The Investigation On Interior Noise Of Electric Vehicle Induced By Underbody Flow Based On Modal Acoustic Transfer Vector Method

With the continuous reduction of powertrain noise and road excitation noise,wind noise has become the main source of interior noise of high-speed electric vehicle.At present,the influence of high-speed underbody airflow on the interior noise of electric vehicle is gradually prominent due to the effective control of wind noise induced by the air separation near rear-view mirror,A-pillar,and the decreasing thickness of underbody floor caused by vehicle lightweight.In this thesis,the characteristics and control methods of interior noise of electric vehicle induced by underbody flow are investigated by numerical simulation method(CFD/FEM,CFD/MATV and SNGR).The main contents are as follows:The reliability of the simulation methods is verified based on simple car model.The sound pressure level of the monitoring points in the model is predicted by CFD/FEM method,and compared with the wind tunnel test results.The modal acoustic transfer vector is calculated based on the simulation results of CFD/FEM method,and the sound pressure level of the same monitoring point with different vehicle speed is predicted by CFD/MATV method,and compared with the wind tunnel test results.The simulation of underbody flow-induced interior noise of electric vehicle is conducted by CFD/FEM method,and the characteristics of underbody flow-induced interior noise and modal sound transfer vector of wind noise transmitted from underbody floor to vehicle is analyzed by the results of CFD/FEM simulation and modal analysis of underbody and cavity.The control effects of underbody flow-induced interior noise of electric vehicle with different underbody aerodynamics accessories(front cabin underbody cover,front wheel air baffle,and air dam)are investigated by SNGR and CFD/MATV methods.In addition,the noise reduction mechanism of each noise reduction scheme is analyzed through the results of flow field and sound field simulation.The results show that: compared with the FEM method,the calculation efficiency of MATV method on interior sound field is improved by 96%.For electric vehicle,the airflow separation under the front cabin is particularly serious,which is the main source of underbody flow-induced interior noise.The interior noise increases first and then decreases with the increase of frequency,and mainly concentrates in the low frequency band between 100-200 Hz.Meanwhile,with the increase of frequency,the modal sound transfer vector also increases first and then decreases.All of the underbody cover,the front wheel air baffle and air dam improves the flow field disturbance under the front cabin and achieve interior noise reduction.With the installing of underbody cover and front wheel air baffle,the total sound pressure level of the nterior monitoring points is reduced by 3.45 d B and 2.30 d B,respectively.The control effect of air dams with different shapes on underbody flow-induced interior noise differs greatly.The long strip air dam forms more resistance for the incoming underbody flow,thus has the best control effect,achieving 3.14 d B reduction.The noise reduction of triangular toothed gas dam and rectangular toothed gas dam is 2.26 d B and 1.87 d B,respectively.