Characterization of Near-Field Spray of Nongelled- and Gelled-Impinging Doublets at High Pressure

Abstract

Atomization mechanism of gelled propellants in an impinging jet flowfield is significantly different from that of nongelled liquid propellants and is not clearly understood. This study explores the effect of liquid fluid properties such as viscosity and surface tension on the liquid sheet breakup with a special emphasis on the effect of ambient pressure. A rheologically matched non-Newtonian fluid that is nonreactive and nontoxic is used as a simulant for the gelled hypergolic propellants. Near-field spray characteristics such as the sheet formation and breakup length of the liquid sheet are experimentally determined using shadowgraph. Various sheet breakup regimes have been identified for both nongelled and gelled simulants over a range of flow conditions. For all fluids, the breakup length is found to decrease as the ambient pressure increases. Near-field imaging and its analysis show that the ambient pressure affects jet surface dynamics before impingement by increasing the jet surface disturbance length scale and sheet dynamics after impingement by shortening the surface wavelength, resulting in shorter breakup length with the increase of ambient pressure.