Entropy generation rate and proper orthogonal decomposition analysis for unsteady flow and losses of turbine vane cutback

Trailing edge pressure-side cutback film cooling is a crucial technique to enhance the thermal protection of advanced turbine vanes. However, unsteady cutback film cooling significantly impacts turbine aerodynamic losses and cooling design. In this study, a new dual-passages trailing edge cutback is investigated by detached eddy simulation. Entropy generation rates and proper orthogonal decomposition are utilized to identify unsteady flow characteristics and specific loss intensities. The results indicate that film cooling efficiency is essentially consistent between single- and dual-passages cutbacks, with temperature deviation below 0.5 %. The variation in the thermal boundary layer and turbulent heat flux is closely related to the blowing ratio. Moreover, local and total entropy generation rates are employed to quantify the unsteady loss. Notably, the viscous entropy generation rate is significantly lower than the thermal entropy generation rate. Specifically, the instantaneous thermal entropy generation rate contributes over 50 % to the overall loss. This observation highlights the impact of irreversible heat transfer resulting from the mixing of the swirling coolant jet and the mainstream on unsteady losses in the trailing edge. Furthermore, the interaction between mainstream and coolant generates turbulent shedding vortices. Proper orthogonal decomposition practice accurately identifies wake shedding vortex pairs (f = 4072 Hz) and Kelvin-Helmholtz vortices (f = 5222 Hz). This study provides new analysis strategies for turbine cooling design considering unsteady film cooling and loss characteristics.