Situations where an incident shock wave impiges upon a boundary layer are common in the aeronautical and spatial industries. For instance, it can occur in the flow around supersonic aircrafts, in turbojets, supersonic air intakes or rocket nozzles. Under certain circumstances (High Mach number, large shock angle...), the interaction between an incident shock wave impinging a boundary layer may create an unsteady separation bubble. This bubble, as well as the subsequent reflected shock wave, are known to oscillate in a low-frequency streamwise motion that can spread over several tenth of the boundary layer thickness. This unsteadiness of the SWBLI subjects structures to oscillating loads that can lead to damages for the solid structure integrity. So, a carreful attention must be paid for this issue. The origin of those oscillations, however still unclear, has been related either to the shedding of vortices in the mixing layer downstream of the separation, or to the turbulent structures in the incoming boundary layer [Delery and Dussauge, 2009].

An in-house parallel (MPI) Finite-Volume DNS/LES solver, based on an original high order scheme including a shock capturing procedure (OSMP7), has been developed at LIMSI-CNRS [Daru and Tenaud, 2004]. The ability of this code to compute high Reynolds compressible (turbulent and shocked) flows has already been demonstrated in a previous work [Ben Hassan Saïdi et al., 2018]. This code is used to perform direct numerical simulations of the SWBLI in order to better understand the mechanisms leading to the unsteadiness of the SWBLI. We chose to perform SWBLI simulations supressing one of the two suspected mechanisms leading to the unsteadiness. As a first step, by simulating the interaction between a laminar boundary layer and an incident shock wave, we suppress the suspected influence of the large turbulent structures of the boundary layer on the SWBLI unsteadiness. The only remaining suspected cause of unsteadiness would be the dynamics of the separation bubble. The flow conditions are nearly similar to the test case of Degrez [Degrez et al., 1987] with a shock wave angle increased in order to strengthen the interaction and trigger the unsteadiness of the separation bubble. First results have shown that the location of the reattachment point of the recirculation bubble have an oscillatory motion. A strong intermittency of the shedding responsible for low-frequency reattachment shock oscillations have also been evidenced. Nevertheless, in this configuration, the separation point of the recirculation bubble has a fixed location along the flat plate. Consequently, even if the recirculation bubble have an unsteady dynamics, no unsteadiness of the whole SWBLI system occurs for this interaction with a laminar boundary layer.

These results tend to suggest the importance of the turbulent structures of the incoming boundary layer in the low frequency oscillations of the SWBLI system. In this context, the accurate simulation of a turbulent compressible incoming boudary layer is of great importance. A Synthetic Eddy Method [Jarrin et al., 2004] that we adapted to compressible flow, have been developed to achieve this objective without prohibitive additional computational costs. Comparisons between results obtained with the compressible Synthetic Eddy Method and reference direct numerical simulations of compressible turbulent boundary layer developing on a flate plate will be presented during the conference. The compressible Synthetic Eddy Method is used to perform direct numerical simulations of a SWTBLI (shock wave turbulent boundary layer interaction). Analyses of the SWTBLI dynamics and comparisons with the SWLBLI (shock wave laminar boundary layer interaction) will be presented at the conference. The comparison of the results obtained with and without incoming turbulent structures allows to better understand the mechanism leading to the unsteadiness of the whole SWBLI system.