Flow fields and losses downstream of an ultra-highly loaded turbine cascade with bowed blades

Abstract

For the first time, a systematic experimental investigation on flow fields and losses of an ultra-highly loaded turbine cascade with bowed blades has been conducted. Flow patterns, secondary flow vortices and vectors, losses, and yaw angles at the downstream outlet have been analysed based on the measurements. The results show that the flow fields downstream of the cascade are characterized by a complicated vortex structure including passage vortices (PVs), trailing edge vortices (TVs), and corner vortices (CVs). The high-loss cores at the cascade outlet roughly correspond to the high-vorticity regions. A −20° bow angle gives the optimal aerodynamic performance under the conditions of this work, but the overall improvement is not significant. Appropriate negative blade bowing weakens the PVs and TVs and prevents the meeting and mixing of the PVs at the midspan, hence improving the flow fields and reducing the overall losses. However, negative blade bowing also increases the flow separation in corner regions, and enhances the CVs and the accumulation of low-energy air flow. This partially counteracts the beneficial effects, making the overall improvement not significant. The pitch-averaged yaw angle at the outlet of the cascade varies dramatically over the whole span. Negative blade bowing can improve the uniformity of the yaw angle distribution at the outlet. On the contrary, positive blade bowing degrades the aerodynamic performance of the cascade.