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The KIVA family of codes (Amsden et al., 1989,1993,1997) are being used by many researchers for internal combustion engine simulation. For these codes to continue to be useful, improvements need to be made to make them more efficient. One of the most CPU intensive parts of these codes is the pressure solver. Improvement in the convergence of the pressure solver could have a significant effect on the performance of the overall code. This paper presents the theory behind the matrix solution procedure utilized by KIVA. A different approach to preconditioning is then presented. When implemented, it is shown that the overall CPU time required to perform a simulation is reduced by up to 20% for pressure dominated three-dimensional simulations. This is accomplished without an increase in memory allocation.

The purpose of the present study is a to demonstrate and validate the use of the conserved scalar/assumed pdf approach to simulate turbulent mixing. To achieve this goal a numerical simulation of an experimental bench-mark problem is performed. A two-dimensional finite volume axisymmetric model numerically simulates the steady state passive scalar/air mixing. The computational study is conducted by solving the Reynolds Averaged Navier Stokes (RANS) flowfield governing transport equations. The turbulent fluctuations are computed by the two-equation k-e model. In addition to the flowfield variables, the model also solves for the mean and variance of the passive scalar concentration. To calculate the mean density, the probability density function (pdf) of the mixture fraction is assumed to follow the Beta-function distribution. The mean density is then computed by the convolution integral of the instantaneous density over the mixture fraction space.