An experimental investigation on the aerodynamic performance and flowfield structure of a film-cooled turbine cascade

Experiments have been performed to study the aerodynamic performance and internal flows in a linear turbine cascade with air injection from various locations of the blade surface. Data were obtained by using pneumatic probe, static pressure taps and surface flow visualization techniques. The experimental results showed that the suction side injection would affect the development of the passage vortex significantly. The passage vortex was strengthened and pushed away from the injection surface, a triangular-shaped region uncovered by the injected air always existed on the suction surface due to the existence of the passage vortex. The passage vortex was weakened with air injection from pressure surface, which would cause a smaller amount of low momentum fluids to migrate into the corner region between suction surface and end wall. Although the scale and intensity of kidney-shaped vortices were different when air was injected from various positions, these vortices might always exist near the blade surface, mixing with mainflow in the flow passage and with wakes at the cascade exit while they moved downstream. The energy loss increased near the blade surface from which air was injected due mainly to the mixing process between mainflow and injected air, and to the formation of kidney-shaped vortices. In contrast to the pressure side injection, the changes of blade surface pressure distribution were more sensitive to the amount of injected air and the locations of injection holes for the suction side injection. In the great majority of cases, the surface pressure decreases owing to the existence of low-pressure zone downstream of the injection holes were more significant than the pressure increases caused by mainflow stagnation upstream of the holes.