{"id":247383,"date":"2023-01-24T19:04:40","date_gmt":"2023-01-24T19:04:40","guid":{"rendered":"\/forum\/forums\/topic\/getting-back-flows-at-low-velocities-in-simulation-of-flow-through-screen-layers\/"},"modified":"2023-01-24T19:04:40","modified_gmt":"2023-01-24T19:04:40","slug":"getting-back-flows-at-low-velocities-in-simulation-of-flow-through-screen-layers","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/getting-back-flows-at-low-velocities-in-simulation-of-flow-through-screen-layers\/","title":{"rendered":"getting back flows at low velocities in simulation of flow through screen layers"},"content":{"rendered":"

Hello. I hope you are doing well.<\/p>\n

I am using the K-Omega SST model to simulate airflow through five layers of screens in fluent. The wire diameter in the screens is about 0.05mm and the distance between two consecutive wires is 0.127 mm. <\/p>\n

At low velocities (below 1m\/s) I get reverse flow at my outlet. I have a 1mm*1mm*113mm channel where the B.C.s are velocity inlet and pressure outlet at the pressure of 0 Pa. Since this is a study on a small opening of the whole screen module, the side B.C.s are symmetry. <\/p>\n

I surfed the internet and have tried the following suggested solutions but neither has worked so far:<\/p>\n

1- I extended the domain length and put the outlet 100mm away from the last screen layer. (as a comparison, the distance between the layers is 3 mm in my geometry). I am pretty sure that this length is enough because the pressure does not change from the last layer until very close to the outlet.<\/p>\n

2- I increased the grid resolution. my cells are poly-hexcore and the initial cell sizes were 1.6e-5m and 3.2e-5m. I studied the case with a mesh of half of this size and the backflow is still here. It is noteworthy that the cell sizes are smaller close to the wires.<\/p>\n

3- I decreased the “Pseudo time explicit relaxation factors” through solution>controls down to 0.1 and it didn’t solve the problem.<\/p>\n

4- I won’t get any backflows if I change my outlet BC from pressure outlet to outflow. However, this BC should not be selected for compressible gases based on the manual, so I don’t think this is an appropriate solution for my case.<\/p>\n

Attached you can see screenshots of pathlines colored by static pressure in the range of -0.01 to 0.01 Pa. Very close to the outlet, the flow is deflected downward and there’s a backflow on the top part of the outlet. There is also a vertical pressure gradient which makes no sense. I expect a constant 0 Pa pressure from a little away from the last screen layer all the way to the outlet. <\/p>\n

Can you please help me how I can solve this issue?<\/p>\n

Thanks in advance<\/p>\n

<\/p>\n

Path line colored by static pressure for vel= 0.005 m\/s – 45% back flow<\/span><\/p>\n

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