Shock Induced Flutter of Turbomachinery Blade Row

Abstract

This paper describes the influence and effect of a normal shock wave on the flutter characteristics of a turbomachine blade row. High fidelity numerical analysis is used to calculate the energy exchange for a vibrating blade row in the presence of an oscillating normal shock wave. The 3-D Tenth Standard Cascade is used in the present study to calculate the influence of a shock on the energy exchange of blades undergoing a torsional vibration and to correlate the observations with an algebraic model. Effect of three parameters-distance of shock from elastic axis, inter-blade phase angle and vibration frequency are investigated. The results indicate that the three parameters strongly influence the flutter characteristics. The distance between shock location and elastic axis was found to have a linear effect on stability. Moving the elastic axis from downstream of the shock to upstream changes the sign of the stability characteristics as well. It was found that the shock induced energy exchange varied harmonically with inter-blade phase angle indicating the phase between shock motion and blade motion to be independent of inter-blade phase angle. The influence of vibration frequency on work done by the shock was found to be harmonic for reduced frequencies up to 2. The results also showed that either a positive or negative energy exchange could be induced by a shock depending upon the frequency of vibration. The influence of the shock wave on the unsteady flowfield was found to be linear for small amplitude blade oscillation. It was also found that the region of influence of the shock on the work could be divided into primary and secondary regions with work in the primary region being influenced directly by the shock motion. The work in the secondary region was found to be influenced by flow variations induced by shock motion downstream of the shock.