On the prediction of unsteady forces on gas-turbine blades. Part 1: Typical results and potential-flow-interaction effects

Abstract

This paper is a contribution to the study of the generation of unsteady forces on turbine blades due to potential-flow interaction and viscous-wake interaction from upstream blade rows. A computer program is used to compute the unsteady forces on a rotor. The accuracy of the computer program is tested by comparing the results of a steady-flow calculation case and of an unsteady-flow calculation case with theory and experiment respectively. Results are shown for typical stator-to-rotor-pitch ratios and stator outlet-flow angles. These results show that the first spatial harmonic of the unsteady force may decrease for higher stator-to-rotor-pitch ratios. This trend is explained by considering the mechanisms by which the unsteady forces are generated. In this paper the mechanism by which the potentialflow interaction affects the flow field to generate these unsteady forces is shown to vary with the stator-to-rotor-pitch ratio and with the outlet flow angle of the stator.