Meshless Prediction Method Of Aerodynamic Noise At Inner-coach Space Of High-speed Train

The phenomenon of fluid induced aerodynamic noise has been noticed for a long time.And a lot of research work has been done.In recent years,the cavity aerodynamic noise,as a common noise source in the high-speed train noise,has attracted people's attention,such as the noise from the connection of the carriage.Reducing the aerodynamic noise of the cavity can improve people's ride comfort and reduce the noise pollution of the high-speed train to the surrounding environment,which has important practical value and academic significance.In this study,a mesh free method for predicting the aerodynamic noise of the cavity is developed.Firstly,the discrete vortex method is used to capture the flow details at the opening of the cavity flow field.And the key factors such as vorticity,position and velocity of the point vortex are obtained.The frequency of falling off is calculated under different inflow velocity.It is found that the frequency of shedding increases linearly with the increase of inflow velocity at low Mach number.The results are in good agreement with Rossiter's semi empirical formula.Then,the direct point vortex is used as the sound source to solve the cavity sound field using the vortex theory.Two dimensional time domain boundary element method is used to simulate the reflection effect of the cavity wall on the sound field and calculate the sound field distribution of the cavity.By analyzing the data of different monitoring points,the directivity of cavity sound field is obtained,which shows the characteristics of dipole source.In order to verify the accuracy of the meshless method,the commercial software FLUENT was used to simulate the aerodynamic noise of the cavity.First,the LES model is used to calculate the flow field of the cavity.Both methods capture the process of the vortex cluster formed by the shedding vortex from appearance to dissipation.After the flow field is stable,the noise module is turned on.And the acoustic field of the cavity is simulated by FW-H acoustic analogy method.Through the data processing,the directivity of the sound field obtained is consistent with the meshless method.The spectrum of the same monitoring point is analyzed.The results of the two methods are in good agreement,especially in the low frequency range.