Developments in Methods of Measuring Stresses in Compressor and Turbine Blades on Test Bed and in Flight

Abstract

An organization is described that has been operating for some years in connection with investigating vibratory and transient stresses in aero-engines. A large proportion of the work is being done on compressors and turbines and information is given upon some of the factors controlling the life of high-temperature gauges on them both. Some techniques are described that are being currently used for a very big volume of testing at the Rolls-Royce works in Derby and are generally those which have been developed since the author's paper on turbine measurements read in America in 1951 (Drew 1952)†. The system used at Rolls-Royce for a large proportion of tests of vibratory stresses is viewed by having one, and more recently two, recording rooms connected to all experimental test beds and a number of rigs by permanently installed cables. Particular reference is made to the various forms of slip-rings in general use. The relative advantages of telemetering signals from aircraft to the ground and of obtaining flight measurements with an airborne multi-channel recorder are discussed. Reproductions of records of rotating stall bands with their associated bands of high stress in the compressor are given, together with a brief description of the nature of rotating stall and the methods available for reducing troubles caused by it. A small change in the running conditions to move the working point of the compressor has a very marked effect upon compressor blade stresses and in studying this either on the test bed or in flight it is vital to have a very precise knowledge indeed of the instantaneous fuel flow, rev/min and blower pressure at the instant of high compressor blade stress during a rapid acceleration. A brief note on the results of the numerous tests which are being made is given, with a reference to a much fuller paper (Pearson 1953).