Surface tension effects on cryogenic liquid injection dynamics in supercritical environment

Abstract

The injection of cryogenic fluids into environments where the prevailing conditions are supercritical in comparison to the critical point of the injected cryogenic fluid is encountered in cryogenic rocket engines, and novel engine architectures such as the recuperated split cycle engine. The physical characteristics of cryogens injected into supercritical environment are rather unclear. While surface tension is usually assumed to be absent/negligible for supercritical fluids, recent experimental research has identified the existence of surface tension and its effects on liquid hydrocarbons in supercritical environment. This research work proposes an alternative computationally simple adaptive surface tension algorithm for the simulation of a liquid injected into supercritical environment. The numerical simulations presented here correspond to single- and binary-specie cases of iquid nitrogen and liquid methane respectively, undergoing phase transition post their injection into supercritical conditions. Following a critical review of related numerical works, this paper begins with a brief explanation of the physics behind the surface tension effect in a binary-fluid interface in which a supercritical fluid is involved and we present why this effect is of relevance to supercritical cryogenic jets? Then, the rationale and specifics of the the new modelling framework based on adaptive surface tension is discussed along with its implications. The results of the numerical simulations of low-temperature vs near-critical temperature iquid nitrogen and liquid methane injection dynamics revealed the drastically different fluid- and thermo-dynamics at play in these two cases. The role of surface tension at these conditions is also explored.