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 [Formula: see text], 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.

The aerodynamic performances of the cascade can be improved using the filleted blade profile. The non-uniform distributions of the endwall film-cooling flow from the cylindrical coolant holes have prompted the investigations of cascade flow-field employing several variations of the cylindrical coolant hole geometry. While some variants of the cylindrical hole show potential of improved film-cooling effectiveness on the endwall, the aerodynamic performances of the cascade on the other hand suffer. This paper presents results from the measurements of the flow-field and air temperature along a cascade passage that employs filleted vanes and endwall film-cooling using a diffused shape of the cylindrical coolant holes. The experimental results are also presented in the same vane cascade with the endwall film-cooling using the regular cylindrical coolant holes and without the fillet at the vane endwall junction. The diffused coolant hole is a smooth geometric variation of diffused area of the cylindrical hole and diffuses the coolant flow smoothly along the hole axis. The objectives are to investigate the effects of the fillet and new diffused cylindrical hole on the cascade aerodynamic performances. The effects are illuminated through the interactions of the coolant streams with the mainstream. The measurements are obtained in a linear atmospheric cascade employing a two-dimensional vane profile and an inlet Reynolds number of 2.0E+06. The axis of the coolant holes are oriented at 30° to the endwall at inlet from the coolant plenum. The coolant holes are employed both at upstream and inside of the cascade passage. The fillet extends from the leading edge region to half-way of the vane profile. The time-averaged local velocities, total pressures, and air temperatures are measured at different pitchwise planes in the cascade for the different cases at the endwall. The density ratio of the coolant flow to mainstream is about 1.0 for the flow-field measurements and about 0.94 for the temperature measurements. The overall blowing ratio of the film-cooling flow varies between 1.0 and 2.8. The results of the yaw angle deviations of endwall region flow, total pressure loss coefficients, and non-dimensional temperatures are then presented to provide the effects of the fillet and film-cooling hole geometry. The results show the desirable performances of the local distributions and concentrations of the coolant streams, the low flow turning near endwall, and the reduction of total pressure losses are better when the diffused holes are employed without the presence of fillet. With the fillet and diffused cylindrical holes, the aforementioned aerodynamic performances are improved further compared to those for the regular cylindrical coolant holes.