The cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding,where weak vortices coexist with strong vortices and the strong shear phenomenon also exists at the opening of...The cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding,where weak vortices coexist with strong vortices and the strong shear phenomenon also exists at the opening of the cavity.Therefore,it is of great significance to accurately capture vortices at the opening for the control of the cavity buffeting noise.This paper first compares the Omega vortex identification method with the Q andλ2criteria based on the large eddy simulation(LES)of the backward-facing step flow,and it is found that the Omega method enjoys the following advantages:it is not sensitive to a moderate threshold change andΩ=0.52 can be used as a fixed threshold,it can capture both the strong and weak vortices at the same time;and it will not be contaminated by the shear.Then the Omega(Ω)method is applied to the LES of the cavity buffeting noise:the mechanism of the cavity buffeting noise is studied based on a simple cavity model firstly,and then the effects of the incoming boundary layer thicknesses and the incoming boundary layer shapes on the cavity buffeting noise are analyzed.The results show that:theΩmethod clearly captures the processes of the vortex generation,development,collision and fragmentation,verifying that the generation of the cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding;as the thickness of the incoming boundary layer increases,the free shear layer becomes more stable and the Helmholtz resonance is avoided effectively,thereby the cavity buffeting noise is reduced effectively,adding a convexity upstream of the cavity opening to interfere the shape of the incoming boundary layer to reduce the acoustic feedback effect can reduce the cavity buffeting noise effectively.展开更多
The water contamination on the side windows of moving vehicles is a crucial issue in improving the driving safety and the comfort.In this paper,an effective optimization method is proposed to reduce the water contamin...The water contamination on the side windows of moving vehicles is a crucial issue in improving the driving safety and the comfort.In this paper,an effective optimization method is proposed to reduce the water contamination on the side windows of automobiles.The accuracy and the efficiency of the numerical simulation are improved by using the lattice Boltzmann method,and the Lagrangian particle tracking method.Optimized parameters are constructed on the basis of the occurrence of the water deposition on a vehicle’s side window.The water contamination area of the side window and the aerodynamic drag are considered simultaneously in the design process;these two factors are used to form the multi-objective optimization function in the genetic algorithm(GA)method.The approximate model,the boundary-seeded domain method,and the GA method are combined in this study to enhance the optimization efficiency.After optimization,the optimal parameters for the A-pillar section are determined by setting the boundary to an area of W=7.77 mm,L=1.27 mm and H=11.22 mm.The side window’s soiling area in the optimized model is reduced by 66.93%,and the aerodynamic drag is increased by 0.41%only,as compared with the original model.It is shown that the optimization method can effectively solve the water contamination problem of side windows.展开更多
基金the Natural Nature Science Foundation of China(Grant No.51875238).
文摘The cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding,where weak vortices coexist with strong vortices and the strong shear phenomenon also exists at the opening of the cavity.Therefore,it is of great significance to accurately capture vortices at the opening for the control of the cavity buffeting noise.This paper first compares the Omega vortex identification method with the Q andλ2criteria based on the large eddy simulation(LES)of the backward-facing step flow,and it is found that the Omega method enjoys the following advantages:it is not sensitive to a moderate threshold change andΩ=0.52 can be used as a fixed threshold,it can capture both the strong and weak vortices at the same time;and it will not be contaminated by the shear.Then the Omega(Ω)method is applied to the LES of the cavity buffeting noise:the mechanism of the cavity buffeting noise is studied based on a simple cavity model firstly,and then the effects of the incoming boundary layer thicknesses and the incoming boundary layer shapes on the cavity buffeting noise are analyzed.The results show that:theΩmethod clearly captures the processes of the vortex generation,development,collision and fragmentation,verifying that the generation of the cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding;as the thickness of the incoming boundary layer increases,the free shear layer becomes more stable and the Helmholtz resonance is avoided effectively,thereby the cavity buffeting noise is reduced effectively,adding a convexity upstream of the cavity opening to interfere the shape of the incoming boundary layer to reduce the acoustic feedback effect can reduce the cavity buffeting noise effectively.
基金Project supported by the National Science Foundation of China(Grant No.51875238).
文摘The water contamination on the side windows of moving vehicles is a crucial issue in improving the driving safety and the comfort.In this paper,an effective optimization method is proposed to reduce the water contamination on the side windows of automobiles.The accuracy and the efficiency of the numerical simulation are improved by using the lattice Boltzmann method,and the Lagrangian particle tracking method.Optimized parameters are constructed on the basis of the occurrence of the water deposition on a vehicle’s side window.The water contamination area of the side window and the aerodynamic drag are considered simultaneously in the design process;these two factors are used to form the multi-objective optimization function in the genetic algorithm(GA)method.The approximate model,the boundary-seeded domain method,and the GA method are combined in this study to enhance the optimization efficiency.After optimization,the optimal parameters for the A-pillar section are determined by setting the boundary to an area of W=7.77 mm,L=1.27 mm and H=11.22 mm.The side window’s soiling area in the optimized model is reduced by 66.93%,and the aerodynamic drag is increased by 0.41%only,as compared with the original model.It is shown that the optimization method can effectively solve the water contamination problem of side windows.
