Numerical simulations of a multiphase, partially burnt fuel jet in a supersonic crossflow

We present results from detailed 3D numerical simulations of a multiphase jet comprising gaseous burnt products and seeded with unburnt fuel particles encountering a supersonic cross flow of air. This problem is of relevance to divert attitude control thrusters used in hypersonic vehicles, as well as in scramjets and detonation engines. In our simulations, the jet consists of a preheated carrier gas of burnt products and mono dispersed 20μ𝑚, 𝑛 − 𝐷𝑜𝑑𝑒𝑐𝑎𝑛𝑒 droplets. The simulations were performed using FLASH, an Eulerian shock physics code, with detailed accounting for multiphase effects including droplet deformation, breakup, and evaporation as described in Musick et al. [1]. The simulations were analyzed using a novel, jet-based coordinate system, which enables the comparison of key quantities of interest with a canonical self-similar jet used as a reference. We find that as the high-pressure jet enters the cross flow, it expands while the droplets reach a Weber number of ~300, initiating breakup. Within a downstream distance of 7 jet diameters, more than ~ 90% of the droplets break up into child droplets. These droplets achieve a velocity close to the gas flow velocity, while the Weber number drops below the critical Weber number (𝑊𝑒_𝑐𝑟𝑖 = 12 ) needed for further breakup. Heat transfer from the hot carrier gas was observed, which resulted in droplet evaporation. At a downstream distance of 15 jet diameters, nearly 70% of the total injected liquid mass had evaporated. As the cross flow comprised of pure 𝑂₂ entrained into the jet mixture, the evaporated fuel ignited, resulting in product formation.

[1] B. J. Musick et al., Combust. Flame, Suppl. vol. 257 (2023)