Analysis And Application Research On Aerodynamic Noise Prediction Method For Engine Intake Manifold

With the amount of domestic vehicles increasing and the demand for noise pollution control becoming more and more intense,governments among the world have imposed mandatory restrictions on vehicle noise,so do our government.In addition,the mandatory restrictions will be further stricter in the future.Due to that engine is one of the main noise sources of the vehicle,it is necessary to consider low noise requirements at the design stage of the engine.Especially the intake noise occupies a large proportion in the total noise,thus we need further research on aerodynamic noise for prediction and reduction of intake noise at the design stage.Firstly,some method researches of aerodynamic noise in the intake manifold is studied.The influence of certain parameters on the accuracy of the calculation is analyzed based on the Computational Fluid Dynamics theory,aero-acoustics theory and Numerical Simulation methods.By using the hybrid calculation method,the aerodynamic noise of intake flow is predicted with Acoustic FEM based on the CFD results.Secondly,develop an aerodynamic noise simulation method for intake manifold based on transient boundary conditions so that the prediction accuracy of the aerodynamic noise improves by accurately simulating the flow in the intake manifold.The transient boundary parameters that needed in the flow field calculation are obtained from the one-dimensional thermodynamic simulation,and the one-dimensional model is calibrated by the test data to guarantee the accuracy of the velocity and pressure boundaries.In CFD simulation,Large-Eddy Simulation with Smagorinsky subgrid scale model which has additional damping equation,and Detached-Eddy Simulation with Improved Delayed-DES model are respectively used for more precise prediction.Then,study the motion of the flow filed by LES method and the result shows the motion state of airflow during the intake process visually.A large number of vortices occur because of the sectional area's sudden change and the tube curvature.The aerodynamic noise is then produced with the unceasing development of these eddies.We can also find that changes of airflow velocity in manifold cause the pressure fluctuation of the manifold surface.Then,compare the CFD results of LES method and DES method.It can be found that the distributions of surface pressure,velocity magnitude and velocity gradient are all very close,so are the position and strength of eddies.This means that the accuracy of the DES method is similar with that of the LES method,meanwhile its calculation time reduces by 13% than that of the LES method.The Sound Pressure Level(SPL)spectrums are obtained after the frequency domain conversion and acoustic response calculation.The frequency domain conversion and acoustic response calculation are based on the surface pressure fluctuation results calculated by the LES and the DES method respectively.Compare these two spectrums,it is found that these two spectral lines almost coincide and only few peaks have differences,indicating that the flow results of two algorithms can get closed SPL results.Then,the accuracy of simulation method is verified by NVH test,and the application potential of DES method in the aerodynamic noise prediction is also confirmed.Two kinds of peaks in the aerodynamic noise can be classified by the comparison between the simulation results and the pressure boundary spectrum so that different methods can be used to decrease the noise respectively.Finally,the prediction method of aerodynamic noise developed is applied to the intake manifold design of the engine,in order to predict its intake noise and analyze the sound field results,providing the basis for optimization and improvement of the intake system.