The Grid Overlay procedure allows users to check the effects of grid refinement or to efficiently compute problems in which the region of interest is progressively decreasing or increasing, e.g., an explosion. For steady-state results a coarse grid might first be used to rough out a solution and then be replaced by a fine grid using the grid overlay procedure to give an accurate final answer.
Inkjet Example Using Grid Overlay
An example of the grid overlay procedure is shown in the accompanying figure of an inkjet device (left and middle). The computation started with a nozzle/piston assembly. After the jet is detached a new grid is used (right) to track its subsequent development. Additional grids can be used to follow the development of the moving jet for as long as desired. Using a grid overlay requires no special effort on the part of the user since the program does this automatically when restarting a simulation.
The grid overlay procedure is a powerful option in FLOW-3D that allows users to change the gridding of a computation while it is in progress. A new grid may be defined completely independently of the original grid. The new grid, for example, may be finer or coarser and it may overlay all or only a portion of the old grid.
Grid Overlay Boundary Conditions
One useful application of the Grid Overlay Procedure is to perform a simulation that generates a flow profile for use in another simulation as a boundary condition. For example, steady laminar or turbulent flow in a pipe can be first simulated then used to start a second simulation with the end of the pipe flow grid overlaid on the inflow grid region of a second simulation requiring this profile as an inflow boundary condition. When the second simulation is restarted from the first simulation the solver will automatically check for any grid overlay regions and do the necessary transfer of data from the first to the second grid.