Flow Dynamics of a Dodecane Jet in Oxygen Crossflow at Supercritical Pressures

Abstract

In advanced aeropropulsion engines, liquid fuel is often injected into the combustor at supercritical pressures, where flow dynamics are distinct from the subcritical counterpart. Large-eddy simulation, combined with real-fluid thermodynamics and transport processes of a liquid N-dodecane jet in oxygen crossflow, is presented at different supercritical pressures and jet-to-crossflow momentum flux ratios (J). Various vortical structures are discussed in detail. The results show that, with the same velocity ratio of 0.75, the upstream shear layer (USL) is absolutely unstable at high supercritical pressure (J=7.1) and convectively unstable at low supercritical pressure (J=13.2), consistent with the empirical criterion at subcritical pressures (Jcr≈10). While decreasing J to 7.1 at low supercritical pressure, however, the USL remains convectively unstable, manifested by the variable dominant Strouhal number of the USL along the upstream jet trajectory. Such abnormal behavior can be attributed to the real-fluid effect induced by strong density stratification at low supercritical pressure, under which an inflection point in the upstream mixing layer renders a large density gradient and tends to stabilize the USL. Linear stability analysis further verifies these findings. The analysis of spatial mixing deficiencies reveals that the mixing efficiency is enhanced at a higher J.