On the Shock Boundary Layer Interaction in Transonic Compressor Blading

Abstract

Shock waves and their interaction with the boundary is a significant flow effect within transonic compressor blading. The main challenge here is the unsteady nature of this interaction effect because it imposes further requirements to maintain the structural integrity of the blading. Furthermore, it has been shown that the shock oscillations limit the working range of transonic blade profiles. Therefore, it is of great interest to mitigate these effects for the next generation of aero engine designs. In order to do this, it is mandatory to identify the mechanisms that originate the oscillation. Intensive experimental studies have already been carried out in the past using unsteady PIV, as well as Shadowgraphy, which have led to new insights into the nature behind the shock oscillation. However, the measurement insight into the flow is strongly limited and allows only an extract of the entire flow field. In order to get a deeper view, scale-resolving simulations have to be carried out. In addition to the experiments performed at DLRs Transonic Cascade Wind Tunnel, the flow through a transonic compressor cascade was simulated using a high-order accurate discontinuous Galerkin spectral element method with a finite-volume (FV) subcell shock capturing. The implicit LES scheme is applied for subgrid-scale dissipation, i.e. the dissipation is provided by the intercell flux. The content of the paper includes first a validation of the LES results based on the steady measurement data from the experiment in order to ensure the datasets are comparable. The comparison shows that the experimental operating point is almost exactly reproduced by the LES with respect to the mean inflow conditions and the resulting profile Mach number distribution. A time-frequency analysis is also shown, which was based on the evaluation of local probe data and on spectral decomposition of the simulation snapshots taken. Dominant frequencies of the shock movement and the vortex shedding of the transonic flow are extracted and used to analyze the unsteady flow behavior in a direct comparison with the experimental results. These analyses give a unique insight into the self-exciting mechanism of the shock oscillation and form the basis for the applicability of combined experimental and LES data set for a deeper analysis of the mechanism in future studies.