Reduction of aerodynamic noise from a train car gap

To reduce aerodynamic noise from a train car gap—a major noise source of high-speed trains—we performed experimental and numerical investigations. Aerodynamic noise and the boundary layer that approaches the gap were measured using a scaled train model in a low-noise wind tunnel. We found that the aerodynamic noise has a broadband frequency and is radiated mainly from the downstream edge of the car gap where eddies collide. We also found that the boundary layer that approaches the gap is turbulent. To determine the unsteady flow field around the car gap, we performed a numerical simulation by using a Large Eddy Simulation (LES) with dynamic Smagorinsky model. The turbulent boundary layer that approaches the gap was also simulated. The magnitude of the pressure fluctuations is high at the downstream edge of the gap where eddies collide and is the main cause of aerodynamic noise. For a more detailed analysis, we performed wind tunnel tests using simplified cavity element models. We found that the shape of the gap edges greatly affects the aerodynamic noise and that by rounding the downstream edge, noise can be reduced.