CSAR Seminar

SPEAKER: Asghar Afshari, Michigan State University

TITLE: Large-Scale Simulations of Complex Turbulent Reacting Flows

DATE: Wednesday, August 16, 2006
TIME: 10:00 A.M.
PLACE: 2240 DCL
1304 W. Springfield Ave., Urbana, IL

ABSTRACT

A density-based, multi-block, computational model has been developed for large eddy simulation (LES) of reacting and nonreacting, single- and multi-phase, compressible turbulent flows in complex geometries and generalized coordinate systems. The spatially-filtered form of the compressible continuity, momentum, energy, and scalar equations are solved together with various subgrid turbulence closures. All spatial derivatives are approximated by a high-order compact differencing scheme and time derivatives are modeled via a low-storage, three-stage, third-order, Runge-Kutta method. The nonreacting, single-phase results for isotropic, jet, and axisymmetric sudden expansion turbulent flows are found to be in good agreement with those obtained via validated numerical methods and with the available experimental data. Effects of boundary conditions, inflow/outflow conditions, subgrid scale model, and various physical and geometrical parameters on the flow in sudden expansion are studied in detail. The simulated results indicate that the high-order compact differencing scheme is an appropriate numerical method for LES while the multi-block capability of the scheme enables its application to complex geometries.

Simulations of reacting single-phase flows are also considered. For this, a generalized Lagrangian/Eulerian, theoretical/numerical methodology is developed in which the subgrid mixing and reaction is obtained by the filtered mass density function (FMDF) methodology. The LES/FMDF method has several advantages over conventional methods and is implemented via a novel Lagrangian numerical scheme. The new Lagrangian FMDF flow solver is coupled with the high-order multi-block flow solver. This allows LES/FMDF to be extended to general coordinate systems. The consistency, convergence, and accuracy of the FMDF and the Monte Carlo solution of its equivalent, stochastic differential equations are assessed for different flows. The consistency between Eulerian and Lagrangian fields is established for non-reacting isothermal and non-isothermal flows as well as reacting flows in an axisymmetric, dump-combustor. The results show good consistency between conventional LES and FMDF method for nonreacting and reacting cases. The results obtained for turbulent reacting flow in a premixed propane-air dump-combustor show favorable agreement with laboratory data. The effects of the inlet flow and boundary conditions on the turbulence and combustion within the combustor are also investigated in details. The results of these investigations will be presented in my seminar together with the results for two-phase reacting flows.