The Numerical Simulation Of Hight-Speed Train’s Aerodynamic Noise And Its Influence

As the high-speed railway continues to develop, the speed of the trains keeps on augmenting. Many problems previously neglected due to the relatively low speed have become critical and affect the further development of the high-speed railway. According to previous studies, the aerodynamic noise of the high-speed train is determined by the translational velocity u, its level is proportional to six to eighth power of the velocity u. Therefore, the aerodynamic noise will improve significantly as the speed goes up. When the high-speed train runs at300km/h, the aerodynamic noise will out-weigh the noise caused by the wheel and rail, thus becoming the principal noise source. In this paper, based on the Lighthill’s acoustic analogy theory, the author utilizes the Computational Fluid Dynamics (CFD) combined with the Boundary Element Method (BEM) to simulate the distribution of the far-field external aerodynamic noise of a CRH2high-speed train at the speed of300km/h and the noise propagation characteristics when a noise barrier is considered.The main works of the author are listed as follows:1) Three dimensional numerical analysis of the aerodynamic field around the vehicle.In the first place, the numerical simulation model of a CRH2high-speed train is established. Then the Large Eddy Simulation (LES) is executed to calculate the transient-state aerodynamic field of the vehicle at300km/h. The analysis shows that negative pressure is generated in the flow separation zone attached to the train’s surface due to the strip of the boundary layer. The striped flow forms small bubbles and further evolves into turbulence that possesses strong dynamic pressure. The turbulence and the dynamic pressure are also very strong near the bogies of the vehicle.2) Numerical analysis of the aerodynamic dipole sources distribution at the vehicle’s surface.Based on the Lighthill’s acoustic analogy theory, the previously calculated fluctuating pressures at the surface of the high-speed train are transformed into the Boundary Element Model as the boundary condition via the finite difference method. The simulation illustrates that the distribution of the acoustic dipole sources shows great coincidence with the turbulence zone.3) Study of the radiation acoustic field based on the dipole acoustic sources around the vehicle’s contour.By imposing the dipole acoustic sources at the vehicle’s surface as the boundary condition, the author solves the Helmholtz equation using the Direct Boundary Element Method (DBEM), which allow us obtain the external aerodynamic noise field of the high-speed railway. Then various discussions on the distribution of the noise field are investigated in detail.4) Numerical study of the noise barrier’s influences on the aerodynamic noise field caused by the dipole acoustic sources of the high-speed railway.The influences of the noise barrier on the acoustic radiation characteristics are discussed first. Then by varying the height of the noise barrier, the author reveals its influences on the aerodynamic noise along the railway lines.