A large eddy Simulation based on the diffusion‐velocity method and the discrete vortex method is presented. The vorticity‐based and eddy viscosity type subgrid scale model simulating the enstrophy transfer between the large and small scale appears as a convective term in the diffusion‐velocity formulation. The methodology has been tested on a spatially growing mixing layer using the two‐dimensional vortex‐in‐cell method and the Smagorinsky subgrid scale model. The effects on the vorticity contours, momemtum thickness, mean streamwise velocity profiles, root‐mean‐square velocity and vorticity fluctuations and negative cross‐stream correlation are discussed. Comparison is made with experiment and numerical work where diffusion is simulated using random walk. Copyright © 2004 John Wiley & Sons, Ltd.

SUMMARYA large eddy simulation based on ÿltered vorticity transport equation has been coupled with ÿltered probability density function transport equation for scalar ÿeld, to predict the velocity and passive scalar ÿelds. The ÿltered vorticity transport has been formulated using di usion-velocity method and then solved using the vortex method. The methodology has been tested on a spatially growing mixing layer using the two-dimensional vortex-in-cell method in conjunction with both Smagorinsky and dynamic eddy viscosity subgrid scale models for an anisotropic ow. The transport equation for ÿltered probability density function is solved using the Lagrangian Monte-Carlo method. The unresolved subgrid scale convective term in ÿltered density function transport is modelled using the gradient di usion model. The unresolved subgrid scale mixing term is modelled using the modiÿed Curl model. The e ects of subgrid scale models on the vorticity contours, mean streamwise velocity proÿles, root-mean-square velocity and vorticity uctuations proÿles and negative cross-stream correlations are discussed. Also the characteristics of the passive scalar, i.e. mean concentration proÿles, root-mean-square concentration uctuations proÿles and ÿltered probability density function are presented and compared with previous experimental and numerical works. The sensitivity of the results to the Schmidt number, constant in mixing frequency and in ow boundary conditions are discussed.

A phenomenological model simulating stratification of temperature and species concentration was developed to predict engine misfire. The model incorporates the coalescence dispersion model for finite rate mixing and the mass entrainment model for flame propagation. The fuel mixture in the combustion chamber is divided into equal mass particles, each having a thermodynamic state. A first order chemical rate reaction for the combustion of propane in air is used. A set of ordinary differential equations for the evolution of temperature and species concentration for each particle is formulated. A predictor corrector method was developed to solve the system of equations.The model was tested extensively for the ignition limit. The effect of turbulence intensity, intake temperature. equivalence ratio and spark advance were investigated. An optimum level of turbulence intensity that enhances burn rate was observed. Increasing the intake temperature allows a higher optimum value of turbulence. Varying the spark advance combines the effect of intake temperature and turbulence intensity. When the spark advance is retarded, leaner mixture can be used.

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