Analytical investigation of the effects of water ingestion on the performance of an axial-flow compressor

This investigation attempts to determine the effects of water ingestion on the performance of an axial-flow compressor, by developing an analytical model to simulate the steady-state aerothermodynamics of a compressor. The effects of water ingestion on compressor performance are determined by comparing the gas phase static and total properties, axial velocity, stage power input, and blade row diffusion factor for a test case, to a dry air reference case. The simulated compressor represents a compressor that is mounted on a constant-speed compressor test rig in an aeropropulsion test facility. The compressor is fitted with a bell-mouth inlet and a variable-area throttle valve, that is held constant, at the compressor design choking area, for all tests. The compressor is assumed to ingest saturated air, and 2, 4, 6, 8, or 10 percent liquid water, by mass. The FAA engine acceptance test requires engine operation with 4 percent liquid water ingestion by mass, however, a severe rain storm may contain up to 15 percent liquid water by mass [1-12]. The analytical model of the compressor flow is a two-phase, one-dimensional model in which the compressor is assumed to be isentropic. The compressor is assumed to be isentropic to make the simulation tractable, and to prevent losses from obscuring the water ingestion effects. Although, water ingestion effects are accompanied by losses, this approach illuminates the fundamental effects of water ingestion on compressor performance. Some of the main conclusions drawn from the analytical model are:

1) The compressor total pressure ratio, and the compressor total temperature ratio decreased with the ingestion of liquid water.

2) The compressor power input decreased with the ingestion of small amounts of liquid water, but increased with the ingestion of larger amounts of liquid water.

3) The axial velocity increased rapidly, and the blade row diffusion decreased rapidly, in the later stages of the compressor, when liquid water was ingested. This may lead to blade row stall in the later stages of the compressor.