Effect of nozzle geometry on the atomization and spray characteristics of gelled-propellant simulants formed by two impinging jets

Near- and far-field atomization processes of impinging doublets are experimentally characterized using nongelled and gelled water as working fluids. The main emphasis of the study is on the effect of nozzle geometry, such as orifice inlet shape and aspect ratio, on jet stream surface dynamics and break-up processes before and after jet impingement, respectively. Gelled water jets (non-Newtonian), due to increased viscosity, display fewer surface disturbances than nongelled water jets (Newtonian). As a result, for a given flow rate the sheet formed by impinging jets is much more stable, and the corresponding break-up length is much greater for gelled water than for nongelled water jets. The nozzle aspect ratio has a more significant effect on the near-field jet stream characteristics for both fluids than the orifice inlet shape. Longer nozzles (l/d = 20) form more stable jet streams and delay the breakup of sheets, leading to greater breakup length than that attained with shorter nozzles (l/d = 5). For similar Reynolds numbers and hence, much higher respective flow rates, the droplet size for gelled water is much smaller than that for nongelled water. Also, impinging jets employing gelled water produce sprays with greater spatial distributions and wider ranges of droplet size than jets with nongelled water.