Visualization Techniques On Exterior Acoustic Field Of Vehicle Tailpipe

In order to meet the statutory and regulatory requirements,and improve the expe-rience of driving and riding as well,auto manufacturers have paid more attention on vehicle's NVH performance.As we known,the exhaust noise has a high contribution rate to the interior noise and pass-by noise,while the acoustic field and flow field are deep inter-coupling and the sounding mechanism is complicated in exhaust noise case,therefore the simulation and experiment about exhaust noise are difficult in normal condi-tions.To promote the match design of exhaust system,there are serverl studies on exhause noise in this dissertation,such as the 3D simulation of jet flow noise in time domain,the sound sources localization in 3D outer sound field and building a platform of the exhaust simulator.A hybird 3D simulation method has applied to the outer acoustic field of exhause,which could describle the impact of 3D flow field to acoustic field.This hybird method has a high association precision with the acceptable amount of computations,thus is practicable in engineering application.Three-deimensional unsteady flow field of exhaust is studied by the large eddy simulation(LES)method,then the aeroacoustic sources are extracted from the transient flow field through Light-hill acoustic analogy(AA).The simulation result shows that the distribution of acoustic sources intensity is closely related to the exhaust flow field,and the radiation sound has a clear directivity.The validity of this numerical method is demonstrated by the experiments.In this case the methodology of sources localization is based on the time difference of arrival(TDOA),while the aeroacoustic sources of the exhaust distribute in 3D space.The formula for the location error is derived which including the precision of time-difference estimation and the arrangement of microphone array.The mapping relationship between the time-difference value and the spatial position of source has been studied,and then a nonlinear estimation algorithm of time-difference is presented which makes the localization accuracy is less sensitive to the position of source.For the purpose of improving the accuracy of source localization,two subarrays are used to locate the sound source,then the intersection of two error ellipse's major axes which are obtained from the covariance matrix of the observations is regard as the optimized location result.The experiments show that the fore mentioned method is effective.To solve the localization ambiguity problem in case of multiple sound source,an approach based on redundancy TDOA is proposed to identify and match the TDOA pair,which can effectively eliminate the fake location points.On the other hand,a kind of coordinate transform method is employed in improving the spatial resolution of sources localization.The Cartesian coordinates of all observations are mapped into a sphere coordinate system with the origin at the center of microphone array,then the cluster analysis for sources positions based on azimuth and elevation.A bench of exhaust simulator has been designed and built,that consisits of the air supply segment,the sound generation segment,the air flowmeter and the control system.The acoustic parameters and backpressure of exhaust can be measured on that bench while the mass flow of air is quantitatively controlled.The outer acoustic field of exhaust has been studied,the sound sources at different frequency bands are positioned in 3D space.