Unsteadiness in the Secondary Flows of a High-Speed Low-Pressure Turbine Cascade With Unsteady Wakes and Purge Flow

This work investigates the unsteady interactions between incoming wakes and purge flow in a high-speed low-pressure turbine cascade tested under engine-representative conditions. Experiments were conducted in a linear cascade at outlet Mach and Reynolds numbers of 0.90 and 70,000, respectively. Unsteady wakes characterized by a reduced frequency of 0.95 are generated by cylindrical bars. Purge flow was injected at varying mass flow rates through a cavity slot to study its effect on the modulation of secondary flows. Phase-averaged measurements using a fast-response pressure probe operated in a virtual mode mapped the unsteady development of secondary flows regarding energy loss, turbulence intensity, and flow angles at the outlet. Results highlight a significant strengthening of secondary flow structures when introducing purge flow, in contrast to the weaker passage vortex observed without the cavity slot. The passage vortex was periodically suppressed in the absence of purge, while purge flow enhanced the turbulence intensity and the extent of loss fluctuations in the secondary flow region. This study provides insights into secondary flow modulation and the complex interactions between purge flow and unsteady wakes.