1. Introduction
A major new extension of the capabilities of FLOW-3D® — the multi-block grid model — has been incorporated into the code starting with Version 8.0. Multi-block gridding in FLOW-3D® will enable more efficient use of the software’s resources when modeling complex flow phenomena. Each block spans a certain region of the whole flow domain and contains the standard structured rectangular mesh. Two types of mesh blocks can be used: the nested blocks and the linked blocks.
Data transfer between any two mesh blocks is facilitated by special boundary (or ghost) cells. Solution quantities are interpolated from the real cells of a donor block into the boundary cells of the acceptor block. The interpolation technique varies depending on the variable at hand. Conserved quantities, like concentrations and thermal energy, are interpolated using the piecewise constant method. A special variant of this method is used for fluid fraction interpolation, where a reconstruction of the interface is performed to locate the interface within the donor cells before the interpolation.
Pressure and velocities are calculated using linear interpolation to preserve the gradients. A mixture of the Neumann- and Dirichlet-type boundary conditions is used for the solution of the Poisson equation for pressure. A weighing factor defines the contribution of each type of the boundary condition to the final solution, ensuring continuity of both pressure and velocities across the inter-block boundaries, convergence and local conservation of mass.