Unsteady cooling air outflow and film coverage behaviors at blade leading-edge considering mainstream pulsation

Using large eddy simulation, this study examines the unsteady film cooling behavior at a blade leading edge under mainstream pulsation. Two film-hole designs are considered: a cylindrical hole (CH) and a trenched hole (TR). The instantaneous outflow of cooling air and the resulting film coverage are analyzed. A set of evaluation indicators is used to quantify the instability level, and the coherent structures in the flow field are also identified. The results show that: (1) In the downstream region, coherent structures appear in a band-like pattern, which creates a similarly banded region of high-unsteadiness in the film coverage. Both mainstream pulsation and the trench design reduce the number of these banded vortices but increase their spatial scale, thereby worsening the instability of film coverage. (2) Near the stagnation line, the high-unsteadiness region for the CH design takes an inverted triangular shape, while for the TR design it is mainly controlled by vortical structures inside the trench. (3) Statistical analysis indicates that under mainstream pulsation, the probability of extreme events ( P ( η = 0)) reaches 35.3 % for the CH design and 47.6 % for the TR design. (4) Mainstream pulsation significantly weakens the stability of film coverage, raising the surface-averaged standard deviation by 378.5 % for the CH design and 396.0 % for the TR design. (5) Mainstream pulsation also increases the total pressure loss coefficient by more than 500 %.