Heat transfer coefficient augmentation for a shaped film cooling hole at a range of compound angles

Film cooling holes with shaped diffusers are used to efficiently deliver coolant to the surface of a gas turbine part to keep metal temperatures low. Reducing the heat flux into a component, relative to a case with no coolant injection, is the ultimate goal of film cooling. This reduction in heat flux is primarily achieved via a lower driving temperature at the wall for convection, represented by the adiabatic effectiveness. Another important consideration, however, is how the disturbance to the flowfield and thermal field caused by the injection of coolant augments the heat transfer coefficient. The present study examines the spatially resolved heat transfer coefficient augmentation, measured using a constant heat flux foil and infrared (IR) thermography, for a shaped film cooling hole at a range of compound angles. Results show that the heat transfer coefficient increases with the compound angle and the blowing ratio. Due to the unique asymmetric flowfield of a compound angle hole, a significant amount of augmentation occurs to the side of the film cooling jet, where the very little coolant is present. This causes local regions of increased heat flux, which is counter to the goal of film cooling.