Transonic flow in a rotating turbine cascade of large pitch to chord ratio.

Abstract

A rotating turbine cascade was designed to simulate the nearly two dimensional flow past a flat plate turbine cascade of large pitch to chord ratio. The turbine was tested in the transonic flow range for flow incidence angles varying from 0 to egrees relative to the rotor and relative exit Mach numbers varying from 0.75 to 1.25. The measurements were made with special reference to the quasi three dimensional effects in the cascade through detailed radial traverse downstream of the rotor. The measuring probes were calibrated in a specially built calibrating rig where the effects of wall proximity were simulated due to its importance in internal flow measurements. Large effects of wall proximity on the calibration constants were noticed. The final effect on the determination of local Mach number etc., was not great. However wall proximity effects greatly influenced the value of the loss coefficients which depend on measured differences in pressure. The data evaluation methods were extended to allow for non two dimensionality. These modifications gave good agreement with the actual local measurements of flow angle variation. The evaluation of loss coefficients was also improved but not with the same degree of agreement as with the flow angles. Unsteady wall pressure measurements with rapid response transducers were made to obtain the pressure field in tip region relative to the rotating blade. The tangential blade force estimated from these unsteady pressure measurements agree well with that obtained from the measured momentum changes at the tip. Computations have also been made of the transonic flow field and compared with the measurements. The measurements are discussed in detail and suggestions made for better agreement of rotating cascade tests with the corresponding two dimensional cascades.