Analysis of the Effect of Heated Jet Flow on the Far Field Radiation From a Noise Source

Abstract

One factor which influences the radiation of jet noise is the interaction with the heated moving flow of a parallel twin jet. Because of the temperature and flow discontinuity between the jet and the surrounding air, the parallel jet acts as a partial barrier between the noise source and the receiver. An analytical model of jet shielding has been developed consisting of the sound field emitted from a stationary, discrete frequency point source, which impinges on a cylinder of locally parallel flow. The model is analyzed to identify the zones in which the various shielding mechanisms dominate. The effects of such parameters as jet temperature and flow speed are investigated. The analytical model is compared to experimental results for the shielding of a point noise source adjacent to a subsonic, isothermal air jet. The model estimates the trends of sound amplification and reduction by the jet in downstream azimuthal planes, showing lobe formations similar to those found experimentally. The model underestimates the shielding in the shadow zone at far downstream locations where sound diffraction is the dominant mechanism. Resolution of this discrepancy by way of modification of the shielding jet model is discussed.