High-Fidelity Transonic Annular Turbine Rotor Measurements in the Stationary Frame

Abstract This paper presents the first comprehensive experimental campaign using a rainbow annular cascade of high-pressure turbine rotor airfoils using the new AMBRA stationary-frame methodology, which reproduces rotor-relative inflow conditions in a non-rotating annulus. A flow-conditioning gauze imposes prescribed radial and circumferential distributions of total pressure and whirl angle, enabling controlled testing of turbine geometries under transonic inflow conditions at exit Mach numbers near 0.85 and 1.00. Operating in a stationary configuration allows use of high-resolution instrumentation—such as dense blade-surface pressure taps, multi-rake traverses, and detailed flow-angle measurements—typically achievable only in low-speed linear cascades, but applied here to realistic transonic turbine environments where rotating rigs offer limited diagnostic access. Two turbine geometries were investigated over Reynolds numbers from approximately 300,000 to 1,000,000. The experimental suite included continuous circumferential traverses of Kiel and five-hole probes, with endwall and blade-surface static pressure measurements, and oil-flow visualizations. These complementary diagnostics enabled detailed characterization of passage vortices, shock locations, and loading evolution, as well as computation of area-averaged loss coefficients for performance comparison. The results show clear, repeatable differences between geometries, with loss distributions and flow-field features lying well outside the uncertainty bounds. By combining realistic annular inflow with dense spatial measurements, this approach bridges the gap between linear cascades and rotating rigs, offering a powerful framework for systematic evaluation of next-generation transonic turbine designs and secondary flows at TRL 3-4.