Controlling the secondary flow in a turbine cascade by three-dimensional airfoil design and endwall contouring

A highly loaded turbine cascade has been redesigned with the objective to r educe the secondary flow by applying endwall contouring and three-dimension al 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 thr ee-dimensional design environment, a systematic study has been carried out regarding several features of the endwall pressure distribution and their i nfluence on the secondary flow. Two optimized configurations have been inve stigated in a high-speed cascade wind tunnel. The flow field traverses show ed improvements concerning the radial extent of the secondary pow and a dec rease in secondary loss of 26 percent. Unfortunately this reduction was cou nterbalanced by increased profile losses and higher inlet losses due to inc reased blockage. The striking feature of the cascade with endwall contourin g and three-dimensional airfoil design was a significant reduction of the e xit flow angle deviations connected with the secondary flow. The prediction s obtained by the three dimensional Navier-Stokes solver TRACE_S showed a r emarkable agreement with the experimental results.