Mixing Characteristics of Non-Newtonian Impinging Jets at Elevated Pressures

The effect of chamber pressure on the mixing characteristics of like-doublet impinging liquid jets is experimentally and numerically investigated for non-gelled and gelled hypergolic propellant simulants. The experiment uses planar laser induced fluorescence technique to investigate the mixing efficiencies of impinging liquid streams. It is found that mixing is enhanced for both gelled and non-gelled fluids as the pressure increases. However, gelled simulants generally result in poorer mixing as compared to their non-gelled counterparts, suggesting that pre-impingement conditions are important factors that determine mixing efficiency. To verify this hypothesis, high-fidelity direct numerical simulations, based on a state-of-the-art volume-of-fluid (VOF) method are conducted at elevated pressures for the gelled simulant, treated as a Herschel-Bulkley non-Newtonian fluid. It is found that the Sauter mean diameter (SMD) changes significantly, and approaches the SMD of non-gelled impinging jets if the incoming jets are either perturbed by a sinusoidal disturbance or a fully developed turbulent flow profile is introduced, explaining the experimental observations and confirming the hypothesis.