Controlling the Secondary Flow in a Turbine Cascade by Three-Dimensional Airfoil Design and Endwall Contouring

Abstract

A highly loaded turbine cascade has been redesigned with the objective to reduce the secondary flow by applying endwall contouring and three-dimensional airfoil design in the endwall regions. The overall loading and the axial area ratio of the cascade have been kept constant. With the tools of a three-dimensional design environment, a systematic study has been carried out regarding several features of the endwall pressure distribution and their influence on the secondary flow. Two optimized configurations have been investigated in a high-speed cascade wind tunnel. The flow field traverses showed improvements concerning the radial extent of the secondary flow and a decrease in secondary loss of 26 percent. Unfortunately this reduction was counterbalanced by increased profile losses and higher inlet losses due to increased blockage. The striking feature of the cascade with endwall contouring and three-dimensional airfoil design was a significant reduction of the exit flow angle deviations connected with the secondary flow. The predictions obtained by the three-dimensional Navier–Stokes solver TRACE_S showed a remarkable agreement with the experimental results.