Abstract
The Linear Eddy Model (LEM) is formulated to capture affordably the distinction between turbulent convection (stirring), molecular diffusion, and chemical reaction in turbulent reactive flows. This is achieved by reducing the description of scalar fields to one spatial dimension. We here present a formulation of LEM in 3 dimensions, which incorporates three orthogonally intersecting arrays of 1 D LEM domains. In LEM3D advection is accounted for by Lagrangian coupling of the domains. LEM3D has been implemented in a computer code, and is presented conceptually as in detailed operational algorithms. The LEM3D geometrical substructure is constructed to be used as a subgrid scalar closure either for RANS or LES applications. As a substructure for a global flow solver, LEM3D provides small-scale resolution in all three spatial directions of a turbulent flow field. In this report we give a full description of the coupling of LEM3D to the RANS approach to turbulence modelling. The preliminary goal of this work has been to extend the applicability of the in-house SPIDER code at SINTEF and NTNU, based on the RANS equations for solving the turbulent flow field and the EDC combustion model for solving the chemistry. The LEM3D substructure is expected to complement the capabilities of RANS by adding unsteadiness and resolving flame structure. The coupled LEM3D-RANS model represents a novel approach to high-fidelity resolution of turbulence-chemistry interactions in turbulent combustion. This modelling approach has the potential of resolving the smallest scales of reactive flows at a computationally affordable cost compared to a corresponding Direct Numerical Simulation (DNS)