Geometric Effects on Liquid Oxygen/Kerosene Bi-Swirl Injector Flow Dynamics at Supercritical Conditions

Abstract

A systematic study is carried out to investigate the flow dynamics and mixing of liquid oxygen/kerosene bi-swirl injectors at supercritical conditions. The theoretical framework is based on the full conservation laws and accommodates real fluid thermodynamics and transport theories over the entire range of fluid states. Turbulence closure is achieved using large-eddy simulation. A grid independence study was conducted to ensure appropriate numerical resolution and accurate flow physics. The liquid-film atomization and breakup processes at subcritical conditions are replaced by the turbulent mixing and diffusion processes typical at supercritical conditions. Various injector geometries, with differences in the recess region, post thickness, and kerosene annulus width, are examined to explore the influence of geometry on mixing efficiency and flow dynamics. A critical mixing line is defined to measure the mixedness of propellants. The presence of a recess region is found to advance the interaction of liquid oxygen and kerosene and improve mixing efficiency. A thicker post of the inner swirler or a wider annulus leads to a larger spreading angle of the inner liquid oxygen film and intercepts the outer kerosene film in a broader area, thereby enhancing mixing in the recess region. The flow structures in the recess region are complex, and the kerosene mass fraction decreases significantly near the post surface, which might increase the thermal load on the surface in the case of reacting flows. Appropriate selection of the post thickness, recess length, and annulus width must be carefully determined for optimum injector performance. The present study offers useful information in bi-swirl injector design and in studies of the underlying flow physics of swirl injection under supercritical conditions.