Using Grid OverlaysSometimes I have a problem that requires initial or boundary data that is determined by a much larger problem region than I can easily model. Is there a way to do such problems?
One simple way to handle many problems such as are described is to use FLOW-3D's grid-overlay restart option. This powerful technique allows a user to restart a problem using data from a previous simulation. The new problem can have an grid that may be either more coarse or more fine than the previous computation. More important, the grid in the new problem need only overlap the previous computational grid in selected regions. At the start of a new computation that using restart data, FLOW-3D will automatically interpolate the restart data onto the new grid wherever the old and new grids overlap.
A special case is the grid-overlay (GO) boundary condition in which the restart data is used to set boundary conditions on any boundary that is specified to be a GO boundary. In this case, the boundary data is considered constant (i.e., time independent) during the new computation.
Grid overlays can be used in many ways. For example, a section of a complex river flow could be coarsely modeled and then used as input conditions for a more detailed, local model of inflow conditions to a power station. Another example is the flow of a jet of liquid into a pool of liquid. A first computation of the flow could be done to obtain reasonably steady flow conditions. The results of this computation can then be used to provide initial data for more detailed computations of just the region near the jet-pool intersection where air entrainment processes might be investigated.
The ability to incorporate results from an earlier computation into a new one is a powerful modeling tool. And because of the simplicity of the procedure, users should make this as a standard part of their modeling repertoire.