development at NAL

Development of Computational Fluid Dynamics (CFD) has now reached a state of maturity, which enables it to simulate the flow past practical aircraft configurations. It can thus play a very useful role in aircraft design and development. CFD codes can be used to determine the aerodynamic loads on aircraft and thus provide a necessary input for the structural design. They can also be used to study and optimize the flow patterns and thus help design an aerodynamically efficient shape. Advanced level multi-block Euler and Navier-Stokes codes with multi-block grid generation package developed at National Aerospace Laboratories (NAL) are introduced here and their applications in analysis and design & development of practical aerospace configurations are described in detail.

Separated and vortical flow in aircraft aerodynamics: a CFD perspective

AbstractIn the early era of aviation, Frederick Lanchester was both an inventor and a theoretician driven by the need for a theory of flight that would reduce the guesswork in designing new aircraft. His book Aerodynamics in 1907 laid down the early foundations of such a theory. The theory with contributions from others, notably Ludwig Prandtl, was refined to become the basis for the sleek designs of WWII aircraft brought about with little guesswork. New technology changed aircraft design radically with the increased speed of jet propulsion reaching into the transonic range with nonlinear aerodynamics. In the late 1940s and early 1950s substantial guesswork returned to aircraft design. The legacy of Lanchester et al., however, lived on with the development of computational fluid dynamics (CFD) that could guide designers through nonlinear transonic effects. This article presents a historical sketch of how CFD developed, illustrated with examples explaining some of the difficulties overcome in the design of the first-generation swept-wing transonic fighters. The historical study is forensic CFD in search for the likely explanation of the designer’s choice for the wing shape that went into production a long time ago. The capability of current CFD applied to the aerodynamics of aircraft with slender wings is surveyed. The cases discussed involve flow patterns with coherent vortices over hybrid wings and wings of moderate sweep. Vortex-flow aerodynamics pertains to understanding the interaction of concentrated vortices with aircraft components. Modern Reynolds-Averaged Navier-Stokes (RANS) technology is useful to predict attached flow. But vortex interaction with other vortices and breakdown lead to unsteady, largely separated flow which has been found out of scope for RANS. Direct simulation of the Navier-Stokes equations is out of computational reach in the foreseeable future, and the need for better physical modeling is evident. Both cruise performance and stalling characteristics are influenced by strong interactions. Two important aspects of wing-flow physics are discussed: separation from a smooth surface that creates a vortex, and vortex bursting, the abrupt breakdown of a vortex with a subsequent loss of lift. Vortex aerodynamics of not-so-slender wings encounter particularly challenging problems, and it is shown how the design of early-generation operational aircraft surmounted these difficulties. Through use of forensic CFD, the article concludes with two case studies of aerodynamic design: how the Saab J29A wing maintains control authority near stall, and how the Saab J32 mitigates pitch-up instability at high incidence.

Numerical Study of the Flow Characteristics of Downburst-like Wind over the 3D Hill Using Different Turbulence Models

With the rapid development of computational fluid dynamics (CFD) technology, it has been widely used to study the wind field characteristics of downbursts in mountainous areas. However, there is little guidance on the selection of different turbulence models for simulating downburst wind fields over hills using CFD, and few comparative studies have been conducted. This paper used nine turbulence models to simulate the wind field of a downburst over a 3D quadratic ideal hill. The simulated values of average and transient winds were compared with wind tunnel test data, and the flow characteristics at different moments under a downburst were analyzed. The flow characteristics in the wake region of the downburst over the hill are also quantitatively analyzed using the proper orthogonal decomposition (POD) method. The results show that approximately 85% of the results from the LES and REA models fall within a 30% error range, so the large eddy simulation (LES) model and the realizable k-ε model (REA) are more accurate in simulating the mean wind field, and the transient wind field simulated by the LES model is also in good agreement with the experimental data. In addition, this paper reveals the evolution mechanism of the transient wind field structure over a hill model under a downburst and finds that the first-order mode obtained by POD may be related to the acceleration effect on the hilltop.

Physics-Informed Neural Network for Flow Prediction Based on Flow Visualization in Bridge Engineering

Wind loads can endanger the safety and stability of bridges, especially long-span cable-supported bridges. Therefore, it is important to evaluate the potential wind loads during the bridge design stage. Traditionally, wind load evaluation is performed by wind tunnel testing, which is relatively expensive. With the development of computational fluid dynamics and high-performance computing, numerical simulations are becoming more accessible for designers. However, the costs required for accurate numerical results are still high, especially for high-fidelity simulations. Under this condition, searching for a more efficient method to evaluate the wind loads in bridge wind engineering has become a new goal. It seems that flow visualization is a good entry point. Although flow visualization techniques have been developed in recent years, it remains difficult to extract velocity and pressure fields from images. To address this problem, physics-informed neural networks (PINNs) have been developed and validated. This study establishes a PINN to investigate the two-dimensional viscous incompressible fluid flow passing a generic bridge deck section. Two cases with different Reynolds numbers are tested. After careful training, it is found that the PINN can accurately extract the velocity and pressure fields from the concentration field and predict the drag and lift coefficients. The results demonstrate that PINNs are a promising method for extracting useful flow information from flow visualization data in engineering applications.

Validation of hemodynamic stress calculation in coronary computed tomography angiography versus intravascular ultrasound.

Development in computational fluid dynamics and 3D construction could facilitate the calculation of hemodynamic stresses in coronary computed tomography angiography (CCTA). However, the agreement between CCTA derived stresses and intravascular ultrasound/intravascular coronary angiography (IVUS/ICA)-derived stresses remains undetermined. Thus, the purpose of this study is to investigate if CCTA can serve as alternative to IVUS/ICA for hemodynamic evaluation. In this retrospective study, 13 patients (14 arteries) with unstable angina who underwent both CCTA and IVUS/ICA at an interval of less than 7 days were consecutively included at the Chinese PLA General Hospital within the year of 2021. Slice-level minimal lumen area (MLA), percent area stenosis, velocity, pressure, Reynolds number, wall shear stress (WSS) and axial plaque stress (APS) were determined by both modalities. The agreement between CCTA and IVUS/ICA was assessed using the intraclass correlation coefficient (ICC), Pearson's correlation coefficient and Bland-Altman analysis. CCTA overestimated the degree of area stenosis (50.22%±16.15% vs. 36.41%±19.37%, P=0.004) with the MLA showing no significant difference (5.81±2.24 vs. 6.72±2.04 mm2, P=0.126). No statistical difference was observed in WSS (6.57±6.26 vs. 5.98±5.55 Pa, P=0.420) and APS (16.03±1,159.45 vs. -1.27±890.39 Pa, P=0.691) between CCTA and IVUS. Good correlation was found in velocity (ICC: 0.796, 95% CI: 0.752-0.833), Reynolds number (ICC: 0.810, 95% CI: 0.768-0.844) and WSS (ICC: 0.769, 95% CI: 0.718-0.810), while the ICC of APS was (ICC: 0.341, 95% CI: 0.197-0.458), indicating a relatively poor correlation. CCTA can serve as a satisfactory alternative to the reference standard, IVUS/ICA in morphology simulation and hemodynamic stress calculation, especially in the calculation of WSS.

Current and Future Applications of Computational Fluid Dynamics in Coronary Artery Disease

Hemodynamics interacts with the cellular components of human vessels, influencing function and healthy status. Locally acting hemodynamic forces have been associated—by a steadily increasing amount of scientific evidence—with nucleation and evolution of atherosclerotic plaques in several vascular regions, resulting in the formulation of the ‘hemodynamic risk hypothesis’ of the atherogenesis. At the level of coronary arteries, however, the complexity of both anatomy and physiology made the study of this vascular region particularly difficult for researchers. Developments in computational fluid dynamics (CFD) have recently allowed an accurate modelling of the intracoronary hemodynamics, thus offering physicians a unique tool for the investigation of this crucial human system by means of advanced mathematical simulations. The present review of CFD applications in coronary artery disease was set to concisely offer the medical reader the theoretical foundations of quantitative intravascular hemodynamics—reasoned schematically in the text in its basic (i.e., pressure and velocity) and derived quantities (e.g., fractional flow reserve, wall shear stress and helicity)—along with its current implications in clinical research. Moreover, attention was paid in classifying computational modelling derived from invasive and non-invasive imaging modalities with unbiased remarks on the advantages and limitations of each procedure. Finally, an extensive description—aided by explanatory figures and cross references to recent clinical findings—was presented on the role of near-wall hemodynamics, in terms of shear stress, and of intravascular flow complexity, in terms of helical flow.

Computational fluid dynamics grid technology development

This paper reviews the development of computational fluid dynamics, especially computational aerodynamics. This paper summarizes the achievements of CFD in grid technology, analyzes the existing problems and perplexities, and prospects its development trend. The CFD grid technology includes structured grid, unstructured grid, hybrid grid and overlapping grid.

Development of CFD based model for sodium flow boiling in narrow channel akin to SFR fuel subchannel towards high void fraction regimes

The Sodium cooled fast reactor (SFR) is one of the Gen IV reactor type meant for the highest nuclear safety standards. Understanding of flow boiling heat transfer characteristics of liquid sodium is essential under certain postulated events of SFR. This study is intended towards the development of computational fluid dynamics (CFD) based multiphase flow model for the sodium boiling in SFR subchannel using the finite volume method. The numerical simulations have been performed for the basic two-dimensional domain that has a resemblance with the flow subchannel of SFR fuel subassembly. The sodium boiling inception, the nucleate flow boiling regime, and further the forced convective vaporization regime characteristics are numerically predicted by the Eulerian-Eulerian model (two-fluid model) developed using flow regime based modeling within the Algebraic Interfacial Area Density (AIAD) framework for the interfacial closure correlations. The improved non-equilibrium wall boiling model is implemented for wall heat flux partitioning. The liquid turbulence is modeled using a Realizable k-ε model with standard wall function. The CFD simulations are performed for the reference experimental cases of liquid sodium flow boiling in narrow annuli and a tubular channel till high void fraction regimes using the model developed. The predictions of void growth behavior along the axial and in the radial direction depict the dominance of annular flow boiling pattern as observed in sodium flow boiling experiments based on the literature. The numerical predictions for the sodium two-phase flow pressure drop are compared with the experimental results and also with the existing empirical correlations. The mechanistic model-based predictions for boiling heat transfer coefficient are obtained from the wall heat balance model and compared with the available empirical correlations. Also based on the flow parameters predicted the possible flow patterns are identified using the available flow regime maps.

Development of Computational Fluid Dynamics (Cfd) Methodology for Characterization of Exhalation Delivery System (Eds) Performance

Development of Computational Fluid Dynamics (Cfd) Methodology for Characterization of Exhalation Delivery System (Eds) Performance

Computer Simulation of Water Flow Animation Based on Two-Dimensional Navier-Stokes Equations

Simulation of water flow animation is a significant and challenging subject in computer graphics. With the continuous development of computational fluid dynamics and computer graphics, many more effective simulation methods have been developed, and fluid animation simulation has developed rapidly. In order to obtain realistic flow animation, one of the key aspects is to simulate flow motion. Based on the two-dimensional Navier-Stokes equations, a mathematical model is established to solve the boundary conditions required by the physical flow field of water. The coordinate transformation formula is introduced to transform the irregular physical area into a regular square calculation area, and then, the specific expressions of the liberalized Navier-Stokes equation, continuity equation, pressure Poisson equation, and dimensionless boundary conditions are given. Using animation software to sequence graphics and images of all kinds of control and direct operation of the relevant instructions, through the computer technology to simulate the flow of animation, based on the stability of fluid simulation method and simulation efficiency, so as to make realistic flow animation. The results show that FluidsNet has considerable performance in accelerating large scene animation simulation on the basis of ensuring the rationality of prediction, and the motion of water wave is realistic. The application of computer successfully simulates water flow.

CFD Analysis on Effect of Angulation in A Healthy Abdominal Aorta-Renal Artery Junction

The recent developments in computational fluid dynamics (CFD) can be useful in observing the detailed haemodynamics in renal artery bifurcation for clinical evaluation and treatment. The present study focuses on haemodynamic behaviour of blood as it flows through the abdominal aorta-renal artery junction in an idealistic healthy artery with varying bifurcation angles to the abdominal aorta, i.e. from 30° to 90° with increments of 15°. This is to examine the effect of angulation on the junction and to determine whether arterial geometry plays a role in the prediction of atherosclerotic lesions. The three-dimensional models used in this study were generated using ANSYS WORKBENCH 19.0, and numerical simulation was done using FLUENT 19.0 solver. The blood flow is assumed to be Newtonian, incompressible and laminar. Haemodynamic parameters such as velocity, wall pressure and wall shear stress along with flow variation are compared among the different models. As the angulation increased, velocity and wall shear stress at the ostial region decreased by 14% and 52% respectively. Wall pressure at the same region saw an increase by 3%. Therefore, renal arteries with higher bifurcating angles to the abdominal aorta were observed to be more prone to the formation of atherosclerotic lesions. The present study is a precursor for future studies on renal artery with stenosis.

Numerical Simulation and Wind Tunnel Investigation on Static Characteristics of VAWT Rotor Starter with Lift-Drag Combined Structure

In order to get rid of the impact of the global financial crisis and actively respond to global climate change, it has become a common choice for global economic development to develop clean energy such as wind energy, improve energy efficiency and reduce greenhouse gas emissions. With the advantages of simple structure, unnecessary facing the wind direction, and unique appearance, the vertical axis wind turbine (VAWT) attracts extensive attention in the field of small and medium wind turbines. The lift-type VAWT exhibits outstanding aerodynamic characteristics at a high tip speed ratio, while the starting characteristics are generally undesirable at a low wind speed; thus, how to improve the starting characteristics of the lift-type VAWT has always been an important issue. In this paper, a lift-drag combined starter (LDCS) suitable for lift-type VAWT was proposed to optimize the starting characteristics of lift-type VAWT. With semi-elliptical drag blades and lift blades equipped on the middle and rear part outside the starter, the structure is characterized by lift-drag combination, weakening the adverse effect of the starter with semi-elliptical drag blades alone on the output performance of the original lift-type VAWT and improving the characteristics of the lift-drag combined VAWT. The static characteristic is one of the important starting characteristics of the wind turbine. The rapid development of computational fluid dynamics has laid a solid material foundation for VAWT. Thus the static characteristics of the LDCS with different numbers of blades were investigated by conducting numerical simulation and wind tunnel tests. The results demonstrated that the static torque coefficient of LDCS increased significantly with the increased incoming wind speed. The average value of the static torque coefficient also increased significantly. This study can provide guidelines for the research of lift-drag combined wind turbines.

Numerical simulation of single-phase heat transfer and nucleate boiling of liquid sodium in narrow annulus channel similar to that of SFR fuel subchannel

The sodium cooled fast reactor (SFR) is a Generation IV nuclear reactor that uses fast neutrons for fission and liquid sodium as the coolant for fission heat removal. Compared to conventional fluids, such as water, liquid sodium shows superior performance in heat transfer because of its high thermal conductivity and low Prandtl number. Understanding of single-phase and two-phase heat transfer characteristics of liquid sodium is essential for the analysis of the normal operation and certain postulated accidental events of SFR. This study is intended towards the development of computational fluid dynamics (CFD) based multiphase models for the safety analysis of SFR using the finite volume method. The numerical simulations of single-phase and two-phase heat transfer processes have been performed for the basic two-dimensional domain that has resemblance with the flow subchannel of SFR fuel subassembly. This study deals with heat transfer considerations under low Peclet number at high temperature, and its boiling inception and further to the nucleate boiling regime in a narrow vertical annulus channel. The Realizable k-ε model with Kays correlation for the turbulent Prandtl number better predicts the single-phase heat transfer characteristics under low Peclet number. A correlation for Nusselt number is fitted from the numerical results for low Peclet number flow conditions in an annulus channel. The flow boiling inception and nucleate boiling are numerically predicted by the Eulerian-Eulerian multiphase model with non-equilibrium wall-boiling for wall heat flux partitioning. The turbulence is modeled using Realizable k-ε model with standard wall function. Under the flow and heat flux values considered the near steady-state boiling conditions are predicted without much pulsating behavior as observed in the reference experiments and during this, the two-phase flow pattern varied from inception to the nucleate boiling regime. The mechanistic model based heat transfer coefficient is evaluated in the boiling zone from the flux partitioning components and compared with the available empirical correlations.

The design and energy saving effect prediction of rudder-bulb-fin device based on CFD and model test

Recent developments in Computational Fluid Dynamics (CFD) and high-performance computer hardware have made it possible to design Energy Saving Devices (ESDs) using numerical methods. The present work investigates the influence of rudder bulb diameter, thrust fin; span, chord length and angle of attack on propulsive efficiency. In order to increase computational efficiency, a hypothesis was developed and a quick estimate method for design parameters and the optimization procedure. Bare hull resistance, propeller open water performance and interaction of hull-propeller-rudder simulations were carried out using CFD code to solve Reynolds Averaged Navier-Stokes (RANS) equations. A validation study shows a good agreement between the CFD and experimental data. Model tests were carried out using optimum parameters for rudder bulb and rudder attached thrust fins. Comparison of the propulsive efficiency between the ship with the conventional rudder and ship with the optimized rudder-bulb-fin device was done. The model test predicted energy gains of 2.18% compared to 2.63% gains predicted by the CFD method. This study would be useful during design and optimization of rudder-bulb-fin.

Review and Comparison of Numerical Simulations of Secondary Flow in River Confluences

River confluences are a common feature in natural water resources. The flow characteristics in confluences are complicated, especially at junction areas between tributaries and the main river. One of the typical characteristics of confluences is secondary flow, which plays an important role in mixing, velocity, sediment transport, and pollutant dispersion. In addition to the experimental and field studies that have been conducted in this area, the development of computational fluid dynamics has allowed researchers in this field to use different numerical models to simulate turbulence properties in rivers, especially secondary flows. Nowadays, the hydrodynamics of flows in confluences are widely simulated by using three-dimensional models in order to fully capture the flow structures, as the flow characteristics are considered to be turbulent and three-dimensional at river junctions. Several numerical models have been recommended for this purpose, and various turbulence models have been used to simulate the flows at confluences. To assess the accuracy of turbulence models, flows have been predicted by applying different turbulence models in the numerical model and the results have been compared with other data, such as field, laboratory, and experimental data. The purpose behind these investigations was to find the suitable model for each case of turbulent flow and for different types of confluences. In this study, the performances of turbulence models for confluences are reviewed for different numerical simulation strategies.

Simulation of turbulent mixing rate in simulated subchannels of a reactor rod bundle

Abstract Subchannel analysis codes are widely used for the thermal-hydraulic design of nuclear reactor rod bundle. The effectiveness of subchannel analysis codes depends on turbulent mixing between these subchannels. Turbulent mixing has no direct contribution to the axial mass flow rate through subchannel but it will cause exchange of momentum and energy between the neighboring subchannels. Thus, it is important to evaluate the turbulent mixing coefficient for reactor rod bundle as it is a significant factor in the lateral energy and momentum equation for subchannel analysis codes like COBRA IIIC, COBRA-IV and MATRA LMR-FB. With the rapid developments in computational fluid dynamics and computer performance, three-dimensional analyses of turbulent flows occurring in the nuclear rod bundle have become more prominent. Several numerical analyses have already been attempted to investigate the flow behavior in rod bundles of different reactors. Much of these are dedicated to find out the structure of turbulence in rod bundle but a few analyses has been done to evaluate the magnitude of the turbulent mixing coefficient. In view of this, CFD analyses were carried out to determine the turbulent mixing coefficient in the simulated sub-channels of the reactor rod bundle. Previous studies on the structure of turbulence reveals that it is highly anisotropic. Hence, the Reynolds Stress Model (RSM), finer mesh and near wall distance ( y + ≤ 2) is required to capture turbulent mixing phenomena. The validation of results is done by comparing with subchannel mixing experiments.

Numerical simulation of oxygen transport in land-based aquaculture tank

Dissolved oxygen is an important indicator of the water quality and important for fish survival in aquaculture. The distribution of the dissolved oxygen is highly dependent on the flow motions, the pressure and the temperature of the water. With the development of computational fluid dynamics, the spatial and temporal distribution of dissolved oxygen in water can be predicted to evaluate and maintain the water quality. In the present study, a three-dimensional numerical model for predicting the dissolved oxygen and the water flow motions is developed. Oxygen transport in land-based aquaculture tanks is investigated by solving the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations combined with an additional species transport equation of the dissolved oxygen concentration. The volume of fluid (VOF) method is used to simulate the evolution of two-phase immiscible flows of the water and the air with an interface. The predicted dissolved oxygen concentrations (DOC) are in agreement with the experimental measurement which validate the present numerical model. The evolution of the DOC in the water and the water velocities are discussed based on the numerical simulations.