Measurements in a Turbine Cascade Over a Contoured Endwall: Discrete Hole Injection of Bleed Flow

Thermal and flow field measurements taken within a cascade passage are presented. The cascade has two passages between three airfoils and two endwalls, one flat and one contoured. Measurements were done on and near the contoured endwall. The main objective is to document the effectiveness of cooling the contoured endwall with bleed flow that emerges through two rows of staggered, discrete holes on the contoured endwall, upstream of the airfoils. Similar studies have been performed in our lab with bleed flow emerging from slots upstream of the same contoured endwall. Both those and the present studies are with high free stream turbulence intensity, TI ∼ 9%, of the approach flow. This is characteristic of the approach flow to first stage vanes in most operating engines. In the experiments, the bleed flow is heated slightly above the main stream flow and downstream temperature fields are documented. Three bleed flow rates are tested. It is shown that at a lower flow rate (1.5% of the core flow) the cascade endwall cross-flow carries coolant towards the suction side. However, as the coolant rate is increased, the coolant attains sufficient momentum that no suction-side coolant migration is seen. Velocity measurements taken with triple-sensor, hot-wire anemometry document migration of the bleed flow by way of showing regions of stronger shear, and help describe mixing of the passage flow with the bleed flow. At higher coolant flow rates, strong blockage and mixing effects become evident.