Investigation of a Separated Boundary Layer and its Influence on Secondary Flow of a Transonic Turbine Profile

Abstract

Profile losses of the turbine blade and secondary flow losses are the main source of aerodynamic loss in a low pressure turbine. However, not much attention has been paid in the interaction between these two loss sources. This paper investigates the interaction mechanisms between a separated boundary layer on the suction side and the secondary flow in blade passages. The high speed cascade wind tunnel of the University of the Federal Armed Forces Germany has been used to achieve the required operation conditions, generating a flow separation on the suction side. The profile of this cascade has been chosen due to the flow separation behavior on the suction side of the blade at low Reynolds numbers. Different measurements techniques are conducted to further investigate the effects seen in CFD. The aim of this paper is to investigate the interaction phenomena between the secondary flow and a separation bubble at different Reynolds numbers. The development and change of the boundary layer in the axial and radial directions on the suction side of the turbine blade are presented and discussed. The results show discrepancies between the numerical prediction and the experimental data on the suction side of the blade rise as the effects of the secondary flow increase. Furthermore, the increasing influence of the radial pressure gradient of the secondary flow leads to a noticeable reduction in the length of the separation bubble close to the endwall region.