Research On The Effect Of Bionic Rearview Mirror With Sawtooth Edge To Aerodynamic Noise

Wind noise generated by speeding cars brings negative effect on people’s life. Asblunt bodies on the car surface, outside rear view mirrors cause complex turbulentflow field in the wake of the mirrors, which have an effect on the surface pressuredistribution. So the shape of the mirrors is a key force in aerodynamic noisegenerating. Amounts of researches have been done on the aerodynamic characteristicsof the mirrors by wind tunnel tests and CFD simulations.Wind tunnel tests have been an indispensable section in the vehicle developmentcircle, providing technical support for vehicle design accurately. However, the testsneed high cost and long experimental period and can only be carried out with acomplete vehicle model or a real vehicle. In addition, detailed account of the wholeflow field is not accessible by tunnel tests. Compared with the traditional wind tunneltest, simulations based on CFD have a short experimental period and low cost as wellas the visualization of flow field. Thus, numerical simulation is commonly applied invehicle design process since the simulation method has these advantages.In this paper, research on the aerodynamic noise generated by the outside rearview mirrors were performed by experimental and numerical methods, which is alsopart of National Natural Science Foundation of China (No.51175214Research oninterior aerodynamic noise and control method based on flexible bionic outsidevehicle shapes). The aerodynamic noise tests were conducted in wind tunnellaboratory of Jilin University. The mirror was mounted on a table and microphoneswere attached in the downstream of the mirror on the table top to record the unsteadysurface pressure. The sound pressure levels at the measuring points were obtained byFFT. In the simulations the wind tunnel and the mirror were modeled for calculationof flow. LES was used as turbulence model in the calculation and static stress anddynamic stress was each applied to compare the effects on the results. According to the simulation results, dynamic stress as the subgrid-scale model was proved to be thebetter option for accurate simulation.The serration structures on the edge of the owl feathers were applied on themirror cover after the validation of the numerical method. It has been proved that theserration structures are main contributors to their silent flight. The flow fieldcharacteristics and surface pressure around the mirror were analysed for the originalmodel and modified model. The results suggest that the modification to the mirrorcontributes to noise reduction caused by the side view mirrors.Then the simulation of the complete car model was performed with two mirrormodels and the results have an agreement with the mirror model placed on the table,which validates the effect of the serration structures on noise reduction. Theconclusion of this paper has positive meaning to vehicles styling and NVH design.