A phase change model for the simulation of cavitating droplet aerobreakup using interface-capturing schemes

Abstract

Interface-capturing schemes are well established for multi-component, immiscible flows, but
simulating phase changing flows is yet a challenge. For an N-component system including reacting
liquid and vapor states of one of the materials, we adopt the so-called six-equation model with source
terms that account for mechanical, thermal, and chemical disequilibrium furnished with an infinitely
fast relaxation procedure [1]. We solve the governing equations with our validated, GPU-enabled,
open-source, high-order-accurate flow solver called MFC [2], in which the relaxation process towards
equilibrium is simplified, for fluids obeying the stiffened gas equation of state, to finding the roots of
a 2 × 2 system of nonlinear equations.

Numerical experiments have been performed for a variety of test cases, and agreed well with previous
work [1], but there are still challenging simulations of interest in academia and industry, such as
single bubble dynamics and aero-droplet breakup problems in which phase change plays an important
role. For the latter, recent literature has shown that, when subject to a sufficiently strong shock,
internally reflected rarefaction waves can focus and induce cavitation [3]. We managed to reproduce
this behavior, generating vapor at the focal point, but the results are yet preliminary and better criteria
for both triggering the model and sustaining the newly generated mixture region must be established,
since the results depend on the sensibility of the current criteria. Additionally, phase change was
observed at locations that are known not to happen.

Therefore, in this presentation we intend to discuss modifications to our model so it can capture and
sustain phase change at the expected locations, in accordance with both theoretical and experimental
observations. We will focus on presenting results for droplet aerobreakup problems with induced
cavitation.

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