Problem in running solution: the residual values goes higher

Hi All,

I am running a case of natural ventilation study of a building (9x8x3.5m) with the window (top hung window) open. I run the case as an outdoor study, the refinement level of the Butterfly geometry is set to 1,4.

The wind tunnel data already fulfils the requirement of a < 3% blockage ratio. I use a gradient tunnel for the block mesh with a cell size of 0.2. As for the snappy hex mesh setting, I tried different settings to reach the maximum orthogonality < 60. However, when checking the result of the snappy hex mesh in Paraview, I am still not sure if the result is good enough to produce a reliable result (picture attached). Honestly, I am new to CFD thus, I haven’t had enough understanding about CFD, Butterfly, and all the settings, especially in the snappy hex mesh.

Another problem arose when I tried to run the solution. At first, I set the maximum iteration to 850. Yet, by the end of 850 iterations, the residual value only reached 0.00022. Then I add the max iteration to 2000 as I intend to reach a lower residual value (I read that to produce a reliable result, the residual value should be at least 1 e-5). After I add the number of iterations, the residual value goes down but only until reaches 0,00017 at around iteration 930, then the values keep increasing. I have no idea what happens. Is it the problem with my geometry, or the problem in my snappy hex mesh setting? I want to upload the residual plot, but I am not successful yet in plotting it. Idk why.

Could someone please help or share any thoughts so that I could run this case successfully?

Thank you very much in advance.


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