Experimental Investigation of Unsteady Pressure Behaviours in a Linear Turbine Cascade

Abstract

Unsteady flow effects have been investigated for sub-, trans- and supersonic exit flow conditions in a turbine cascade. Specifically, experimental forced bending blade vibrations—with one oscillating blade—were performed in a linear cascade. The blade frequency was 160 Hz. The resulting unsteady pressures were measured with piezoelectric pressure transducers along blade surfaces at mid-span and on the facility sidewall. The cascade is composed of five blades. The aims were: 1) to achieve a better physical understanding of unsteady pressure propagations within cascades; 2) to achieve a better understanding of disturbing influences on measurements in linear cascades; 3) to evaluate possible influences of tip clearance on unsteady measurements at blade mid-span; 4) comparison with existing prediction models for design and analysis and creation of a database of experimental data. Systematic investigations have been conducted in a linear facility for sub-, trans- and supersonic exit flow conditions to achieve the aims above. It was found that side-wall unsteady pressure measurements can provide a good indication of the unsteady behaviour throughout the cascade. For transonic exit flow conditions a tailboard influence can occur in the outlet cascade region. Single blade vibrations in turbine cascades produce a different pressure propagation behaviour in each of the two blade passages around the oscillating blade. The local damping at mid-span is not significantly influenced by a change in tip clearance or a slightly non-periodic flow.