Combustor and Single-Stream Jet Noise Prediction for a Newly Designed Turbojet Engine by Using Semi-Empirical Methods

Abstract

Research is being carried out at the Technological Institute of Aeronautics to provide the support for the design of high performance gas turbines, including noise prediction by means of theoretical and empirical methods. Emphasis is given to new engines noise prediction, to anticipate problems at very early design stage and to take the necessary actions to guarantee that the engine noise is below the imposed limits. Noise prediction is part of the high fidelity engine performance prediction computer program, which provides the designer, at any time during the design phases, with information on the noise levels generated by each component and by the engine. Research indicates that the combustor and the propelling nozzle are major noise sources, so that these two components of a turbojet engine were dealt with in this work. The far-field one-third octave band sound pressure levels, (SPL), and overall sound pressure level (OASPL) are calculated, for several observer positions and engine rotational speeds. A 5 kN turbojet engine under development serves as the basis for the noise prediction. The influence of the observer position on SPL and OASPL for steady engine operation, as well as the effect of the engine rotational speeds on the engine noise generated by the combustor and the propelling nozzle are presented, which are in agreement with the noise of similar engines. Ground reflection and atmospheric attenuation were not considered. A high fidelity engine performance prediction computer code incorporates the noise prediction methodology whose results are reported in this paper.