I’m attempting to use the semi-permeable membrane with no results. I’ve simplified the program to a cylinder with mass inflow and pressure outflow. Between the two is a 50 cm tube with a 5 cm length box region with y-axis semipermeable membrane in the middle. Fluid permeability and the internal resistance coefficient is set to 1.84e-9 m^2 and 88800 1/m, respectively. Over a 5 cm length that should result in a 950 Pa pressure drop. However, I only see the same 6 Pa loss with or without the region. Is there an example that utilizes the semi permeable membrane or something people typically miss?
Hi @bobbyamerica1
You are correct that none of the provided tutorials use a semipermeable internal surface.
Please upload your project files so we can have a look - Main menu → Submit bug report, then upload the ZIP file here
Thank you for taking a look. The membrane works as expected when the walls are bounded by the edge of the domain as seen in the attached *with_box variation. However, once a cylinder is introduced the membrane has no effect. The rest of the simulation seems to make sense in either case.
fluid_bed_tfm_3d_with_box_2024-06-21T002155.838205.zip (2.8 MB)
fluid_bed_tfm_3d_with_cylinder_2024-06-21T002908.534156.zip (19.1 MB)
Hi again,
I have simplified the case further. It appears when an stl is present anywhere in the scene the internal surface has no effect. The presence of an stl changes cartesian grid to true. I’m still trying to figure out the ramifications of that.
I have attached two cases below. Each has the flow bounded by the edges of the mesh with mass inflow and pressure outflow and an internal surface set as a Y-axis semi-permeable membrane. With no additional geometry the internal surface functions as expected. Without it, it has no effect.
Does anyone know if this is a bug or intended behavior?
Working IS -
withoutstlsphere.zip (348.7 KB)
Broken IS -
withstlsphere.zip (3.0 MB)