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Residual Divergence Issue In Convective Fan Cooling Simulation |
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February 27, 2020, 20:03 |
Residual Divergence Issue In Convective Fan Cooling Simulation
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Hello everybody, I hope you're having a great day.
Overview: I am running a simulation in STARCCM+ to determine if fan cooling will be powerful enough to cool an electric car battery. The battery and two fans are contained in a case with room for air to flow around the battery. Holes are on either side of the case act as inlets and outlets (real world inlets and outlets as opposed to those set up in the regions portion of the simulation) for air to flow in the z-direction. The whole case, battery and fans are contained in a larger fluid volume. Mesh: I am using surface mesher, polyhedral mesher, and prism layer mesher. A custom control has increased mesh resolution to a fixed 1.5 mm within the battery case and the cells grow outside the case towards the boundaries of the encasing fluid region. 8.5 million cells in total. Cell skewness is less than .5. Cell quality could stand to be improved. There are a handful (200 or so) of particularly bad cells near the fan blades. Physics: I am running 3D, steady, coupled energy, coupled flow, constant density, and K-e turbulence. Regions: There is a main fluid region that was made by subtracting the case, batteries, and fans from a block. I've set heat flux generated on the surface of the batteries equal 1200 W/m^2K. Two rotating regions are contained within the large fluid region that are located around the fan blades. They are set to 5500 rpm. I have stagnation inlets and pressure outlets on all three regions and there are interfaces between the fluid region and the rotating regions. My Problem: I run the solution and it looks good until the 33rd iteration and then the turbulent kinetic energy, z-momentum, and turbulent dissipation rate residuals spike up drastically and stay up for 3000 more iterations at which point, the solution is cancelled. The temperature on the batteries never settles at a fixed value. I'm not sure what is causing the solution to diverge and any insight would be GREATLY appreciated. It may just be that I need to really work on the mesh some more but I have a feeling its the physics models since I've never worked with turbulence before. If it is the mesh, is there any way I can correlate which cells are causing the residuals to spike at 33 iterations in? Thank you so much for your replies. Let me know if you need any more information! |
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