Injection of cryogenic fluids into a supercritical environment is at present encountered in cryogenic rocket engines and in several upcoming novel environment friendly technologies such as the Recuperated Split Cycle Engine, Liquid Air/Cryogenic Energy Storage etc. However, the peculiar characteristics and ambiguous behaviour exhibited by cryogenic fluids in supercritical environment that has baffled the scientific community till date indicates that a thorough knowledge on the underlying mechanisms is still lacking. For example, the ambiguous behaviour of the injected cryogenic fluid behaving as liquid-like sprays and gas-like jets in different super critical environments is one such example. Furthermore, the continuously varying thermodynamic and mechanical properties of the fluid around its critical point leads to complex interdependent thermo-mechanical interactions which significantly affects their flow dynamics as well. These thermo-mechanical interactions also give rise to some unique thermophysical mechanisms such as density stratifications and heat shields that alters the mixing and turbulence characteristics of such cryogenic sprays/jets. As a result, cryogenic fluids injected into a supercritical environment are affected by various colliding factors that are impossible to evaluate manually, thereby requiring the use of computational solutions for an accurate prediction. The overarching aim of the research is to assemble a computational fluid dynamics framework (namely ‘coolFoam’) capable of accurate numerical simulations of cryogenic fluid injection into supercritical environment. This is achieved through the examination of experimental results, identification of a suitable numerical model to estimate the fluid properties and a thorough investigation of the underlying thermo-mechanical dynamics that drives the injected cryogenic fluid evolution. An adaptable model that applies surface tension to liquid phase and diffusion to supercritical phase is also pursued to include the surface tension and diffusion effects that are usually omitted in similar research on cryogenic and/or supercritical fluids. The examination of previous subcritical and supercritical cryogenic injection experimental results and the assessment of their primary breakup in this research has conclusively proved that the subcritical cryogenic injection predominantly obeys the primary breakup/atomisation regime classification in contrast to the supercritical injection that entirely defies it. In addition, the constitution of the involved fluids in a single-specie versus multi-specie is revealed to be the main condition for the observed gas-like jet or liquid-like spray characteristics at supercritical pressures. With respect to the thermo-mechanical dynamics, the suspected predominant thermodynamic influence and kinematic independence of the cryogenic jet characteristics in a supercritical environment is proven through numerical simulations in the ‘coolFoam’ framework. Furthermore the 3-dimensional aspect of the density stratification acting like solid tubes is revealed for the first time in detail thereby giving dynamic insight of their role in instability suppression. The inspection of kinematic properties of the supercritical cryogenic jets unravels its characteristic similarity to gaseous jets over liquid sprays and is an important development towards understanding the ambiguous jet/spray characteristics observed. The numerical simulations of single-specie and multi-specie configuration of cryogenic liquid injection with the aid of the further enhanced ‘coolFoam’ with adaptive surface tension and diffusion concludes that the role of surface tension is negligible in the case of injection of cryogenic liquids close to the critical point in both configurations and suggests a diminished influence in the case of liquid injection in a single-specie configuration. However, there are indications of high surface tension delaying the thermodynamic decay of fluid parcels while accelerating the breakup of the liquid column. In addition, the numerical simulations of low-temperature and near-critical liquid injection into supercritical environment has revealed for the first time that in contrast to the injected fluid undergoing a predominantly thermal decay in the case of near-critical injection, in the case of low-temperature liquid injection the injected fluid undergoes a mechanical decay that is augmented by thermal decay thereby resulting in much more rapid decay/disintegration of the jet.
|Date of Award||May 2023|
|Supervisor||Konstantina Vogiatzaki (Supervisor), Robert Morgan (Supervisor) & Guillaume De Sercey (Supervisor)|