Acoustic noise generation in a compressible turbulent cylindrical boundary layer

Spatial direct numerical simulations are performed to study the development of turbulent structures and the associated sound emission in a compressible boundary layer, in order to compare with corresponding high-speed train model experiments conducted in a moving model facility, where the free stream velocity is 500km/h (corresponding Mach number is 0.41). In the simulation, finite difference upwind-biased compact schemes (spectral-like resolution) are employed. Boundary conditions based on characteristic analysis for the Navier-Stokes equations are used so that acoustic waves are not reflected back into the domain. Disturbances of compressible isotropic turbulence are superimposed on the laminar profile at the inlet boundary layer in the computational box. The Reynolds number based on the displacement thickness at the inlet is 1640, which corresponds the measurement of the boundary layer undergoing transition. Simulation results present the complex development of the hairpin vortices leading to turbulent boundary layer structures and the associated sound generation. The numerical aerodynamic noise frequency range and the attenuation of sound are in good agreement with the experimental results.