A dynamic subfilter-scale stress model for Large eddy simulations

In conventional large eddy simulation, the filter width is related to the grid size; this decouples the filter width from turbulence physics and results in unwanted dependence of the subfilter model on the grid arrangement. Relating the filter width to the integral length-scale is a potential solution. We proposed an approximation for the integral length-scale, in which a single model parameter was determined based on the global contribution of unresolved (subfilter) scales to the resolved ones denoted as subfilter activity (Piomelli \& Geurts, \textit{Direct and Large-Eddy Simulation VIII}, pp. 15-20, 2011). We have devolped a localized model in which we assign a target value to subfilter activity locally, requiring the model parameter to adapt itself to the local state of the flow. This dynamic modification is coupled with a local formulation for the integral scale. The modified model was applied on channel flow at $Re_\tau$ up to $2,000$, accelerating boundary layer and backward-facing step flow at high $Re$ with comparable accuracy as the Dynamic Smagorinsky model but with less computational expense.