Time-Filtered Navier-Stokes Approach and Emulation of Turbulence-Chemistry Interaction

This paper describes the time-filtered Navier-Stokes approach capable of capturing unsteady flow structures important for turbulent mixing and an accompanying subgrid model directly accounting for the major processes in turbulence-chemistry interaction. They have been applied to the computation of two-phase turbulent combustion occurring in a single-element lean-direct-injection combustor. Some of the preliminary results from this computational effort are presented in this paper. Nomenclature CFD computational fluid dynamics DNS direct numerical simulation LES large-eddy simulation RANS Reynolds-averaged Navier-Stokes approach URANS unsteady RANS TFNS time-filtered Navier-Stokes approach SGS subgrid scale SFC subfilter component FCP filtering-control parameter LEM linear-eddy mixing model LDI lean-direct injection VBB vortex-breakdown bubble PVC precessing-vortex core 1.0 Introduction High-fidelity simulation of liquid combustion in practical engineering devices remains an elusive target in spite of significant advances in physical models and numerical methods over the past decade. Within these devices, t here are a broad range of intricate physical and chemical phenomena, with liquid fuel atomization and spray, as well as turbulence-chemistry interaction, being two of the most important processes. The most accurate and straightforward numerical approach to fluid flow problems is to solve the Navier-Stokes equations without filtering and approximation other than numerical discretizations whose errors are to be controlled by highly accurate numerical schemes. This approach is known as the direct numerical simulation (DNS). Although the governing equations are solved directly in DNS, the use of models to accommodate the multiphase formulation and interaction is still unavoidable. Much more research in this area is needed. Modeling and simulations of fuel injection and spray combustion is a very difficult task, in fact, many existing large-eddy simulation (LES) of spray flow and combustion invoke the same liquid-phase models as those used in the traditional Reynolds-averaged Navier-Stokes (RANS)