A Study of Unsteady Pressures Near the Tip of a Transonic Fan in Unstalled Supersonic Flutter

Abstract

A comparison of experimental and theoretical results is presented for a modern transonic research fan, vibrating in a coupled flutter mode. The measurement of steady and unsteady pressures on the aerofoil surface is described, as also is the derivation of the accompanying blade motion using casing-mounted frequency modulated grids. This complex motion is made use of to calculate unsteady pressures from various unsteady aerodynamic theories. These theoretical models are reviewed in turn and compared against the experimental data at a reference blade section. Considering the complexity of the flow and the inherent simplifying assumptions, the comparisons on both amplitude and phase are generally favorable. The position of the shock in the blade passage is shown to be important. The comparison is extended to unsteady work and again the results are favorable if allowance is made for the differences in blade pressure ratio between the various theories and the experiment.