A Review of the Performance of Exhaust Systems for Gas-Turbine Aero-Engines

Abstract

This paper summarizes published information concerning the aerodynamic performance of exhaust diffusers and propelling nozzles for turbine aero-engines, and extends and supplements this with additional data obtained from tests made at the National Gas Turbine Establishment (N.G.T.E.). The factors influencing the exhaust system design are reviewed and the effects of the type of engine installation and the use of reheat are discussed. The influence of ducting losses on the thrust are then considered in terms of their effect on the performance of a typical turbo-jet engine. The paper continues with a review of some previous work on turbine exhaust diffusers, which was concerned with the effects of the diffuser area ratio and wall shape and with the effect of inlet swirl. This has since been extended by experimental examination of the influence of the bullet support struts on the performance of an engine, and the results of these tests are given. Little published information is available concerning the performance of propelling nozzles over the range of pressure ratio relevant to the turbo-jet engine. The results of tests up to a pressure ratio of 9 on a series of convergent-divergent nozzles are given and the effects of design pressure ratio and divergence angle are illustrated. A one-dimensional theoretical treatment is used to show the relationship between the non-dimensional and specific thrusts and the applied pressure ratio. The test results are then analysed in terms of these thrust parameters and their related coefficients. The paper concludes with reference, in general terms, to some of the more important mechanical engineering considerations which arise in the design of exhaust-duct installations in jet-propelled aircraft.