Computation of the Unsteady Transonic 2D Cascade Flow by an Euler Algorithm with Interactive Grid Generation.

Abstract

This paper presents the numerical results of a code for computing the unsteady transonic flow in a 2D cascade of harmonically oscillating blades. The calculation of the flow field is based on an Euler code using flux vector splitting. After a description of the basic equations and the special numerical techniques applied in the code, results are presented for the first harmonics of pressure, lift and moment coefficients. For the present investigations, two basic oscillation modes were chosen: tuned modes where all blades perform oscillations with the same frequency, same amplitude and a constant interblade phase angle, and mistuned modes, where all blades are oscillating with the same amplitude, but with varying frequency from one blade to another. The computed results refer to two standard configurations given by the IUTAM "Workshop on Aeroelasticity in Turbomachine Cascades", one of which is a subsonic-transonic turbine cascade, and the other is a subsonic-transonic compressor cascade. In the case of tuned bending modes, the theoretical results are compared with the experimental data from the turbine standard configuration. Special attention is directed to the occurrence of aerodynamic instability in the oscillating cascade. It can be shown that the interblade phase angles, at which the above-mentioned experimental test case shows unstable behavior, are generally well-reproduced by the computational results.