EFFECT OF UNSTEADY WAKE WITH TRAILING-EDGE COOLANT EJECTION ON DETAILED HEAT-TRANSFER COEFFICIENT DISTRIBUTIONS FOR A GAS-TURBINE BLADE

Detailed heat transfer coefficient diistributions on a turbine blade u nder the combined effects of trailing edge jets and unsteady wakes at various free-stream conditions are presented using a transient liquid crystal image method. The exit Reynolds number based on the blade axia l chord is varied from 5.3 x 10(5) to 7.6 x 10(5) for a five blade lin ear cascade in a low speed wind tnnnel. Unsteady wakes are produced us ing a spoked wheel-type wake generator upstream of the linear cascade. Upstream trailing edge jets are simulated by air ejection from holes located on the hollow spokes of the wake generator. The mass flux rati o of the jets to free-stream is varied from 0.0 to 1.0. Results show t hat the surface heat transfer coefficient increases with an increase i n Reynolds number and also increases with the addition of unsteady wak es. Adding grid generated turbulence to the unsteady wake further enha nces the blade surface heat transfer coefficients. The trailing edge j ets compensate the defect in the velocity profile caused by the unstea dy passing wakes and give an increase in free-stream velocity and prod uce a more uniformly disturbed turbulence intensity profile. The net e ffect is to increase both the front parts of blade suction and pressur e surface heat transfer. However, the jet effect diminishes in and aft er the transition regions on suction surface, or far away from the lea ding edge on pressure surface.