Investigation on noise from shock/isotropic turbulence interaction using direct numerical simulation

Direct numerical simulation of shock/isotropic turbulence interaction combining Lighthill acoustic analogy is conducted to study the influence of shock/turbulence interaction (STI) on the turbulence noise in this paper, for the first time. The upstream Mach number and upstream turbulent Mach number for STI simulation are 1.29 and 0.05 respectively. Based on the numerical simulation results, Power Spectral Density in the low frequency band is slightly increased under STI and the value in the high frequency band is obviously increased. Therefore, the acoustic intensity is amplified by STI. By analyzing the turbulent flowfield and the acoustic field, it is found that the isotropic upstream turbulence becoming axisymmetric turbulence under the one-dimensional compression of the normal shock wave. By decomposing the acoustic pressure into six parts according to different noise sources, the primary noise sources for the observation points in this paper are identified. The primary sources are constituted by the normal stresses in the transverse directions. Additionally, the turbulence intensity is weak in this paper, resulting in the primary noise sources being simplified as the production of density and second order time derivative of the normal stress. The mechanisms of noise variation under STI can be divided into two parts. First, the compression effect of shock wave increases the downstream density. Second, STI increases the turbulent kinetic energy spectrum over the entire wavenumber range.