Surface Instability on Cryogenic Swirl Flow at Sub- to Supercritical Conditions

Abstract

An experimental investigation was conducted to discover the characteristics of a cryogenic swirl flow at subcritical to supercritical conditions. In the experiment, liquid nitrogen was injected into a high-pressure chamber through an open-type simplex swirl injector. The flow was imaged by high-speed photography, and the instability frequency was measured by the laser beam diagnostics of the flow. Comparing the flow images of the cryogenic and conventional swirl flows, different behaviors were noted, and it was hypothesized that the instability of the cryogenic swirl flow was dominated by the precessing vortex core in the central toroidal recirculation zone. When the ambient condition of the flow was changed from subcritical to supercritical, the phase change and subsequent density change of the injectant differed, and flow actions, such as the behavior of the downstream flow, the spray angle, the wavelength, and the propagation velocity, changed drastically. When measuring the frequency of the flow instability, it was found to correspond to that of the precessing vortex core instability. The frequency decreased with the ambient pressure due to the decreasing flow velocity, but it did not change drastically when the surrounding conditions changed from subcritical to supercritical. This implies that the interface of the flow is highly affected by the density of the phase-changed injectant, but that the instability of the flow is determined by the flow in a liquid state.