Experimental investigations of the effects of the injection angle and blowing ratio on the leading-edge film cooling of a rotating twisted turbine blade

Experimental investigations were performed to study the effects of the injection angle of cylindrical holes and the blowing ratio on the leading-edge-region film cooling of a twisted turbine blade under rotating conditions. The experiments were carried out at a test facility with a 1-stage turbine using the thermochromic liquid crystal (TLC) technique. All experiments were performed at a rotating speed of 574 rpm with an average blowing ratio ranging from 0.5 to 2.0. The Reynolds number was fixed at 6.3378 × 10⁴ based on the mainstream velocity of the turbine outlet and the rotor blade chord length. CO₂ was used as the coolant to achieve a coolant-to-mainstream density ratio of 1.56. The film-hole injection angles tested were 30° 45° and 60°. The results show that both the injection angle and the blowing ratio have significant impacts on film cooling effectiveness. For α = 30° and α = 45° the radial average film cooling effectiveness increases as the blowing ratio increases in all regions. For α = 60° this effectiveness first increases and then decreases as the blowing ratio increases, with the case of M = 1.5 yielding the best average cooling performance. At each blowing ratio, the α = 30° case always yields the highest streamwise average film cooling effectiveness in the region of −4.3 < X/D < 2. For 2.75 < X/D < 3.75, the effectiveness first increases and then decreases as the injection angle increases. For α = 30° and α = 45° the area average film cooling effectiveness monotonously increases as the blowing ratio increases. For α = 60° this effectiveness first increases and then decreases as the blowing ratio increases from 0.5 to 2.0, with the best blowing ratio M = 1.5. Under the same blowing ratio, the α = 30° case always yields the highest area average film cooling effectiveness in the leading edge region.