Aerodynamic loss characteristics of a turbine blade with trailing edge coolant ejection: Part 1- Effect of cut-back length, spanwise rib spacing, free-stream Reynolds number, and chordwise rib length on discharge coefficients

The internal fluid mechanics losses generated between the blade plenum chamber and a reference point located just downstream of the trailing edge are investigated for a turbine blade trailing edge cooling system. The discharge coefficient C_d is presented as a function of the free-stream Reynolds number, cut-back length, spanwise rib spacing, and chordwise rib length. The results are presented in a wide range of coolant to free-stream mass flow rate ratios. The losses from the cooling system show strong free-stream Reynolds number dependency, especially at low ejection rates, when they are correlated against the coolant to free-stream pressure ratio. However, when C_d is correlated against a coolant to free-stream mass flow rate ratio, the Reynolds number dependency is eliminated. The current data clearly show that internal viscous losses due to varying rib lengths do not differ significantly. The interaction of the external wall jet in the cutback region with the free-stream fluid is also a strong contributor to the losses. Since the discharge coefficients do not have Reynolds number dependency at high ejection rates, C_d experiments can be performed at a low free-stream Reynolds number. Running a discharge coefficient experiment at low Reynolds number (or even in still air) will sufficiently define the high blowing rate portion of the curve. This approach is extremely time efficient and economical in finding the worst possible C_d value for a given trailing edge coolant system.