Reduction of endwall secondary flow losses with leading-edge fillet in a highly loaded low-pressure turbine

Abstract

A detailed experimental and numerical investigation of the effect of leading-edge fillet on the endwall secondary flow was performed in a highly loaded low-pressure turbine cascade. The objective is to gain further understanding on the reduction mechanism of endwall secondary flow losses by leading-edge fillet. The results suggest that the numerical results offer a reliable prediction for the endwall secondary flow structure together with suction surface separation bubble. A pressure-side corner separation vortex is found in the front part of pressure surface/endwall junction, where an inverse flow goes upward and over the leading edge to suction side of the same blade. This inverse flow also takes part in the interaction between endwall secondary flow and separation bubble. However, the leading-edge fillet can fill the region of corner separation vortex, and the inverse flow is eliminated. Combined with the reduction of cross-pressure gradient achieved by this fillet, the loss coefficient and flow angle deviation at exit plane are decreased. Besides, the leading-edge fillet will reduce the intensity of leading-edge horseshoe vortex and thus decrease the loss of passage vortex and shed vortex. It is these three aspects introduced by leading-edge fillet that achieves an effective reduction of the endwall secondary loss in turbine.