VELOCITY AND REYNOLDS STRESSES IN A PRECESSING JET FLOW

A novel fluid mixing device, described elsewhere, has been shown to ha ve 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 degrees and 60 degrees from the nozzle axis and its precession about that axis. Many of the factors governing the nozzle instabilities whic h drive the mixing in the external field are imprecisely defined. It i s the aim of the present paper to examine, in isolation from the nozzl e 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 pre sent investigation replaced by a mechanical rotation of a nozzle from which is emerging a jet which is orientated at an angle from the nozzl e axis. By this means the effect of precession on the deflected jet ca n be investigated independently of the phenomena which cause the prece ssion. The experimental data reported here has been obtained from meas urements made using a miniature, rapid response four-hole ''Cobra'' pi tot probe in the field of the precessing jet. Phase-averaged three dim ensional velocity components identify the large scale motions and over all flow patterns. The measured Reynolds stresses complement the veloc ity data and are found to be compatible with the higher entrainment ra tes of the jet found in earlier investigations.