Effect of Unsteady Wake With Trailing Edge Coolant Ejection on Detailed Heat Transfer Coefficient Distributions for a Gas Turbine Blade

Abstract

Detailed heat transfer coefficient distributions on a turbine blade under 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 axial chord is varied from 5.3 × 105 to 7.6 × 105 for a five blade linear cascade in a low speed wind tunnel. Unsteady wakes are produced using 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 ratio of the jets to free-stream is varied from 0.0 to 1.0. Results show that the surface heat transfer coefficient increases with an increase in Reynolds number and also increases with the addition of unsteady wakes. Adding grid generated turbulence to the unsteady wake further enhances the blade surface heat transfer coefficients. The trailing edge jets compensate the defect in the velocity profile caused by the unsteady passing wakes and give an increase in free-stream velocity and produce a more uniformly disturbed turbulence intensity profile. The net effect is to increase both the front parts of blade suction and pressure surface heat transfer. However, the jet effect diminishes in and after the transition regions on suction surface, or far away from the leading edge on pressure surface.