A Comparison of Three Low Pressure Turbine Designs

Abstract

As part of the current research, three low pressure turbine (LPT) geometries—which were designed with a common pitch, axial chord, inlet angle, and exit Mach number and to create the same nominal level of turning—are compared. Each of the LPT cascades was investigated under a range of Reynolds numbers, exit Mach numbers, and under the influence of a moving bar wake generator. Profile static pressure distributions, wake traverses at 5% and 40% axial chord downstream of the trailing edge, and suction side boundary layer traverses were used to compare the performance of the three designs. The total pressure losses are strongly dependent on both the maximum velocity location as well as the diffusion on the suction surface. The importance of the behavior of the pressure surface boundary layer turned out to be negligible in comparison. Cases with equivalent operating Reynolds number and suction side diffusion level are compared in terms of the total pressure losses that are generated. It is shown that a relationship between loss and suction side maximum velocity location exists. An optimum suction side maximum velocity location depends on the Reynolds number, diffusion factor, and wake passing frequency.