Oblique Shock Impinging on a Turbulent Boundary Layer: Low-Frequency Mechanisms.

Abstract

The need for better understanding of the low-frequency unsteadiness observed in shock- wave turbulent boundary layer interactions (SBLI) has been driving SBLI research for several decades. We present here a Large-Eddy Simulation (LES) investigation of the in- teraction between an impinging oblique shock and a turbulent boundary layer under the same flow conditions as in the experiments performed at the Institut Universitaire des Systemes Thermiques Industriels in Marseille (France). 1,2 Contrary to past LES inves- tigations on SBLI, we have used a new inflow technique which does not introduce any energetically-significant low frequencies into the domain, hence avoiding possible interfer- ence with the SBLI system. We have run the LES over much longer time series than previous computational studies making a Fourier analysis of the low-frequency possible. The broadband and energetic low-frequency component found in the interaction is in ex- cellent agreement with the experimental findings. Furthermore, a linear stability analysis of the mean flow was performed and a stationary unstable global mode was found. The long-run LES data were analyzed and found to coincide with the global mode structure, leading to a possible mechanism for the observed low-frequency motions.