A priori analysis of subgrid-scale closures for large eddy simulation of thixotropic two-phase flows

This short communication focuses on large eddy simulation (LES) of thixotropic two-phase flows. We derive the filtered kinetic rate equation for the microstructural integrity and explicitly filter direct numerical simulations (DNS) of thixotropic jet breakup. As only one phase is non-Newtonian, we introduce a volume-fraction-based Favre-type filter to obtain a phase-consistent filtered structural parameter at the interface. Two novel subgrid-scale (SGS) terms are identified: an SGS advection of the structural parameter and an SGS contribution of the shear-induced microstructural destruction. An order of magnitude analysis reveals that both SGS contributions prevail at the gas-liquid interface compared to the liquid bulk phase. While the destruction SGS term dominates globally, both SGS terms become comparable in high-thixotropy regions. We evaluate subgrid closure models and identify promising structural models for future a posteriori LES. • A filtered kinetic rate equation for a thixotropic fluid is derived. • Two previously unexplored subgrid-scale terms are identified. • The magnitude of the subgrid-scale terms is quantified to determine their relevance. • Closure models are proposed and evaluated for both subgrid-scale terms.