Some aspects of the noise generated internally by a turbojetengine are considered analytically and experimentally. The emphasisis placed on the interaction of pressure fluctuations and entropy fluctuations,produced by the combustion process in the engine, withgradients in the mean flow through the turbine blades or the exhaustnozzle.
The one-dimensional interaction of pressure fluctuations andentropy fluctuations with a subsonic nozzle is solved analytically. Theacoustic waves produced by each of three independent disturbancesare investigated. It is seen that results for a large number of physicallyinteresting nozzles may be presented in a concise manner.
Some of the second-order effects which result from the areavariations in a nozzle are investigated analytically. The interactionof an entropy wave with a small area variation is investigated and thetwo-dimensional duct modes, which propagate away from the nozzle,are calculated.
An experiment is described in which one-dimensional acousticwaves and entropy waves are made to interact with a subsonic nozzle.The response of the nozzle to these disturbances is measured andcompared with the response as calculated by the analytical model.
The interaction of two-dimensional entropy waves with a subsonicnozzle and with a supersonic nozzle is investigated experimentally.The results are explained in terms of an analysis of the acousticwaves and entropy waves produced by a region of arbitrary heataddition in a duct with flow.
