Hello!
Im doing cooling sims for my FSAE teams accumulator and I have been simming values with varying fan CFMs and now ran a sim with no fans at all to validate the presence of the fans. The run finished and I found that the cells were not as hot as they should be. I set the heat rate of each of the cells to reach 60 celcius through the run and with no air inlet into the segment section I would have expected each of the cells to reach 60 celcius but that is not the case. Feel free to look at my previous sims at 24cfm and lower with the fan inlet in the boundary conditions.
Please let me know if you need furthur clarification on what Im asking or more details about the paramaters as a whole.
Taking a look at your project, I have a few comments.
Firstly, the ‘fan’ setup in your model seems to be oriented unintuitively considering its purpose. Are you sure it should be facing in negative z direction? Normally, the fan would be designed to get the air out from the domain below and then into the upper portion of the model (+z axis direction).
Secondly, the fans are modeled with incorrect velocity inlet and pressure outlet BCs. This is usually tricky when you are not modeling the fan with a momentum source but are assigning boundary conditions to the flow region faces directly. To imagine it better, it would help to picture the fan’s effect from the flow region perspective. When you assign velocity inlet to a face in a direction outwards of the flow region, it is effectively not a working boundary condition. The pressure outlet at the other end of this ‘fan’ has nothing to do with the velocity inlet mentioned before because there is only void between the two faces. These boundary conditions therefore adversely affect the simulation’s results. It might make more sense to have the same flow rate or velocity as boundary condition at both the ends of the fan in the same direction. For example, velocity inlet and outlet with same speed / flow rate and same direction (most likely in +z direction).
The case without the fan therefore cannot be compared at the moment to the case with the fans, because the physics does not really make sense in the initial case. Also, the run (without fans) was unfinished because of maximum runtime. Although the residuals seem to be going in the right direction, since it is an unfinished run with slightly higher residuals AND since there is no point of comparison with the other studies because of points 1 and 2, it is difficult to state the correctness of the results at this stage. The meshing is pretty fine overall (in numbers) but most of the inlet outlet faces (cross sections) have very few cells and this might also be a reason for some unreal results.
Hope that answers your question! Let us know how it works out for you!
