Swirl coaxial injectors are widely used to achieve efficient mixing and combustion in many propulsion and power-generation systems.These engines operate at pressures much higher than the critical pressures of the injected propellants,leading to extremely complex physical phenomena and therefore imposing severe challenges to experiments.A numerical study is carried out to investigate the mixing and atomization characteristics of liquid oxygen(LOX)/kerosene swirl coaxial injectors at supercritical conditions.The formulation is based on full conservation laws and accommodates real-fluid thermodynamics and transport theories over the entire range of fluid states.Turbulence closure is achieved using a large eddy simulation technique.A grid independence study was first conducted to ensure appropriate numerical resolution and accurate flow physics.At supercritical conditions,the classic liquid-film breakup process at subcritical conditions is replaced by turbulent mixing and diffusion.Various geometric parameters,including the recess length,LOX post thickness,and kerosene annulus passage,are examined to explore their influence on mixing efficiency and flow dynamics.The recess region enhances the interaction of LOX and kerosene and thus improves the mixing efficiency.A larger post thickness results in a higher spreading angle of the LOX film and intersects the kerosene film,thereby facilitating mixing in the recess region.The width of the kerosene annulus passage significantly affects the flow evolution; a large passage increases the spreading angle of the liquid film and advances the center-recirculating zone to an upstream location.An appropriate selection of the post thickness,recess length,and annulus width must be carefully considered for optimum injector performance.The present study provides important information for injector design and underlying flow physics.