Investigation of transonic steam turbine tip sections with various suction side blade curvatures

Theoretical and experimental results from studies of three transonic steam turbine rotor tip sections are presented. The aim is to evaluate the effect of various suction side curvatures on the blade performance at both design and off-design conditions. The experiments were conducted in a high speed cascade tunnel in the outlet Mach number range 0.8 to 1.7 with air as the working medium. The experiments included flow visualization tests using Schlieran photographs, detailed blade pressure distribution measurements, and blade performance measurements. The experimental blade velocity distributions and the outlet flow angles are compared with theoretical predictions obtained with a time marching method. Results confirm the usefulness of this time dependent finite area method in predicting performance of transonic blades. It is shown that any improvement of the design point performance by careful shaping of the suction side results in considerable reduction of the operating range.