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

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 article. 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 counterrotating flow circulation pair. The latter is caused by the curvature-induced instability and is also the major driver of multilongitudinal vortices. The hole edge vortex generated by coolant bleed amplifies heat transfer at the leading edge, and the effect is more significant as the film hole diameter increases. Conversely, heat transfer coefficient downstream of the cooling channel decreases due to a reduction in cooling air. The increasing film bleed flow increases overall total pressure loss, while flow loss in the cooling channel decreases because of the weakened flow circulations and reduced coolant mass flow. 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 multichannel wall jet cooling.