Comprehensive Study of Cryogenic Fluid Dynamics of Swirl Injectors at Supercritical Conditions

Abstract

A comprehensive study is conducted to enhance the understanding of swirl injector flow dynamics 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 of concern. Liquid oxygen at 120 K is injected into a supercritical oxygen environment at 300–600 K. Detailed three-dimensional flow structures are visualized for the first time in the pressure range of 100–200 atm. A smooth fluid transition from the compressed-liquid to light-gas state occurs, which is in contrast to a distinct interface of phase change at subcritical pressure. Dynamic behaviors of the oscillatory flowfield are explored using the spectral analysis and proper orthogonal decomposition technique. Various underlying mechanisms dictating flow evolution, including shear-layer, helical, centrifugal, and acoustic instabilities, are studied in depth. The hydrodynamic wave motions in the liquid-oxygen film are found to propagate in two different modes: one along the axial direction at the local wave speed; the other in the azimuthal direction and convected downstream at the mean flow velocity. Results show good agreement with the analytical prediction of the overall response transfer function of the swirl injector. The dominant mode of the azimuthal wave is triggered by the natural acoustic oscillation within the injector. Compared with the two-dimensional axisymmetric results, the calculated liquid-oxygen film is thicker and the spreading angle smaller due to the momentum loss and vortical dynamics in the azimuthal direction.