No 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

Experimental results on the response of spray formed by the liquid (Jet-A) jet injection into a crossflow (Air) is presented with a special emphasis on its response to the modulating crossflow. The pressure of the chamber is up to 3.5 atm and the corresponding Weber number is up to 510. The spray of a liquid jet for steady and oscillating crossflow is characterized. The flow field at the injector location in the crossflow direction is determined using PIV (Particle Image Velocimetry) for oscillating as well as steady crossflow case. Planar Mie-scattering measurement is used to characterize the response of spray formed under oscillating crossflow and supplementary phase-averaged PDPA measurements are used to understand the response behavior. The global response of spray to the oscillating crossflow is characterized using the planar Mie-scattering imaging. It shows that there exist very little differences in the heights of the maximum-pixel intensity trajectory for the non-oscillating and oscillating crossflow conditions and the trajectory under oscillating crossflow is lower than that of steady crossflow, suggesting the oscillating crossflow affects the atomization (i.e. the oscillating crossflow enhances atomization process, results in smaller droplets and penetrates less transversely). The response of spray to the oscillating crossflow characterized in terms of the spray transfer function (STF) shows that the gain of the STF increases linearly (at least monotonically) as the liquid-air momentum flux ratio increases but does not change as much with respect to the change of the Weber number for a fixed liquid-air momentum flux ratio. This also indicates that the liquid jet atomization under oscillating crossflow is enhanced much more with the increase of liquid-air momentum flux ratio than with the increase of Weber number. The phase-averaged PDPA measurements confirm that the oscillating crossflow indeed enhances the atomization process in that the oscillating crossflow results in relatively greater number of smaller droplets and the mean droplet size.