Impact of Tailboard Configuration on Flow Periodicity in Transonic Low-Pressure Turbine Cascades

Abstract Future generations of fighter aircraft engines will require Low-Pressure Turbine (LPT) profiles able to operate efficiently under transonic flow conditions. This study, part of the NEUMANN project (“Novel Energy and Propulsion Systems for Air Dominance”), investigates the aerodynamic behavior of state-of-the-art transonic LPT profiles through experimental and numerical validation. A turbine linear cascade, developed using literature guidelines and RANS analyses, was tested in the C-3 blow-down high-speed wind tunnel at the von Karman Institute. The test section featured two different tailboards (TBs) configurations: one with a sudden step downstream the blades and another aligned tangentially to the cascade outlet. This allowed to assess the effects of the tailboard configuration on the flow pattern. The cascade was tested under conditions ranging from highly subsonic to supersonic, with Mach numbers between 0.8 and 1.2 and Reynolds numbers among 700,000 and 1.2 million. Flow periodicity, crucial for accurate flow analysis within the cascade passages, was obtained by adjusting tailboard inclinations and monitoring the outlet isentropic Mach number. Inlet and outlet flow conditions were investigated using aerodynamic and optical measurements techniques. RANS simulations, both steady and unsteady, were conducted on an infinite 2D cascade with periodic boundary conditions and on the full rig setup featuring step tailboard. The assessment of the best tailboard configuration was performed by analyzing the passage-to-passage variation, the deviation between the experimental and numerical blade loadings and Schlieren images. This comprehensive comparison allowed for an in-depth evaluation of the setup’s capability to accurately capture transonic flow phenomena in future-generation LPT airfoils, enhancing the understanding of finite-blade configurations in high-speed wind tunnels.