Abstract
To overcome the disadvantages of cylindrical holes in film cooling, complex geometries of the fan-shaped diffused holes are employed in cascade investigations. The present experiment employs a new design of a diffused hole for film cooling that is formed by diffusing a cylindrical hole smoothly and only in the forward direction. The aerothermal performances in a linear vane cascade are compared between an array of simple cylindrical holes and an array of diffused-cylindrical holes by employing them in the cascade upstream endwall. The objectives are to increase the aerothermal performance of the cylindrical holes in the gas-turbine passage film cooling. The measurements of the temperature, velocity, flow angle, and total-pressure losses are obtained at the inlet Reynolds number of 2.0E+05, as well as the coolant-to-mainstream density ratio of 1.0 and temperature ratios between 0.94 and 1.0. Four inlet blowing ratios of film-cooling flow are tested. The results show less coolant migration into the boundary layer and passage vortex for the diffused holes than for the cylindrical holes. The passage vortex becomes weaker, and the overall total-pressure losses at the passage exit are lower for the diffused holes. The local and average adiabatic film-cooling effectivenesses along the endwall are always higher for the diffused holes.