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. 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

Mixing Analysis of Like Doublet Injectors in High Pressure Environments for Gelled Propellant Simulants

“…Data on dissimilar orifice diameter impingement case will follow. The continual increase of mixing extent at the lowest jet velocity can be attributed to a decreasing break-up length [34] and longest contact time. Decreasing break-up length means increased turbulent dispersion which contributes to better mixing.…”

“…[4] The contact time dictates the duration at which droplets can mix microscopically. Mixing efficiency does not change as the ambient pressure changes at higher jet velocities because break-up length does not decrease as much as lower jet velocities [27,34], meaning the pre-atomization and post-atomization break-up regimes are roughly the same and contact time is fixed for a set velocity. For a given equal jet velocity, the non-gelled fluid has greater momentum due to its higher density and generally more jet turbulence than that of the gelled mixture.…”

“…Other authors [32,33] have noted similar trends but have used different non-Newtonian fluids to create regime diagrams and to characterize atomization in atmospheric ambient conditions. The work of Ramasubramanian et al [34] covers both of these topics but adds elevated ambient pressure effects to their analysis.…”

Hydrous Ethanol Atomization by Impinging Jets

“…Impinging jets have been extensively studied until nowadays (Deng et al, 2018) (Negri and Ciezki, 2016) (Ramasubramanian et al, 2015) (Connell et al, 2018) (Chen and Yang, 2019). Impinging jets are used by their easy of manufacture and simultaneous good atomization and mixing to achieve an efficient mixing and burning of propellants.…”

Experimental Study of Atomization by Impinging Jets of Liquid and Gelled Green Propellants

“…Impinging jets have been extensively studied since last century until nowadays (Deng et al (2018), Negri and Ciezki (2016), Ramasubramanian et al (2015), Connell et al (2017), Yang et al (2019)). Impinging jets are used by their easy of manufacture and simultaneous good atomization and mixing to achieve an efficient mixing and burning of propellants.…”