Transonic Linear Cascade Demonstration of Acoustic Flow Control on High Work and Lift Turbines

The study explores acoustic flow control in high-lift, high-work turbine blades (L3FHW and L4FHW) tested in a transonic linear cascade facility to tackle flows with open separations at low Reynolds numbers caused by high adverse pressure gradients. Acoustic excitation aims to focus on frequencies associated with the Kelvin-Helmholtz instability, which scales with the 3/2 power of the exit Mach number. Two different acoustic sources were utilized: a siren disk and a passive perforated tailboard, which functioned as a Helmholtz resonator. Experiments across various Mach numbers, supported by Schlieren imaging and static pressure measurements. Key findings demonstrate that siren disk excitation increased peak suction pressure by up to 60%, while reducing the angle of the separated shear layer by 10°. The tailboard excitation yielded a similar reduction of up to 11° in the shear layer angle, albeit with modest improvements in pressure recovery near the trailing edge. Tailboard excitation achieved a similar 11° reduction in shear layer angle, with modest improvements in pressure recovery near the trailing edge. Spectral analysis showed enhanced vortical coherence under excitation, with energy concentrating at target frequencies. Numerical simulations indicated up to 40% variation in peak suction pressure along the blade span due to end-wall vortices, suggesting secondary flows influencing the efficacy of flow control on midspan pressure distribution. Acoustic excitation demonstrated the ability to mitigate the adverse effects of end-wall vortices on pressure recovery. These findings highlight the potential of acoustic flow control to improve aerodynamic performance while underscoring the need to address secondary flow effects and integration challenges in advanced turbine designs.