Effect of unsteady wake with trailing edge coolant ejection on film cooling performance for a gas turbine blade

The effect of unsteady wakes with trailing edge coolant ejection on surface heat transfer coefficients and film cooling effectiveness is presented for a downstream film-cooled turbine blade. The detailed heat transfer coeffic ient and film effectiveness distributions on the blade surface are obtained using a transient liquid crystal technique. Unsteady wakes are produced by a spoked wheel-type wake generator upstream of the five-blade linear casca de. The coolant jet ejection is simulated by ejecting coolant through hobs on the hollow spokes of the wake generator. For a blade without film holes unsteady wake increases both pressure side and suction side heat transfer l evels due to early boundary layer transition. Adding trailing edge ejection to the unsteady wake further enhances the blade surface heat transfer coef ficients particularly near the lending edge region. For a film-cooled blade , unsteady wake effects slightly enhance surface heat transfer coefficients but significantly reduces film effectiveness. Addition of trailing edge ej ection to the unsteady wake has a small effect on surface heat transfer coe fficients compared to other significant parameters such as film injection, unsteady wakes, and grid generated turbulence, in that order. Trailing edge ejection effect on film effectiveness distribution is stronger than on the heat transfer coefficients.