Research On Numerical Simulation Of Aerodynamic Noise Of Commercial Vehicle Based On External Flow And Interior Acoustic Field

Vehicle NVH is a durable research problem.With the increase of vehicle speed,aerodynamic noise which account for the overall car noise is outstanding.Therefore,aerodynamic noise has become the focus of research by automobile companies and research universities.Research on aerodynamic noise mainly includes wind tunnel test method,numerical simulation method and real vehicle sliding test.The numerical simulation can clearly know the flow field of the surface on the car body during the research stage of the car,and provide engineering application methods to reduce the aerodynamic noise and aerodynamic drag of the car.This article takes a domestic brand commercial vehicle as the research object,and the STAR-CCM+ and LMS.VIRTUAL.LAB were adopted to conduct joint simulation of the flow field and sound field of the cab and vehicle.The effect of rear-view mirror on the aerodynamic noise in the cab and the aerodynamic drag of the vehicle are studied by analyzing the external flow field and internal sound field of the car.Firstly,based on the cab of a commercial vehicle,the numerical simulation of the flow field in the rear-view mirror area and the prediction of interior noise were carried out.Steady-state analysis uses the SST(Menter)in the RANS model,and transient analysis uses the SST(Menter)based detached-eddy simulation(DES).The mechanism of turbulent pressure pulsation on the window surface with the A-pillar and rear-view mirror was revealed by analyzing the transient flow field data in the side window area of the rear-view mirror.The turbulent pressure pulsation load on the two sides' window surface was solved meanwhile.Acoustic vibration coupling was used to calculate the propagation of aerodynamic noise by using the turbulent pressure pulsation on the window surface as a boundary condition.Based on the distribution of cab interior acoustic field,the change regulation of aerodynamic noise and the most area of sound pressure level in middle and low frequency band were showed.The regulation of driver's right ear of the sound pressure level in the frequency range of 20-2500 Hz was obtained moreover.The real vehicle road slide test shows that the aerodynamic noise is gradually obvious when the vehicle speed is80-110 km / h;the trend of the sound pressure level curve when the vehicle speed is100km/h is consistent with the simulation prediction results.The computational fluid dynamics(CFD)coupling with acoustic vibration can accurately predict the sound pressure level of aerodynamic noise in the vehicle cab.Secondly,the models with or without the rear-view mirror were selected for simulation to discuss the effect of the exterior rear-view mirror on the aerodynamic noise in the cab and the wind drag of the vehicle.Comparing the data of the outside transient velocity flow field and interior sound field of the two models,the rear-view mirror changes the flow field in the rear-view mirror area,affecting the acoustic environment in the cab.The noise of without the rear-view mirror was low.The wind drag coefficient,the wind drag's development curve and speed cloud were analyzed,it can be seen that the Cd is as high as 0.635 without the rear-view mirror,which is much higher than 5.9% with it.The vehicle Cd is increased at the rear-view mirror and cabin,and the other parts are the same.The increasing of Cd at the rear-view mirror is because the rear-view mirror guides the airflow from the A-pillar and reduces the vortex mass;the Cd in the cabin is rising due to the airflow separated from the A-pillar impacts the cabin.The rear-view mirror can improve the airflow impacting the cabin.Furthermore,based on cab and vehicle models of 4 rear-view mirrors,the joint simulation research method is used to study the external flow field and internal sound field of the car.The gap of the rear-view mirror lens,mirror cover,position of the windward surface,and regularity have a more obvious influence on the wind drag of the vehicle and the turbulent pressure pulsation in the window area.The effect of different rear-view mirrors on the aerodynamic noise in the car and distribution of the sound pressure level cloud in the four rear-view mirrors is analyzed by calculating the propagation of turbulent pressure to the aerodynamic noise in the car,and the flow field and sound field are verified consistency.The sound pressure level curve of the driver's right ear intuitively illustrates the effect of different rear-view mirrors on the driver.Studies have shown that rear-view mirror styling affects the flow field in the rear-view mirror area and the acoustic space environment in the car.Proper adjustment and optimization of the styling parameters can effectively reduce the impact of the rear-view mirror on the aerodynamic noise in the car and the wind resistance of the vehicle.In summary,the co-simulation model established in this paper can more accurately predict the aerodynamic noise in the cab,and the mechanism of the aerodynamic noise and wind drag generated by the rear-view mirror were expounded.The effect of rear-view mirror modeling factors on aerodynamic noise and aerodynamic drag was explored.The reference was provided for optimization and development of rear-view mirrors.