| With the development of our technology,vehicle have become a necessary means of transportation for people's lives.The status of flow near the wheel is the important point of auto aerodynamics research.Among the aerodynamic problems of wheels,the motion condition of wheels is the most important problem.Rotating wheels will influence people to evaluate the car on the automobile aerodynamics.Rotating wheels have a huge impact on aerodynamic drag,aerodynamic noise,thermal management and water management,etc..Although there are many methods to make wheel rotate in simulation,each method has advantages and disadvantages,which will affect the evaluation of the vehicle aerodynamics.Therefore,it is a great significance to study the characteristics of rotating wheels methods and find methods that reflect actual motion to study the effect of rotating wheels on aerodynamic drag.Based on the CFD simulation method,the computational fluid dynamics software STAR-CCM + is used to study the flow field near the wheel rotation.The main research contents are as follows:(1)Firstly,it is found that the mechanism of rotation will change the position of the separation point by computing the rotation of the cylinder.Then rotation affects the pressure difference before and after the model and changes the status of the flow.(2)Secondly,the DrivAer model is used as the research object.Through the wind tunnel experiment PIV technology,study the effect of rotation on the flow field structure.It is found that there are more regular flow replace irregular turbulent flow behind wheel while the wheel is rotating.The size of vortex becomes smaller or even disappears and the vortex position moves backward while car's four wheels are rotating.(3)Thirdly,study the differences between different rotation methods.The simulation results are compared with experimental data to verify the correctness of the simulation methods.Contrasting and analyzing of Rotating Wall(RW),Multiple Reference Frame(MRF)and Sliding Mesh(SM),explore the differences of different rotation simulation methods.Theresearch results show that there is a big difference in the flow field near the wheel obtained by different rotation methods.The captured flow field information is also quite different.The root cause is the difference in algorithm.The RW method only calculates the grid nodes by giving angular velocity.Some lateral surface flow fields of the wheels do not flow correctly.The MRF method introduces a reference coordinate system for rotation.The pressure gradient is brought,at the same time,only the numerical coordinate system is rotated.The SM method is a grid rotation motion in real time,which truly reflects the motion conditions.However,the same as the MRF method,it cannot handle the wheels contact with the ground while they are rotating.According to their respective advantages and disadvantages,the rotation methods are combined,which two combination methods are found: SMRW method(SM and RW,SMRW)and MFRRW method(MRF and RW,MFRRW).By comparing the computed Cd with the existing experiment data,the study found that the two methods have almost no restrictions.The MFRRW method has a large error with the experiment data.The SMRW method has a high accuracy within the allowable error.At last,the SMRW method is determined to be this article simulation method.(4)Finally,study the effects of wheel rotation on the flow by computing different shapes of DrivAer models.This paper apply the SMRW method to study the effect of wheel rotation on the flow.Study the influence of wheel rotation on the aerodynamics of the vehicle under different shape and speed factors.The research shows that the wheel rotation has a lower Cd than when the wheel is stationary.The wheel rotation directly drives the airflow around the wheel to reduce the airflow stagnation area.The flow at the bottom of the car and the flow at the rear of the car are influenced by wheel rotation.The Notchback and Fastback decrease basically the same but the Estateback drop is the smallest. |
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