On the performance of the joint velocity-scalar PDF method near walls

Abstract

Wall modelling of turbulent reacting flows is crucial for applications such as aero-engine simulations. The velocity-scalar probability density function (PDF) method has proven effective for modelling flames in complex combustion regimes, but its application near walls is computationally expensive due to the need for wall-resolving grids, even with the aid of adaptive mesh refinement. This study aims to reduce computational cost by employing a modern wall model in large eddy simulations (LES). We demonstrate that a simple subgrid model is sufficient for a wide range of wall distances, though modification to the stochastic forcing is needed to prevent spurious pressure formation near walls. The proposed wall-modelled stochastic fields framework significantly improves upon existing methods without wall modelling. It also highlights the potential for cost savings by using wall-modelled LES-PDF. For this purpose, the Eulerian stochastic fields framework is particularly suited as it can integrate with most existing LES wall models with minimal modifications.