Large-eddy simulation of low-frequency unsteadiness in a turbulent shock-induced separation bubble

Abstract

The need for better understanding of the low-frequency unsteadiness observed in shock wave/turbulent boundary layer interactions has been driving research in this area for several decades. We present here a large-eddy simulation investigation of the interaction between an impinging oblique shock and a Mach 2.3 turbulent boundary layer. Contrary to past large-eddy simulation investigations on shock/turbulent boundary layer interactions, we have used an inflow technique which does not introduce any energetically-significant low frequencies into the domain, hence avoiding possible interference with the shock/boundary layer interaction system. The large-eddy simulation has been run for much longer times 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 excellent 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 large-eddy simulation data were analyzed and a phase change in the wall pressure fluctuations was found to coincide with the global-mode structure, leading to a possible driving mechanism for the observed low-frequency motions.Keywords shock boundary layer interaction · global mode · compressible turbulence · LES · low-frequency unsteadiness · separation bubble · digital filter · inflow turbulence PACS 47.40.Nm · 47.40.Ki · 47.27.ep

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