This review addresses four key themes in automotive aerodynamics:flow instability in the wheel region,the aerodynamic characteristics of rims,the aerodynamic behavior of tires,and drag reduction strategies based on fl...This review addresses four key themes in automotive aerodynamics:flow instability in the wheel region,the aerodynamic characteristics of rims,the aerodynamic behavior of tires,and drag reduction strategies based on flow control around the wheels.The wheel region,comprising the tire,rim,and adjacent aerodynamic components,typically represents the major source of vehicle drag owing to the inherently complex flow generated by wheel rotation,tread geometry,and rim design,which gives rise to flow separation,vortex shedding,and turbulence.Drawing on a broad body of experimental and numerical research,this review elucidates the mechanisms governing such dynamics,and considers drag mitigation techniques,including biomimetic surface treatments and multi-element flow control concepts.Particular emphasis is placed on enclosed-spoke rims,rim-edge enclosures,and non-smooth tire microstructures,which have consistently demonstrated notable drag reduction potential.The review further identifies critical shortcomings in current research,most notably the lack of quantitative analyses of aerodynamic energy losses and the absence of integrated optimization strategies that jointly address tire,rim,and fender design.展开更多
We introduce a corrected sinusoidal-wave drag force method （SDFM） into optical tweezers to calibrate the trapping stiffness of the optical trap and conversion factor （CF） of photodetectors. First, the theoretical ...We introduce a corrected sinusoidal-wave drag force method （SDFM） into optical tweezers to calibrate the trapping stiffness of the optical trap and conversion factor （CF） of photodetectors. First, the theoretical analysis and experimental result demonstrate that the correction of SDFM is necessary, especially the error of no correction is up to 11.25% for a bead of 5μm in diameter. Second, the simulation results demonstrate that the SDFM has a better performance in the calibration of optical tweezers than the triangular-wave drag force method （TDFM） and power spectrum density method （PSDM） at the same signal-to-noise ratio or trapping stiffness. Third, in experiments, the experimental standard deviations of calibration of trapping stiffness and CF with the SDFM are about less than 50% of TDFM and PSDM especially at low laser power. Finally, the experiments of stretching DNA verify that the in situ calibration with the SDFM improves the measurement stability and accuracy.展开更多
Considering current space debris situation in outer space environment,different methods for debris removal missions are proposed.In addition,advanced technologies are needed to be demonstrated for future human space e...Considering current space debris situation in outer space environment,different methods for debris removal missions are proposed.In addition,advanced technologies are needed to be demonstrated for future human space exploration programs.The main issue regarding to these missions is high mission cost for both debris removal missions and space environmental tests to achieve high maturity level for new space-usable technologies.Since,these missions are unavoidable for future of human space activities,a solution which can tackle these challenges is necessary.This paper will address to an idea which has the possibility to give a solution for facilitating technology readiness level(TRL)maturity tests by debris removal mission platform consideration.展开更多
The aim of this work is to build a 3D numerical model to study the characteristics of passive drag on competitive swimmers taking into account the impact of the free surface. This model solves the 3D incompressible Na...The aim of this work is to build a 3D numerical model to study the characteristics of passive drag on competitive swimmers taking into account the impact of the free surface. This model solves the 3D incompressible Navier-Stokes equations using RNG k-ε turbulence closure. The volume of fluid（VOF） method is used to locate the free surface. The 3D virtual model is created by Computer Aided Industrial Design（CAID） software, Rhinoceros. Firstly, a specific posture of swimming is studied. The simulation results are in good agreement with the data from mannequin towing experiments. The effects of a swimmer＇s arms and legs positions on swimming performance are then studied. Finally, it is demonstrated that the present method is capable of simulating gliding near the free surface.展开更多
A meshless Element-Free Galerkin （EFG） method was used to directly simulate the fluidization process in two dimensions. The drag force on particles was obtained by integrating the stress and shear forces on the part...A meshless Element-Free Galerkin （EFG） method was used to directly simulate the fluidization process in two dimensions. The drag force on particles was obtained by integrating the stress and shear forces on the particle surfaces. The results show that meshless methods are capable of dealing with real particle collisions, thus are superior to most mesh-based methods in reflecting the fluidization process with frequent particle collisions and suitable void fractions. Particle distribution greatly influences the drag coefficients even for the same voidage, that is, there are large differences in the average drag coefficients between nonuniform and uniform particle distributions. Different compacting directions also have different regu- larities, so conventional formulas such as ＇Wen and Yu＇ and ＇Felice＇ models have some deviations in such nonuniform distributions. To evaluate the influence of the nonuniformity, the drag force in multiple particle systems was simulated by using nonuniformity coefficients, Cvx and Cvy, to quantitatively describe the nonuniform distribution in different directions. Drag force during fluidization can be successfully evaluated by the use of Cvx alone.展开更多
The lattice Boltzmann method （LBM） has gained increasing popularity in the last two decades as an alternative numerical approach for solving fluid flow problems. One of the most active research areas in the LBM is i...The lattice Boltzmann method （LBM） has gained increasing popularity in the last two decades as an alternative numerical approach for solving fluid flow problems. One of the most active research areas in the LBM is its application in particle-fluid systems, where the advantage of the LBM in efficiency and parallel scalability has made it superior to many other direct numerical simulation （DNS） techniques. This article intends to provide a brief review of the application of the LBM in particle-fluid systems. The numerical techniques in the LBM pertaining to simulations of particles are discussed, with emphasis on the advanced treatment for boundary conditions on the particle-fluid interface. Other numerical issues, such as the effect of the internal fluid, are also briefly described. Additionally, recent efforts in using the LBM to obtain closures for particle-fluid drag force are also reviewed.展开更多
The wind field and pollutant dispersion are predicted numerically in a local urban area with crowded buildings and heavy traffic.A domain decomposition method is used in the large eddy simulation,in which the urban ar...The wind field and pollutant dispersion are predicted numerically in a local urban area with crowded buildings and heavy traffic.A domain decomposition method is used in the large eddy simulation,in which the urban area is decomposed into a central area,where pollution is the major concern,and a surrounding region,where the pollutant distribution is not important.The composite model is proposed for the complex building-street layout.The fine grid mesh is used to resolve the buildings in the central area while the buildings are treated as roughness elements in the surrounding region where the coarse grids are used.The proposed numerical method is applied to simulate the wind field and pollutant dispersion from vehicle exhaust in the Rua Do Campo area of Macao.The results show that the composite model is an appropriate method for predicting wind field and pollutant dispersion in the crowded building area.展开更多
lnterphase momentum transport in heterogeneous gas-solid systems with multi-scale structure is of great importance in process engineering. In this article, lattice Boltzmann simulations are performed on graphics proce...lnterphase momentum transport in heterogeneous gas-solid systems with multi-scale structure is of great importance in process engineering. In this article, lattice Boltzmann simulations are performed on graphics processing units （GPUs）, the computational power of which exceeds that of CPUs by more than one order of magnitude, to investigate incompressible Newtonian flow in idealized multi-scale particle-fluid systems. The structure consists of a periodic array of clusters, each constructed by a bundle of cylinders. Fixed pressure boundary condition is implemented by applying a constant body force to the flow through the medium. The bounce-back scheme is adopted on the fluid-solid interfaces, which ensures the no-slip boundary condition. The structure is studied under a wide range of particle diameters and packing fractions, and the drag coefficient of the structure is found to be a function of voidages and fractions of the clusters, besides the traditional Reynolds number and the solid volume fractions. Parameters reflecting multi-scale characters are, therefore, demonstrated to be necessary in quantifying the drag force of heterogeneous gas-solid system. The numerical results in the range 0.1 〈 Re 〈 10 and 0 〈 Ф 〈 0.25 are compared with Wen and Yu＇s correlation, Gibilaro equation, EMMS-based drag model, the Beetstra correlation and the Benyahia correlation, and good agreement is found between the simulations and the EMMS-based drag model for heterogeneous systems.展开更多
基金funded by the National Natural Science Foundation of China,grant numbers 52072156,52272366the Postdoctoral Foundation of China,grant number 2020M682269.
文摘This review addresses four key themes in automotive aerodynamics:flow instability in the wheel region,the aerodynamic characteristics of rims,the aerodynamic behavior of tires,and drag reduction strategies based on flow control around the wheels.The wheel region,comprising the tire,rim,and adjacent aerodynamic components,typically represents the major source of vehicle drag owing to the inherently complex flow generated by wheel rotation,tread geometry,and rim design,which gives rise to flow separation,vortex shedding,and turbulence.Drawing on a broad body of experimental and numerical research,this review elucidates the mechanisms governing such dynamics,and considers drag mitigation techniques,including biomimetic surface treatments and multi-element flow control concepts.Particular emphasis is placed on enclosed-spoke rims,rim-edge enclosures,and non-smooth tire microstructures,which have consistently demonstrated notable drag reduction potential.The review further identifies critical shortcomings in current research,most notably the lack of quantitative analyses of aerodynamic energy losses and the absence of integrated optimization strategies that jointly address tire,rim,and fender design.
基金supported by the National Natural Science Foundation of China(Grant Nos.11302220,11374292,and 31100555)the National Basic Research Program of China(Grant No.2011CB910402)
文摘We introduce a corrected sinusoidal-wave drag force method （SDFM） into optical tweezers to calibrate the trapping stiffness of the optical trap and conversion factor （CF） of photodetectors. First, the theoretical analysis and experimental result demonstrate that the correction of SDFM is necessary, especially the error of no correction is up to 11.25% for a bead of 5μm in diameter. Second, the simulation results demonstrate that the SDFM has a better performance in the calibration of optical tweezers than the triangular-wave drag force method （TDFM） and power spectrum density method （PSDM） at the same signal-to-noise ratio or trapping stiffness. Third, in experiments, the experimental standard deviations of calibration of trapping stiffness and CF with the SDFM are about less than 50% of TDFM and PSDM especially at low laser power. Finally, the experiments of stretching DNA verify that the in situ calibration with the SDFM improves the measurement stability and accuracy.
基金Supported by the National Natural Science Foundation of China(11572037)
文摘Considering current space debris situation in outer space environment,different methods for debris removal missions are proposed.In addition,advanced technologies are needed to be demonstrated for future human space exploration programs.The main issue regarding to these missions is high mission cost for both debris removal missions and space environmental tests to achieve high maturity level for new space-usable technologies.Since,these missions are unavoidable for future of human space activities,a solution which can tackle these challenges is necessary.This paper will address to an idea which has the possibility to give a solution for facilitating technology readiness level(TRL)maturity tests by debris removal mission platform consideration.
基金financially supported by the Fundamental Research Funds for the Central Universities of China
文摘The aim of this work is to build a 3D numerical model to study the characteristics of passive drag on competitive swimmers taking into account the impact of the free surface. This model solves the 3D incompressible Navier-Stokes equations using RNG k-ε turbulence closure. The volume of fluid（VOF） method is used to locate the free surface. The 3D virtual model is created by Computer Aided Industrial Design（CAID） software, Rhinoceros. Firstly, a specific posture of swimming is studied. The simulation results are in good agreement with the data from mannequin towing experiments. The effects of a swimmer＇s arms and legs positions on swimming performance are then studied. Finally, it is demonstrated that the present method is capable of simulating gliding near the free surface.
基金supported by the National Natural Science Foundation of China (No. 51076083)
文摘A meshless Element-Free Galerkin （EFG） method was used to directly simulate the fluidization process in two dimensions. The drag force on particles was obtained by integrating the stress and shear forces on the particle surfaces. The results show that meshless methods are capable of dealing with real particle collisions, thus are superior to most mesh-based methods in reflecting the fluidization process with frequent particle collisions and suitable void fractions. Particle distribution greatly influences the drag coefficients even for the same voidage, that is, there are large differences in the average drag coefficients between nonuniform and uniform particle distributions. Different compacting directions also have different regu- larities, so conventional formulas such as ＇Wen and Yu＇ and ＇Felice＇ models have some deviations in such nonuniform distributions. To evaluate the influence of the nonuniformity, the drag force in multiple particle systems was simulated by using nonuniformity coefficients, Cvx and Cvy, to quantitatively describe the nonuniform distribution in different directions. Drag force during fluidization can be successfully evaluated by the use of Cvx alone.
文摘The lattice Boltzmann method （LBM） has gained increasing popularity in the last two decades as an alternative numerical approach for solving fluid flow problems. One of the most active research areas in the LBM is its application in particle-fluid systems, where the advantage of the LBM in efficiency and parallel scalability has made it superior to many other direct numerical simulation （DNS） techniques. This article intends to provide a brief review of the application of the LBM in particle-fluid systems. The numerical techniques in the LBM pertaining to simulations of particles are discussed, with emphasis on the advanced treatment for boundary conditions on the particle-fluid interface. Other numerical issues, such as the effect of the internal fluid, are also briefly described. Additionally, recent efforts in using the LBM to obtain closures for particle-fluid drag force are also reviewed.
基金the National Natural Science Foundation of China(Grant No. 10872109)the Foundation for Development of Science and Technology in Macao(Grant No. FDCT 055/2005/A)the Supercomputing Center of Chinese Academy of Sciences
文摘The wind field and pollutant dispersion are predicted numerically in a local urban area with crowded buildings and heavy traffic.A domain decomposition method is used in the large eddy simulation,in which the urban area is decomposed into a central area,where pollution is the major concern,and a surrounding region,where the pollutant distribution is not important.The composite model is proposed for the complex building-street layout.The fine grid mesh is used to resolve the buildings in the central area while the buildings are treated as roughness elements in the surrounding region where the coarse grids are used.The proposed numerical method is applied to simulate the wind field and pollutant dispersion from vehicle exhaust in the Rua Do Campo area of Macao.The results show that the composite model is an appropriate method for predicting wind field and pollutant dispersion in the crowded building area.
基金financially supported by the National Natural Science Foundation of China under Grant Nos.: 20821092 and 20906091the Ministry of Science and Technology under Grant Nos.: 2008BAF33B01 and 2007DFA41320the Chinese Academy of Sciences under Grant No. KGCX2-YW-124
文摘lnterphase momentum transport in heterogeneous gas-solid systems with multi-scale structure is of great importance in process engineering. In this article, lattice Boltzmann simulations are performed on graphics processing units （GPUs）, the computational power of which exceeds that of CPUs by more than one order of magnitude, to investigate incompressible Newtonian flow in idealized multi-scale particle-fluid systems. The structure consists of a periodic array of clusters, each constructed by a bundle of cylinders. Fixed pressure boundary condition is implemented by applying a constant body force to the flow through the medium. The bounce-back scheme is adopted on the fluid-solid interfaces, which ensures the no-slip boundary condition. The structure is studied under a wide range of particle diameters and packing fractions, and the drag coefficient of the structure is found to be a function of voidages and fractions of the clusters, besides the traditional Reynolds number and the solid volume fractions. Parameters reflecting multi-scale characters are, therefore, demonstrated to be necessary in quantifying the drag force of heterogeneous gas-solid system. The numerical results in the range 0.1 〈 Re 〈 10 and 0 〈 Ф 〈 0.25 are compared with Wen and Yu＇s correlation, Gibilaro equation, EMMS-based drag model, the Beetstra correlation and the Benyahia correlation, and good agreement is found between the simulations and the EMMS-based drag model for heterogeneous systems.
