FLOWCast UNIT 16: Flow Simulation Strategies
FLOWCast is a true fluid flow simulation package and may involve some strategies or methods somewhat different than those used in traditional solidification modeling.
First of all, the full flow simulation mode is very calculation-intensive. This means that it takes a lot of computer processing power and memory to be able to run. We recommend that you use the fastest computer processor and the most amount of RAM memory that your budget will allow. We also recommend that you use the largest node size, or the smallest number of nodes, that you can reasonably use for a given model. The amount of processing time increases more than proportionally as the number of nodes increases.
In many cases the quick mode of FLOWCast will allow you to do a good job of simulating the filling and progressive heat loss of the metal entering the mold cavity.
Even though the quick mode is not a full CFD simulation, it still is very useful in approximating mold filling and the temperature distribution within the liquid metal.
In the full flow mode, FLOWCast has some internal limits (both high and low) on the entering velocity of the liquid metal. FLOWCast determines this velocity based on the Fill Time (in seconds) that you enter for the model. Knowing the volume of the mold cavity, FLOWCast calculates a flow rate from this fill time, and then calculates a velocity based on the area of the entering liquid. The area of the entering liquid is the contact area between the Fill Material and the Casting Material (or Riser Material).
FLOWCast will inform you if the velocity is too high or too low. In each case, you can do the following:
- If the velocity is too low, you can decrease the Fill Time or decrease the contact area of the Fill Material.
- If the velocity is too high, you can increase the Fill Time or increase the contact area of the Fill Material.
FLOWCast can automatically adjust the Fill Time for you, or you can exit from FLOWCast, make a change and then re-mesh the model.
In future versions we intend to release fill time calculations based on casting size and shape.
If the RAM memory on your computer is limited, you may receive a message when you start FLOWCast saying that the simulation cannot be run for that model due to not having enough available memory. It is possible in this case that you can run a simulation in quick mode (click on the hourglass tool to change to quick mode) but you will not be able to run FLOWCast in full simulation mode unless more memory is made available. Sometimes this may mean shutting down other programs that are operating, or sometimes this may mean installing more RAM memory in the computer.
In using the SOLIDCast mold filling calculation, with complex gating systems (i.e., multiple gates from a common runner system) our recommendation was normally to make the entire gating system of Fill Material so that even distribution of flow from all the gates could occur. This is no longer necessary with FLOWCast (including both the quick and full algorithms). With FLOWCast, you can create the entire gating system using either Casting Material or Riser Material, and place the Fill Material at the point of entry of the molten metal (typically, at the top of the sprue). FLOWCast does a good job of apportioning flow through a gating system on a realistic basis.
For simulations with a high number of nodes, the output files created by FLOWCast can become very large, especially if small steps are specified for saving the results.
For example, with a simulation of 1.6 million nodes and time steps set at 1%, we have found result data files up to 2 GB in size. This can be reduced by increasing the saving increment. In most simulations, what happens initially as the metal enters the casting is of interest, and you may want to capture this in small increments of say 1%.
However, as the casting fills the incremental changes are not as great. It is possible to stop the FLOWCast simulation part way through and change the percent increment for saving data (say, from 1% to 5%) and then proceed with the rest of the simulation. When you animate this simulation or create an AVI file, you will see the initial steps at 1% and then the 5% increments afterward. This can significantly reduce the disk space needed for result data files.
You can delete the FLOWCast result files from within SOLIDCast by highlighting the mesh name on the project tree, then selecting File Remove FLOWCast Data …
Or, you can delete the mesh and the associated FLOWCast data will be deleted as well. It is recommended that after generating all of your output reports, you either delete these files or archive them on other media to avoid filling up your hard drive.
If you are running tilt-pour permanent mold simulations, keep in mind that in FLOWCast only the full mode can be run for tilt-pour simulations. The options therefore are to run the full FLOWCast fill simulation or the traditional SOLIDCast filling simulation for the warm-up cycles. For maximum speed of the initial cycles, you can choose the SOLIDCast fill simulation for the warm-up cycles and then choose FLOWCast full simulation for the final cycle.
FLOWCast assumes that the mold is well vented, i.e., that the pressure on the advancing liquid is always atmospheric. Later versions will incorporate consideration of gas pressure and vacuum conditions.