Investigation of the Effects of an Upstream Cavity on the Secondary Flow in Transonic Turbine Blade Passages with Endwall Contouring

The investigation documented here aims to contribute to the understanding of secondary flows in modern high-pressure (HP) turbine blade passages. More specifically, it aims to improve the understanding of vortical structures near the endwall with respect to the presence of an upstream cavity that approximates the gap present in actual engines between the rotor and stator of an HP turbine. Further, it aims to assess the viability of using non-axisymmetric endwall contouring to reduce endwall losses, including those generated by the presence of an upstream cavity, using a modern airfoil, at HP turbine representative speeds and at off-design Mach numbers. To attempt to achieve this, a combination of flow measurement, flow visualization, and computational fluid dynamics (CFD) with linear turbine cascades was used. The test matrix consisted of three cases all with one common blade cascade geometry (SL2P). SL2P was combined with one of three endwalls: a baseline flat endwall, a flat endwall with a cavity incorporated upstream of the blade row, and a contoured endwall with the same upstream cavity geometry. A combination of pressure probes, pressure taps, and flow visualization were used to collect quantitative and qualitative data in a blow-down type wind tunnel. Complementary CFD studies were also carried out using the commercial CFD code ANSYS CFX.