Experimental investigation and numerical analysis on effects of swirling coolant on flow characteristics and film cooling performance

Modern gas turbines use combined internal and external cooling methods to achieve higher cooling effectiveness. The internal cooling methods, like internal serpentine channel cooling and impingement cooling, will introduce swirl to the coolant of film cooling. In this paper, film cooling effectiveness of one row and two rows of holes with and without swirling coolant was measured using pressure sensitive paint (PSP). Numerical simulations were performed to analyze the flow structures. Results show that swirl in coolant enhances film cooling effectiveness for one row of holes when the density ratio is low or blowing ratio is high. When the blowing ratios are 1.0 and 1.5, the improvements of averaged film cooling effectiveness are from 24.1% to 51.3% at the density ratio of 1, while the improvements are from 1.3% to 36.8% at the density ratio of 1.5. The reason is that the swirling in the coolant breaks the symmetricity of counter-rotating vortex pairs, leading to a deviation of streaks of film coverage and better attachment under high blowing ratios. However, due to the swirl, film cooling effectiveness for two rows of staggered holes is decreased, because the swirl turns the coolant flow direction and creates poor coolant coverage areas between adjacent holes, and weakens the coolant accumulation and re-attachment at further downstream area