Abstract
An increase of turbine blade loading reduces the numbers of blade and stage. As a result, the downsizing and the weight reduction of gas turbines can be achieved. On the other hand, an increase of blade loading makes the secondary flow much stronger because of the steep pressure gradient across the blade-to-blade passage and deteriorates the turbine efficiency. In this study, the computations were performed for the flow in an ultra-highly loaded turbine cascade with high turning angle in order to clarify the effects of the incidence angle on the secondary flow and the loss generation. For the verification of the computed results, the experimental oil flow visualizations were also conducted on the blade surface and the endwall. Moreover, the measurements of blade surface static pressure were performed at midspan of the blade. The computed results showed good agreement with the experimental results. The influences of the incidence angle on the secondary flow structure, the total pressure loss, the secondary flow kinetic energy and the blade loading distribution were examined in detail. The positive incidences not only strengthened the horseshoe vortex and the passage vortex but also induced the newly formed vortex on the endwall, which was generated by the interaction of the reversed flow along the suction surface caused by the strong passage cross flow with the incoming boundary layer. Moreover, the newly formed vortex influenced the formation of the pressure side leg of horseshoe vortex.
