ROLES OF INITIAL CONDITION AND VORTEX PAIRING IN JET NOISE

This is a study of the effect of initial condition on sound generated by vortex pairing in a low Mach number, cold air jet (0. 15 less than equivalent to M less than equivalent to 0. 35). Data has been taken, for both flow velocity fields and sound pressure far fields, in a quality anechoic facility, with careful documentation of the effect of initial condition on the sound field of jets of two different geometries (i. e. , circular and elliptic). Explanations are presented for most of the observed effects by applying Moehring's theory of vortex sound to vortex filament models of coherent structures in the jets. The primary contribution of this paper is to examine quantitatively the role of vortex pairing in the production of jet noise; the results are used to reemphasize that 'pairing noise' cannot be dominant in most practical jet sound fields, contrary to claims by other researchers.