THE EFFECT OF WALL THICKNESS ON NOZZLE SUCTION SIDE FILM COOLING

摘要

The effect of nozzle airfoil wall thickness on nozzle suction side film cooling effectiveness was experimentally investigated. The engine operating conditions were simulated in a scaled warm cascade, which was built based on industrial gas turbine nozzle airfoils. Film effectiveness distribution on the suction surfaces was obtained using the pressure sensitive paint (PSP) technique. Nitrogen gas was used to simulate cooling flow as well as a tracer gas to indicate oxygen concentration such that film effectiveness by the mass transfer analogy could be obtained. Two nozzle test models were investigated, which had similar cooling supply plenums. One of them had a wall thickness of 0.47cm and the other 0.63 cm. The nozzle vanes had showhead and film cooling holes on two suction side locations. Six cooling mass flow ratios (MFR, blowing ratios) were studied for each of the nozzle test models and two-dimensional film effectiveness distributions were obtained. Then the effectiveness distributions were spanwise averaged for comparison. For both cases, the overall film effectiveness increased with the MFR or the blowing ratio. Comparing the two models, the thicker wall (or the larger L/D value) resulted in improved film effectiveness for the lower MFR's. For the higher MFR, the better-developed jets due to the thicker wall (or the larger L/D) would cause a jet lift-off; therefore reduce the overall film effectiveness. The spanwise shifting pattern was also depended on the wall thickness.