| Promoted by the national policy and technological progress,automobile enterprises in China paid more attention on energy conservation and environmental protection.However,cabin comfort is definitely an important indicator which could help a lot on driver’s feelings and on driving safety.Automotive aerodynamic noise is an important indicator of cabin comfort,and a good noise level will significantly enhance the cabin comfort experience of passengers.At high speeds,aerodynamic noise could become the largest noise source.At present,the mainstream automobile enterprises are increasingly aware of the importance of automotive aerodynamic noise.Although their aerodynamic noise research started late,they tried their best to study.The enterprises in foreign countries have a more in-depth study about aerodynamic noise,both in computational fluid dynamics(CFD)simulation and acoustic wind tunnel noise experiment.So the domestic automobile factories paid much money on technology development to make the aerodynamic noise characteristics better.As a larger convex part of automobile in the outer flow field,rearview mirror occupies the side window which is an important position for occupant comfort.It also has a relatively large effect on aerodynamic noise.This study aims to research the unsteady flow through the analysis of its vortex structure,to explore the aerodynamic noise simulation method through the simulation of monitor noise and the comparison with the experiment.What’s more,we can reduce the aerodynamic noise in the wake field of the rearview mirror.In this paper,the CFD simulation and particle image velocimetry(PIV)techniques are used to analysis the wake flow of side mirror.The PIV experiment was carried out in the automotive wind tunnel laboratory,the side mirror was mounted on the test bench.The unsteady flow field could be captured and Tecplot software was used to process the images.In the CFD simulation,we choose the RANS equation to simulate the steady-state flow field,by comparing the simulation result with PIV experiment,there are the same flow field that could be find.Through the analysis of time-averaged streamline pattern and vorticity contour,we can find that there is obviously a Karman Vortex Street in the Z section plane wake flow field of the mirror.The unsteady wake flow field of side mirror is so complicated that we’d better research the instantaneous flow by using PIV experiment and LES simulation.When talk about the aerodynamic noise analysis,we use acoustic wind tunnel tests to help improve the numerical simulation results.In the acoustic wind tunnel test,the sound pressure level curves,A weighted sound Pressure level curves,and total noise values from monitoring points are the main values that we concerned.In the simulation of aerodynamic noise,we make a mesh refinement in the wake field of side mirror,and set the first layer of the boundary layers to 0.07 mm,we choose the large eddy simulation to simulate the noise.The sound pressure level curves we get from simulation and experiment results could be compared at different frequencies,it helps a lot to understand the noise level of different monitoring points in the wake flow of side mirror.Finally,three schemes are put out to reduce the noise of side mirror.There are three schemes: stretch the windward side,the tail extension of side mirror,add strip groove on the tail of side mirror.All the schemes have achieved a certain degree of noise reduction,the vortex structure was reduced and the noise level decreased 1-3 dB. |
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