Prediction and Measurement of Direct Combustion Noise in Turbopropulsion Systems

Abstract

The development of an improved prediction system for direct combustion noise is discussed. Expressions for acoustic power level, peak frequency, and full-scale engine acoustic transmission loss due to combustor/duct coupling and turbine attenuation are derived in terms of readily available performance and geometry parameters from the burner and turbine. New parameters introduced by the prediction system include the effects of fuel nozzle number and burner length. Predictions are in good agreement with noise data obtained from component rig tests on several JT8D burner configurations, and full-scale turbofan engines. The applicability of the system to the prediction of combustion noise levels, spectra, and directivity from full-scale engines is demonstrated for four PW i.e., the JT8D-109, JT9D-7A, JT9D-70, and the prototype JT10D.