Action Mechanism of Film Extraction on Channel Impingement Cooling for Blade Leading Edge Using Large Eddy Simulation

Abstract Various internal cooling techniques combined with external film cooling are applied to cool gas turbine blades, and the coolant extraction can cause variations in internal flow structures and cooling effectiveness. Effects of film extraction under different film hole diameters and coolant mass flow ratio on heat transfer and flow characteristics of channel impingement cooling are presented using large eddy simulation (LES) in this paper. The current work was undertaken based on turbine blade dimensions and turbine operating conditions. The results indicate that film extraction coupled with the curvature-induced instability dominates flow patterns and heat transfer in the channel impingement cooling structure with a film hole, especially in the bend region corresponding to the leading edge of turbine blades. Film coolant extraction can disrupt the streamwise counter-rotating flow circulation pair. The latter is caused by the curvature-induced instability and is also the major driver of multi-longitudinal vortices. Hole edge vortex generated by coolant bleed can amplify heat transfer at the leading edge, which is more significant as increasing the film hole diameters. Conversely, cooling effectiveness downstream of the cooling channel would decrease due to a reduction in cooling air. Film bleed flow would increase total pressure loss, while flow loss in the cooling channel decreases because of the weaken flow circulations and less coolant. This work provides an in-depth insight into the cooling performance of channel impingement cooling with film extraction, contributing to designing film cooling for turbine blades with multi-channel wall jet cooling.