Effect of unsteady wake with trailing edge coolant ejection on detailed heat transfer coefficient distributions for a gas turbine blade
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Detailed heat transfer coefficient distributions under the combined effects of trailing edge jets and unsteady wakes on turbine blade heat transfer under various free-stream conditions are presented using a transient liquid crystal image method. The exit Reynolds number based on the blade chord is varied from 7.1 105 to 1.02 106 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 ejection holes located in the hollow spokes of the wake generator. The mass flux ratio of the jets to the 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. The passing of an unsteady wake on the blade promotes earlier and broader transition on the suction side of the blade. Results also show that an increase in the unsteady wake Strouhal number reduces local spanwise variation of heat transfer coefficients over the blade surface. 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 cause an increase in mainstream velocity and produce a more uniform turbulence intensity profile. The net effect is to increase both the pressure side and suction side heat transfer. However, the jet effect diminishes in the transition and fully turbulent regions.
