On source coherence affecting jet noise

The effect of source coherence on jet noise has been investigated theoretically by means of the Lighthill approach and using suitable cross-correlation functions for the source quantity. It is found that for increasing source coherence the noise radiation at radiation angles near to the jet axis is augmented, but is reduced normal to the jet axis. For subsonic convection of turbulence, the radiated sound power is increased for small Strouhal numbers, but strongly reduced for higher. For convection Mach numbers about unity, however, the power is always augmented by increasing source coherence.

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