Film cooling effectiveness of a leading-edge cooling array of a rotating turbine blade with twist

Experimental investigations have been carried out to study the effects of the film hole pitch-to-diameter ratio (P/ D), blowing ratio (M) and rotation on the leading edge (LE) region film cooling performance of a twist turbine blade under rotating conditions. The thermochromic liquid crystal (TLC) technology was applied to measure the LE surface temperature. All experiments were performed at the rotating speed of 574 r/min with the average M varying from 0.5 to 1.25. The Reynolds number (Re) based on the mainstream velocity of the turbine outlet and the test blade chord length was maintained at 6.4 x 104. The coolant-to-mainstream density ratio (DR) was 1.04 with N2 as the coolant. The hole pitch-to-diameter ratios tested were P/D = 2.5, P/D = 3.75 and P/D = 5.0, respectively. The experimental results indicate that both the P/D and the M play an indispensable role in influencing the film cooling performance on the LE under rotating conditions. Regardless of the value of film hole P/D, the spanwise average film cooling effectiveness (eta) increases gradually with increasing the M on the LE region under rotating conditions. For all hole P/D cases, the experimental results indicate that the level of spanwise average eta provided by the PS region (-4.3 < X/D < 0) is higher than that provided by the SS region (0 < X/D < 3.75) in the LE region when the M was unchanged under rotating conditions. For all M cases, the spanwise average eta indicates the decreasing trend with increasing the hole P/D. For all hole P/D cases, the area average eta increases gradually with increasing the M. For all M cases, the area average eta decreases gradually with increasing the hole P/D. And the reduction is sometimes non-linear to the P/D change. Under the condition that the coolant jet mass flow rate (MFR) remains constant, the area average eta decreases gradually with increasing the hole P/D.