A CFD Methodology for Liquid Jet Breakup and Vaporization Predictions of Compressible Flows

Abstract

A robust computational fluid dynamics methodology for simulating liquid jet discharge and breakup in high-speed gas/liquid flows is being developed for use in practical engineering applications. The proposed approach is cast within a RANS framework and utilizes a volume-of-fluid type (VOF) methodology to efficiently capture the gas/liquid interface location. Relevant physics are modeled to predict liquid atomization/vaporization through a cascading process involving interface surface breakup, primary droplet formation, and droplet secondary breakup and vaporization. The current VOF approach is well suited for applications involving liquid jet discharge at lower ambient pressures, such as liquid fuel venting, gas-turbine fuel injection, or atmospheric bulk-dispense problems, where the liquid behavior is essentially incompressible making the numerical solution more difficult in a compressible flow environment. In place of a traditional VOF approach with different thermodynamic treatments of gas and liquid, a unified, multi-phase thermodynamic framework is used which is applicable to both the gas and liquid phases. Density-based fluid dynamic equations are transformed to a “quasi-pressure-based” form, and preconditioning is used which facilitates integrating the equations with widely disparate sound speeds. This approach is implemented in the structured grid code CRAFT CFD, as well as the multi-element unstructured grid code, CRUNCH CFD, permitting grid adaptation to be applied to enhance efficient gas-liquid interface tracking. In order to avoid resolving the liquid surface breakup numerically, a surface breakup model is applied with correlations for droplet formation based on local shear and surface tension across the gas/liquid interface, allowing the size of the droplets generated to vary spatially as well as in time with the local evolution of the gas/liquid interface. These primary droplets are transferred to an Eulerian dispersed phase where they are subject to secondary breakup and vaporization. Several solutions of exemplary problems are presented.