Comparison of Experimental and Theoretical Results for Unsteady Transonic Cascade Flow at Design and Off-Design Conditions.

Abstract

This paper presents experimental and theoretical results for turbine cascades performing harmonic oscillations in transonic flow at design and off-design conditions. The experimental investigations were performed in an annular test facility where unsteady blade pressures were measured in two different test cascades, one operating at the nominal inlet flow angle, the other at an incidence angle exceeding the normal value by more than 20 degrees. The corresponding theoretical results were computed with a 2D Euler code which makes use of flux vector splitting in combination with a time-dependent grid generation. The present data were all obtained for tuned bending modes where the blades performed heaving oscillations with the same frequency and amplitude, but with a constant interblade phase angle. For the cascade operating at design conditions, the steady flow was purely subsonic. The other test cascade was run in transonic flow, and a normal shock appeared on the rear part of the blade's suction surface. It was found that measured unsteady pressure and damping coefficients are well reproduced by the computedresults for the first test cascade. In the case of steady off-design flow (the second test cascade), significant differences between experimental and theoretical results are observed.