Prediction of Acoustic, Vorticity and Entropy Waves Generated by Short-Duration Acoustic Pulses Incident on a Blade Row

Abstract

Some long-standing questions concerning the dynamic behavior of coupled inlet/compressor systems have been answered by analyzing data from recent experiments in which the reflections of intense, short-duration acoustic pulses from an operating compressor were documented. The present paper offers a simple, one-dimensional integral theory as a background for these experiments. The arrival of an acoustic pulse (or an acoustic step change) to a single row of stationary blades gives rise to two acoustic waves (one upstream and one downstream), one vorticity wave, and possibly also an entropy wave. Pulses are characterized by integrals of spatial distributions of pressure, temperature or tangential velocity, while steps are defined by the jump of these flow properties at the wave. Simple expressions are given for the strength of each wave type, in terms of the blade stagger angle and the axial Mach number. The results help in interpreting, scaling and extrapolating experimental data. The work is a step towards an ability to specify realistic outflow boundary conditions in unsteady inlet flow computations, as appropriate for the compressor geometry and the operating conditions.