Large-eddy simulation on unstructured deforming meshes: towards reciprocating IC engines

A variable explicit/implicit characteristics-based advection scheme that is second-order accurate in space and time has been developed recently for unstructured deforming meshes (O'Rourke PJ, Sahota MS. A variable explicit/implicit numerical method for calculating advection on unstructured meshes, J Comput Phys 1998;142:312-45), To explore the suitability of this methodology for large-eddy simulation (LES) in reciprocating internal combustion engines, three subgrid-scale turbulence models,have been implemented: a constant-coefficient Smagorinsky model, a dynamic Smagorinsky model for flows having one or more directions of statistical homogeneity, and a Lagrangian dynamic Smagorinsky model for flows having no spatial or temporal homogeneity (Meneveau C, Lund TS, Cabot WH. A Lagrangian dynamic subgrid-scale model of turbulence, J Fluid Mech 1996;319:353-85). Quantitative results are presented for three canonical flows (decaying homogeneous isotropic turbulence, non-solenoidal linear strains of homogeneous turbulence, planar channel flow) and for a simplified piston-cylinder assembly with moving piston and fixed central valve. Computations are compared to experimental measurements, to direct-numerical simulation data, and to rapid-distortion theory where appropriate. Generally satisfactory evolution of first, second, and some higher order moments is found. Computed mean and rms velocity profiles for the piston-cylinder configuration show better agreement with measurements than Reynolds-averaged turbulence models. These results demonstrate the suitability of this methodology for engineering LES, and the feasibility of LES for computing IC engine flows. (C) 2000 Elsevier Science Ltd. All rights reserved.