Roughness Investigations on In-Service High-Pressure Compressor Blades – Part II: Roughness Parameterization and CFD-Based Modelling of its Impact on Turbulent Flows

The two-part publication deals with roughness investigations on in-service high-pressure compressor (HPC) blades, both in terms of measurements and simulations. In this paper (Part II), first, stripe measurements of surface roughness coming from the suction side of the blades are conducted, using a highly accurate Alicona measuring device (see Part I for details of the measurement approach). Then, these roughness distributions are used to construct the walls of zero-pressure-gradient, fully turbulent channel flow simulations. Body-fitted unstructured grids of up to 80M nodes are generated, on which wall-resolved LES as well as RANS simulations with the k-ω SST turbulence model are performed. The CFD setup is first validated on a smooth channel reference case against LES and DNS data from the relevant literature. In addition, the impact of Reynolds number on several rough channel flow simulations is explored, using two different setups at Re_τ = 540 and Re_τ = 880. Finally, after an identification of the most important roughness parameters (given the relatively limited database at hand), a new roughness function model is proposed, which would allow the prediction of the flow over a rough surface without the need of geometrically resolving the roughness scales.