The operating range of compressors is normally curtailed by the occurrence of stall. Stall can sometimes be delayed, and the operating range increased, by the use of treatment on the casing over the rotor tips. It has been widely accepted in the past that the improvement in stall margin caused by the treatment was approximately linearly proportional to the loss in efficiency it produced. An experimental and numerical investigation has been carried out on the type of treatment which has been found to be the most promising, namely axial skewed slots. The increase in range and loss has been predicted by the Dawes un_NEWT code

Recent work has shown that designs of treatment are possible for which there is little or no loss in efficiency, and has established more clearly how the treatment delays stall and how loss is created. Current work will look at the behaviour in the presence of inlet and outlet flow distortion.

The work is supported by Rolls Royce and the Department of Trade and Industry.

Nick Cumpsty, Tom Hynes

The intake of a modern high bypass ratio turbofan is usually asymmetric and drooped relative to the centreline of the engine. The asymmetry that this imposes on the flow at entry to the fan is a major item of interest to manufacturers. It has a potentially serious impact on performance, on vibration and on noise. This project is aimed at developing ways of modelling a fan performing in such an asymmetric flow, using three-dimensional calculations of the flow in the intake together with various fan models. These fan models range from developments of actuator disks to coarse three-dimensional calculations of the flow within blade-rows. Results show, in general, excellent agreement with engine test data. Other sources of asymmetric engine flow, such as pylons, support struts and asymmetric stators are also accommodated within this framework. Current work is aimed at using the results from this type of calculation to assess the effect of asymmetry on flow stability.

Tom Hynes

Future ASTOVL aircraft may well incorporate some sort of lift fan mounted in the aircraft body or wing. This project has essentially two aims. The first is to develop calculation methods to predict the effect of the presence of the fan on the aerodynamics of the aircraft. The second is to investigate ways of assessing the effect of the presence of a necessarily highly non-ideal inlet on the lift engine performance. The techniques under development are suitable for a wide variety of turbomachinery applications involving rotating machinery and complicated inlet and exhaust geometry.

Tom Hynes (Jonathan Taylor)