Fighting Heat conduction convergence with multiple metal type
|
Conductive heat transfer containing two or more different metals (Aluminum and Steel) with tetrahedral cells (equangle skewness less than 0.7) caused severe convergence problem . I could not get that case converged and the heat transfer rate (Report --> Flux) did not balance (100% difference). Summary: 1) For Heat Conduction calculation for two or more metal taype (no convection) with tetrahedral cells : Double precision is a must. Double precision +Node based = reasonable convergence (1% imbalance) Double precision + W-cycle multigrid = Perfect convergence (0% imbalance) Double precision + W-cycle + Node-based = Perfect convergence (0% imbalance) 2) With hex cells, one may achieve reasonable convergence with 1% heat transfer imbalance without using W-cycle multigrid and/or Node based solver option. For better convergence, one must use node-based option or w-cycle multigrid Details of the tests for this case are given below. ________________________________________ The I tried double precision solver with 1st order upwind differencing scheme and this certainly somewhat helped to achieve heat transfer rate balance. However, the residual values went up to 10e-4 for energy and heat flux balance did not reach to an acceptable value (50% difference (0.95 to 0.56 ). Then I turned on the Node Based option on the Define --> Model --> Solver panel. This dramatically lowered the residual values. This led to a good heat transfer balance (from 0.56 to 0.06). Now for this case with node based and 3ddp selections, I switched to W-Multigrid (from V). This lowered the residual values even further (10e-12) and got a perfect heat transfer balance (10e-8) I have also found that if you use double precision with W cycle multigrid (with out node based option turned on), the convergence is also perfect with very good heat transfer rate balance. Node based option is not essential in this situation. I tried 3d single precision solver with W cycle (no Node based option) and the convergence is slightly better but the heat transfer imbalance is significant (dropped from 0.95 to 0.76-75%) Then I tried, 3d solver (single precision) with W-cycle and Node based option. Again, this did not help the convergence. Hence, you must use double precision solver. |
||
|