A comparative study of varying incidence angle effects on a low-Reynolds-number compressor cascade based on experiments, low-fidelity and high-fidelity numerical simulations

Abstract

The ongoing trend in modern turbomachinery design towards higher bypass ratios and smaller core engines follows a locally reduced Reynolds number distribution in the compressor. While previous compressor blades were mostly designed for high Reynolds number operating points, the blade design specifically for a lower Reynolds number is becoming more important. However, these new operating points are characterised by large regions of flow separation and high levels of unsteadiness, where standard numerical design tools such as Reynolds-averaged Navier-Stokes (RANS) simulations typically exhibit high uncertainties. This can lead to incorrect predictions of the effects of varying incidence angles as shown in Hergt et al. (Low Reynolds Number Effects in Compressor Blade Design, IGTC, 2024). On the other hand, high-fidelity numerical tools such as large-eddy simulations (LES), which resolve most of the scales of the turbulent spectrum, are particularly suited to these operating points due to their relatively low computational requirements. In this paper, we assess the capabilities of low- and high-fidelity numerical tools to predict the effects of varying incidence angles for a linear compressor cascade at a Reynolds number of 150,000 and Mach number of 0.6 based on the inflow conditions. The comparison is supported by experiments carried out at the Transonic Cascade Wind Tunnel at the DLR in Cologne, which feature an incidence angle variation of plus/minus 5 degrees. The RANS simulations are performed with the finite volume branch of DLR's CFD solver TRACE. For the LES, the high-order discontinuous Galerkin solver of TRACE is used. Particular emphasis is set on the numerical setup to reproduce the experimental cascade, discussing the effects of spanwise domain size, axial velocity density ratio and inflow turbulence. The comparison of the effects of the angle of incidence provides insights into separation, transition and loss mechanisms.