Scalar Monte Carlo PDF computations of spray flames on unstructured grids with parallel computing

The article describes the extension of the scalar Monte Carlo probability density function (PDF) approach to the modeling of spray flames for application with unstructured grids and parallel computing. The solver is designed to be massively parallel and accommodates the use of an unstructured mesh with mixed elements comprised of triangular, quadrilateral, and/or tetrahedral type. The ability to perform the computations on unstructured meshes allows representation of complex geometries with relative ease. Several numerical techniques are outlined for overcoming some of the high computer time and storage limitations associated with the Monte Carlo simulation of practical combustor flows. The application of this method to a confined swirl-stabilized spray flame shows reasonable agreement with the available drop velocity measurements. The parallel performance of both the PDF and Computational Fluid Dynamics (CFD) computations has been found to be excellent but the results are mixed for the spray module, showing reasonable performance on massively parallel computers such as the Cray T3D but poor performance on workstation clusters. In order to improve the parallel performance of the spray module, two different domain decomposition strategies were developed, and the results from both strategies are summarized.