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.