The Influence of Rotor-Wakes on Boundary Layer Development in an Axial Compressor and its Numerical Prediction

This paper provides an analysis and discussion of the development of rotor wakes, and their influence on the boundary layer along a downstream axial compressor vane. Numerical investigations are carried out by means of unsteady RANS and Scale-Adaptive Simulations which apply the Shear Stress Transport turbulence model coupled to the γ-Reθ transition model. Numerical results are compared with the previously published and newly measured experimental data of a two-stage low-speed axial research compressor with IGV. In order to determine the differences between the numerical simulations and experimental data, space-time diagrams of wall shear stress and shape factor on the surface of the first vane are used together with upstream turbulence intensity. Special emphasis is put on differences in the wake development downstream of the blade, and their influence on the vane’s boundary layer development. It is shown, that there are still crucial limitations in the prediction of the wake development, especially the wake width and intensity. The badly-predicted wakes lead to an inaccurate prediction of the boundary layer development. A possibility to overcome the inaccurate prediction of the boundary layer development is proposed. The apparent advantage of the Scale-Adaptive Simulations, i.e allowing to resolve turbulent structures and large-scale unsteadiness, does not lead to a better prediction of transition processes. On the contrary, coupling the γ–Reθ transition model to Scale-Adaptive Simulations lead to further disadvantages.