Print version

Development of the Larzac Engine Rig for Compressor Stall Testing.

• Download this publication

Abstract

The development and upgrade of test installations, instrumentation and the data acquisition system of an existing turbofan engine test rig are described for an experimental program which was planned and initiated to investigate the transient unsteady operation of gas turbine engines with an emphasis on compressor operation. The objective of the program was to examine aerodynamic instabilities such as stall and surge. Of particular interest were the pre-stall behaviour of the compressor and the generation and the detection of gas-path stall/surge precursors. Methods used to invoke compressor stall/surge and to detect stall/surge precursors are described and examples of results of the observed stall/surge phenomena and their precursors are included. However, the precursor pressure pulses are of small amplitude and occur only several milliseconds prior to the point of stall initiation. Additional work is required to incorporate these results in a practical stall warning device.

Executive Summary

Stall and surge of turbo-machinery compressors has been a major concern to aircraft operators since the first gas turbine engines were introduced into service. Stall, on its own, sometimes undetected and unsuspected, is always detrimental to engine efficiency and performance. Combined with surge it can be sudden in onset, giving no warning and very rapidly lead to flameout, thrust loss and catastrophic mechanical failure. This is likely to occur in the presence of air flow disturbance, whilst the aircraft is manoeuvring or the pilot is demanding rapid changes of thrust. High ambient temperature is also a potential contributing factor. Stall and surge is unacceptable to a civil operator of multi-engined aircraft; to a military operator such an occurrence, particularly at low altitude, can be fatal. Unfortunately the circumstances where stall and surge are most likely to occur are frequently unavoidable during military operations, where, in addition to naturally occurring atmospheric and manoeuvring effects, another possible source of intake disturbance is ingestion of hot gases from gun discharge or missile launch.; Decades of development have produced engines with reduced stall and surge susceptibility, but have not eliminated stall and surge as potential causes of aircraft loss. Studies of the phenomena make it clear that it is unlikely to ever achieve total elimination of the problem. However, it may be possible to detect pressure disturbances in the engine intake air flow which provide a warning that the engine is approaching stall. Detected early enough these precursor disturbances might be used to initiate avoidance action.; This report describes the further development of an existing engine performance test rig to provide the capability to investigate stall and surge occurrences and to identify stall precursors. The rig is one of a very small number of such rigs in the world and is currently unique in Australia. The report details the operation of the overall rig and of the test engine and its control system. It also details the procedures for successful experimental testing and presents a selection of results obtained. These results show evidence of stall precursors, however these are of small amplitude and occur only a few milliseconds prior to the point of stall initiation. The report includes recommendations for future studies of stall and surge onset detection.

Back to the top