Velocity and Reynolds stresses in a precessing jet flow

Abstract

A novel fluid mixing device, described elsewhere, has been shown to have a dramatic effect on the combustion characteristics of a fuel jet. The main features of the flow are the deflection of the jet between 30° and 60° from the nozzle axis and its precession about that axis. Many of the factors governing the nozzle instabilities which drive the mixing in the external field are imprecisely defined. It is the aim of the present paper to examine, in isolation from the nozzle instabilities, the influence of precession on a deflected jet as it proceeds downstream from the nozzle exit. The fluid dynamically driven phenomena within the nozzle which cause the precession are in the present investigation replaced by a mechanical rotation of a nozzle from which is emerging a jet which is orientated at an angle from the nozzle axis. By this means the effect of precession on the deflected jet can be investigated independently of the phenomena which cause the precession. The experimental data reported here has been obtained from measurements made using a miniature, rapid response four-hole “Cobra” pitot probe in the field of the precessing jet. Phase-averaged three dimensional velocity components identify the large scale motions and overall flow patterns. The measured Reynolds stresses complement the velocity data and are found to be compatible with the higher entrainment rates of the jet found in earlier investigations.