Global stability analysis of jets in crossflow at supercritical pressures

Fuel injection at supercritical pressures is typical of advanced propulsion engines. Jet instabilities influence nearfield vorticity formation, which in turn affects downstream mixing efficiency and combustion instabilities. The stability of jets in crossflow (JICF) at supercritical pressures is investigated using tri-global linear stability analysis based on a novel algorithm capable of incorporating real-fluid effects. The implicitly restarted Arnoldi iteration method is employed, combined with the time-stepping method. Simulations are conducted at jet Reynolds numbers of around 2000. The GLSA results effectively capture the intricate upstream shear layer (USL) instabilities, with characteristic Strouhal numbers consistent with the results of power spectral density analysis and proper orthogonal decomposition. With a same jet-tocrossflow velocity ratio of 0.75, the jet’s USL exhibits absolute instability at a high supercritical pressure (momentum flux ratio J = 7.1), where the eigenmode originates near the nozzle exit. At a low supercritical pressure (J = 13.2), convective instability occurs, with the eigenmode emerging farther downstream. The reduction in ambient pressure increases the density ratio, amplifying the Rayleigh–Taylor instability in the USL. This results in the formation of subharmonics in the jet's downstream region and enhances local mixing. When J decreases to 7.1 at a low supercritical pressure, the USL remains convectively unstable, contradicting the empirical criterion for subcritical pressures (Jcr ≈ 10). This anomaly arises from the strong density stratification induced by intensified real-fluid effects, which may also lead to the suppression of subharmonics.