Development of a novel film cooling hole geometry

This thesis presents the design, development and testing of a new film cooling hole geometry, the converging slot-hole or console. Both the thermal and aerodynamic performance were measured, using the adiabatic effectiveness and heat transfer coefficient, and aerodynamic loss respectively, to quantify performance. Comparative measurements were made, by testing conventional film cooling hole shapes in parallel with the console experiments. The CFD code, Fluent, was used to predict the performance of the initial design concept before it was manufactured. Initial performance measurements in incompressible flow were performed in a low speed wind tunnel at an engine representative Reynolds number based on mainstream flow and hole diameter. For these experiments, the coolant to mainstream density ratio was approximately unity, and the cooling performance was measured over a flat plate. The console was tested in parallel with cylindrical holes, a slot and fan-shaped holes, all of which had equal throat area per unit width. The heat transfer performance was measured at steady state using thermochromic liquid crystals sprayed onto a flat plate heater. The aerodynamic performance of the holes was measured by traversing the boundary layer 50 cylindrical hole diameters downstream of the injection location with a pitot probe. Engine representative measurements of the console performance were made in a transonic annular cascade that simulates the three-dimensional flow in the gas turbine. The Reynolds and Mach numbers were representative of engine conditions, and the coolant flow was made aerodynamically and thermodynamically similar to engine conditions by matching both the momentum flux and density ratios. This was achieved by using a heavy foreign gas with the composition of 30.2% SF6 and 69.8% Ar by weight, which simulates the coolant to mainstream density ratio of 1.78, and has a ratio of specific heats of 1.4. The performance of a nozzle guide vane with rows of fan-shaped holes was compared with an NGV with a film cooling configuration designed with rows of consoles replacing rows of fan-shaped holes. The heat transfer performance was measured using a modified step change transient liquid crystal technique. The aerodynamic performance was measured using a four hole probe traverse downstream of the NGV. The heat transfer performance of the console was found to be similar to or slightly lower than the performance of fan-shaped holes. The most significant benefit of the console was found to be the aerodynamic performance, with a loss due to film cooling of only 20% of the loss due to film cooling of the rows of fan-shaped holes measured at engine representative conditions.