Liquid-fuel droplet vaporization and cluster behavior at supercritical conditions.

摘要

A systematic investigation of supercritical droplet vaporization and droplet cluster behavior has been conducted, and the research work addresses a variety of fundamental issues related to droplet vaporization and dynamics at typical conditions of liquid-propellant rocket combustion devices. A unified treatment of real-fluid thermodynamics has been developed based on fundamental theories. Special attention was given to the thermodynamic non-ideality and transport anomaly in the transcritical regime. A modified Soave-Redlich-Kwong (SRK) equation of state was utilized to derive all the thermodynamic correlations, which were then incorporated into the numerical scheme to enhance numerical efficiency and robustness. A preconditioning scheme with the dual time-stepping integration technique was implemented to render the numerical algorithm capable of treating low Mach-number fluid flows.; A series of calculations was performed to examine the cluster behavior of liquid oxygen (LOX) droplets in both sub- and super-critical hydrogen environments. The hydrogen density plays a decisive role in determining droplet interactions through its influence on the temperature and mass fraction gradients at the LOX droplet surface. In the later stage of the vaporization process, droplet vaporization rate is dominated by the oxygen accumulation at the droplet surface.; Much effort was expended to explore LOX droplet vaporization in forced-convection environments. A dimensionless parameter We1/2/ Oh, which represents the ratio of aerodynamic and viscous forces, is found to be the major factor determining the droplet deformation under supercritical conditions. Results of droplet lifetime are well correlated as a function of the initial Reynolds number and pressure. A linear relationship is generated for droplet velocity.; The interactions with two droplets moving in tandem in supercritical convective environments have been investigated. Results indicate that droplet dynamics exhibits characteristics distinct from that of an isolated droplet. A forward bag break-up of the leading droplet was found when the two droplets are initially positioned closely with a H/R ratio (the ratio of the initial droplet spacing to droplet radius) of 4 and a pressure of 100 atm. Forward movement was observed for the trailing droplet under the same condition. Increase of pressure weakens droplet interactions.