Nonlinear decay in turbine endwall film cooling induced by mainstream oscillation: High-frequency excitation effects on suction-side flow separation and suppression strategies

Thermal protection of gas turbine components under dynamic flow conditions is critically challenged by two intertwined mechanisms that govern film cooling performance degradation: intensified turbulence mixing at the mainstream–coolant interface and diminished coolant retention near the wall due to momentum redistribution. Large-eddy simulations were implemented to systematically elucidate the interdependent mechanism between mainstream oscillation and end wall crossflow in film cooling. It was revealed that high-frequency mainstream oscillations (>130 Hz) amplify turbulent kinetic energy at the interface by 4.5 times compared to low-frequency conditions, significantly disrupting coolant film stability. This enhanced mixing is attributed to the breakdown of coherent vortex structures. Concurrently, momentum redistribution under oscillatory flows shifts streamwise momentum to radial components, reducing coolant adhesion and driving migration toward the suction side—where temperature fluctuations surge by 32% due to flow separation and low-momentum zone expansion. These findings align with experimental observations of scaled expansion holes, which mitigate transverse flow interference and maintain uniform velocity distributions to improve near-wall coolant retention. This study establishes a dual-pathway framework for cooling performance decline, bridging flow physics (e.g., vortex dynamics) with engineering solutions (e.g., anti-kidney vortex designs), and provides actionable insights for optimizing cooling systems in pulsating environments.