Cooling effectiveness of shaped film holes for leading edge

An experimental investigation has been carried out to improve the film cooling performance at the leading edge of a gas turbine vane. The standard cylindrical holes, located on the stagnation line, are modified with two expansion levels at the hole exit, 2d and 4d. A two-dimensional cascade has been employed to measure the cooling effectiveness of the two expansion levels and the standard hole using the transient Thermochromatic Liquid Crystal technique. The air is injected at 90o and 60o inclination angle relative to the vane surface with four blowing ratios ranging from 1 to 2 at a 0.9 density ratio. The Mach number and the Reynolds number of the main stream based on the cascade exit velocity and the axial chord are 0.23 and 1.4E5, respectively. The detailed local cooling effectiveness downstream the film holes over both the pressure side and the suction side are presented in addition to the lateral-averaged cooling effectiveness. The proposed expansion enhances the coolant distribution over the leading edge, particularly toward the suction side. The effectiveness increases toward the pressure side as well, yielding uniform thermal stresses around the stagnation line. The cooling effectiveness improved with increasing blowing ratio due to the jet lift-off reduction, hence higher cooling capacity is provided.

► An experimental investigation was performed to evaluate the smooth expansion hole on the leading edge of a vane.
► Two expansion levels were investigated in addition to the standard cylindrical hole at two inclination angles.
► The smooth expansion exit shows higher effectiveness when supplied with the same coolant amount.
► Increasing the blowing ratio with the proposed expansion improves the cooling effectiveness.