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. Nomenclature= breakup length, mm n = power law index P = pressure, MPa Q = flow rate, cm 3 ∕ min Re g = Reynolds number of the jet weighted for density ratio; ρ g U j D o ∕μ Re j = Reynolds number of the jet; ρ j U j D o ∕μ U = velocity, m∕s We g = Weber number of the jet weighted for gas density; ρ g U 2 j D o ∕σ We j = Weber number of the jet; ρ j U 2 j D o ∕σ γ = shear rate, s −1 η = non-Newtonian viscosity η ∞ = non-Newtonian viscosity at infinite shear rate Θ = half-impingement angle of liquid jets, deg λ = wavelength, mm μ = Newtonian viscosity, Pa · s ρ = density, kg∕m 3 σ = surface tension, N · m −1 τ o = yield stress, Pa Subscripts c = critical g = gas gen = generalized GHP = gelled hypergolic propellant HBE = extended Herschel-Bulkley j = jet

No abstract

Impinging doublet injectors offer rocket designers an effective way to atomize and mix opposing jets of fuel and oxidizer. The adaptability of the injector designs and ease of manufacturing make them attractive choices for designers. The adaptability of injector designs introduces many variables to the system like orifice diameter, nozzle orifice pairings, and working fluid to name a few. This expanse of variables requires This work would not have been possible without the support from United States Army Research Office under the Multi-University Research Initiative. I would like to thank Dr. Jong Guen Lee for allowing me this graduate opportunity and for his academic support through my undergraduate studies and my graduate research. I would also like to thank my committee members of Dr. San-Mou Jeng and Dr. Milind Jog. I appreciate them taking time and effort to apply their expertise to critiquing my work. There are a few students and a staff member I would like to thank for their help with experimentation. The student members are Chandra Ramasubramanian, Charlie Hinton, Jake Keller, Vaughn Bostwick, Andrew Stubblebine, Wessam Estefanos and Jun Hee Han. They were invaluable help during setup and testing. The staff member is Curt Fox who without his help, I would have been able to work as efficiently and as safely. Lastly, I want to thank my friends and family for their support throughout my academic journey.