An Improved Ejecta Production Model Based on Richtmyer-Meshkov Instability Spike Dynamics

The FLAG Lagrange/ALE hydrocode employs a subgrid model of mass ejection as a Richtmyer-Meshkov instability (RMI), including (1) a description of RMI spike and bubble growth rates to due to Buttler et al. [W. T. Buttler et al., J. Fluid Mech, 703, 2012, pp. 60-84], (2) the Self-Similar Velocity Distribution (SSVD) model of the velocity field within a spike (in the fluid frame) as varying linearly from zero at the base to a maximum value at the tip [J. E. Hammerberg et al., AIP Conference Proceedings 1979, 080006 (2018)], and (3) a model of spike breakup. In this work, we improve on model (2) by accounting for inflow of matter at the base of the spike. This allows us to self-consistently reconcile the evolving shape of the spikes (elongation and thinning) with the inflow, and with the corresponding properties of the bubbles, under the assumption of incompressibility. Since the model enables the description of the motion of a fluid element into and along the spike, a more realistic prediction of the velocities and sizes of the resulting ejecta can result. We describe the new self-consistent model and its implementation in FLAG, and indicate how it will be coupled to the breakup model to predict sizes and speeds of the resulting particles.