Analysis of low-frequency characteristics in shock wave–turbulent boundary layer interaction through pressure fluctuation decomposition

This study employs direct numerical simulation to investigate the low-frequency wall pressure fluctuations in an incident shock-induced shock wave/turbulent boundary layer interaction (SBLI) at a freestream Mach number of 2.25 and an incident shock angle of 33.2°. By decomposing pressure fluctuations into linear, nonlinear, viscous, and harmonic components based on the governing equation, we demonstrate distinct scale-dependent behaviors. The fluctuations related to small-scale structures are dominated by the nonlinear component, which are of certain significance only in the free shear layer, while those associated with large-scale structures are mainly contributed by the linear component; viscous and harmonic effects are negligible. Pre-multiplied spectral analysis reveals that low-frequency characteristics, only presented in the intermittent region, originates primarily from the linear component, highlighting the role of flow distortion and compressibility effects. In contrast, the nonlinear component contributes only to higher frequencies. These findings provide new insights into low-frequency dynamics in incident shock-induced SBLI.