A research program is in progress to extend the compressor stall inception model recently published by Camp and Day. The model draws a clear line between the two much debated stall inception patterns and sets out the conditions under which each of the patterns will occur. This work has highlighted the role of radial flow distribution in determining the type of stall inception pattern. A series of tests are currently being done to investigate the influence of high tip loading as opposed to high hub loading. The nature and magnitude of losses generated at the tip and hub sections of the blading is also being studied with a view to understanding their influence on the shape of the overall characteristic - and hence on the stability of the compressor. The ultimate aim is to identify those flow conditions which are most likely to cause premature stalling.

This project is sponsored by Rolls-Royce.

Ivor Day

Hub cavity slots exist in most aero-engine compressors to allow for the relative motion between the rotor disc and the stator shroud ring. In some cases the slots are relatively large to allow for differential expansion between the compressor shaft and the casing. The pressure field associated with each blade in a stator row, for instance, drives flow into and out of the adjacent slot cavity. In most cases the flow leaving the slot will have a detrimental effect on the secondary flow in the stator hub corner. These effects are being studied experimentally in a linear cascade and in a working compressor.

This work is sponsored by Rolls-Royce

Ivor Day (Albert Demargne)

All aero-engines encounter heavy rain and hail from time to time and are expected to continue operating safely under these conditions. In general, the time during a flight cycle when the engine is most susceptible to the effects of water ingestion is during low power descent from 6000m to 1500m where atmospheric water and hail are at their greatest concentration. Work is in progress to investigate the effects of water ingestion on engine performance - particularly at low power settings. Experiments are planned to look at the mechanical interaction of water droplets with the moving and stationary blade rows in the compressor and to assess the effects of surface films on the aerodynamic performance of the aerofoils. These details will be combined with thermodynamic calculations for two-phase flows to produce a realistic computer model of compressor performance under wet conditions.

This work is sponsored by Rolls-Royce

Ivor Day and John Young