Experimental investigation on the effects of hole pitch and blowing ratio on the leading edge region film cooling of a rotating twist turbine blade

Abstract

An experimental investigation has been performed to study the effects of the hole pitch and the blowing ratio on the leading edge region film cooling performance of a twist turbine blade with three rows of film holes under rotating conditions. The experiments were accomplished in a test facility with one-stage turbine using the thermochromic liquid crystal (TLC) technique. All tests were made at a rotating speed of 574 r/min with the average blowing ratio ranging from 0.5 to 2.0. The Reynolds number based on the mainstream velocity of the turbine outlet and the rotor blade chord length was fixed at 6.4 × 104.CO2 was used to obtain the coolant-to-mainstream density ratio of 1.56. The hole pitches tested were p=2.5d,p=3.75d and p=5d, respectively. The results show that both the hole pitch and the blowing ratio play an integral role in determining the film cooling effectiveness distributions on the leading edge. Regardless of the hole pitch, the spanwise average film cooling effectiveness increases monotonously with the increase of blowing ratio on the leading edge region. For all blowing ratio cases, the spanwise average effectiveness has a decreasing trend as the hole pitch increases. When the bowing ratio is constant, the difference between the spanwise average film cooling effectiveness value obtained in the region of −4.3<x/d<0 and the region of 0 < x/d < 3.75 has a decreasing trend as the hole pitch increases. For all hole pitch cases, the area average film cooling effectiveness increases monotonously as the blowing ratio increases. For all blowing ratio cases, the area average film cooling effectiveness decreases monotonously as the hole pitch increases. However, the reduction is not always linear to the hole pitch change. When the coolant jet mass flow rate is constant, the p=2.5d case provides a higher level of the area average film cooling effectiveness than the p=3.75d and 5d cases.