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Louvered vent blows at the wrong angle #13213
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This is typical of OPEN boundaries. The flow is exiting the vent at the correct angle. But OPEN bcs like flow to be normal to the boundary. They are not good at maintaining flows that are at an angle. If you know this angle on the boundary, then you need to set it with with parameters on the WIND line. But I assume this is a subdomain of a real case, there you can move your boundaries far enough away that they do not affect the local vent, or if there are walls this would be a more well defined boundary for the flow problem. |
Look at the flow vectors in the vicinity of your vent. Add |
Resolution also matters. 10 x 10 x 5 m domain with a 1 m wide wall segment 2 m from the -x and +y boudaries. The wall has a 1 m wide vent that is 0.6 m high at the mid-height of the domain. Images show the results for 2.5, 5, and 10 cm. As resolution improves, the angle improves. 10 cm case shown below. &HEAD CHID='45-10'/ &TIME T_END=20/ &MESH XB=0,5,0,5,0,5,IJK=50,50,50,MULT_ID='M'/ &RADI RADIATION=F/ &VENT PBX=0,SURF_ID='OPEN'/ &SURF ID='LOUVER',VEL=-2,VEL_T=-2,0,COLOR='BLUE'/ &OBST XB=2.0,2.1,7.0,8.0,0.0,5.0/ &SLCF QUANTITY='VELOCITY',VECTOR=T,PBZ=2.5/ |
Hello, thanks for your reply and taking the time to test things out on your side. I didn't expect the mesh to need such a fine resolution! Sadly, it does not bode well for my real case (over 150 thin vents in quite a big domain) and the cell count. For now, I will reduce VEL_T to approximatively match the 45° for a given flowrate and that will have to do! Thanks everybody for the guidance, much appreciated (and I shall be more exhaustive with convergence studies in the future)! |
Our of curiosity, have you mapped out the velocity profile in the vicinity of an actual louvered vent? |
If you mean with respect to a real physical vent, I have not. I must add that I need louvered vents not because they are actually louvered vents, but because the vents themselves are located at regular intervals over a circle and blowing at different angles than the cartesian directions. I was hoping I could cheat my way with this feature! HVAC vents can also be louvered, maybe they are less sensitive to the cellsize? |
I was definitively confused by the interaction between poor resolution and induced flow motion, thanks for the clear explanation abount the edges! |
When using a louvered vent, the actual airflow does not match the expected angle. The validation case does work, but when using a smaller vent, the angle tends to be larger than the input with respect to the vent normal.
Here is the FDS case (Pyrosim and FDS 6.9 on Windows 10):
`
&HEAD CHID='case2'/
&TIME T_END=20.0/
&DUMP DT_RESTART=300.0, DT_SL3D=0.25/
&MESH ID='MESH', IJK=69,64,22, XB=0.0,6.9,-2.4,4.0,0.6,2.8/
&SURF ID='louvered_vent',
COLOR='RED',
HEAT_TRANSFER_COEFFICIENT=0.0,
VEL=-3.0,
TAU_V=-1.0,
VEL_T=-3.0,0.0/
&OBST ID='Obstruction', XB=0.0,0.2,2.0,4.0,0.05,2.8/
&VENT ID='Mesh Vent: MESH [XMAX]', SURF_ID='OPEN', XB=6.9,6.9,-2.4,4.0,0.6,2.8/
&VENT ID='Mesh Vent: MESH [XMIN]', SURF_ID='OPEN', XB=0.0,0.0,-2.4,4.0,0.6,2.8/
&VENT ID='Mesh Vent: MESH [YMAX]', SURF_ID='OPEN', XB=0.0,6.9,4.0,4.0,0.6,2.8/
&VENT ID='Mesh Vent: MESH [YMIN]', SURF_ID='OPEN', XB=0.0,6.9,-2.4,-2.4,0.6,2.8/
&VENT ID='Vent02', SURF_ID='louvered_vent', XB=0.2,0.2,2.0,4.0,1.681824,2.290319/
&SLCF QUANTITY='VELOCITY', ID='velocity', XB=0.0,6.9,-2.4,4.0,0.0,3.0/
&SLCF QUANTITY='U-VELOCITY', ID='velocityX', XB=0.0,6.9,-2.4,4.0,0.0,3.0/
&SLCF QUANTITY='V-VELOCITY', ID='velocityY', XB=0.0,6.9,-2.4,4.0,0.0,3.0/
&TAIL /
`
The inflow should follow a 45° line from the vent.
Here is the velocity field when using a small vent:
![image](https://private-user-images.githubusercontent.com/176484512/351683372-9e6909b1-abd9-4b4d-8835-f7fd592fa462.png?jwt=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJnaXRodWIuY29tIiwiYXVkIjoicmF3LmdpdGh1YnVzZXJjb250ZW50LmNvbSIsImtleSI6ImtleTUiLCJleHAiOjE3MjU3NzY3OTUsIm5iZiI6MTcyNTc3NjQ5NSwicGF0aCI6Ii8xNzY0ODQ1MTIvMzUxNjgzMzcyLTllNjkwOWIxLWFiZDktNGI0ZC04ODM1LWY3ZmQ1OTJmYTQ2Mi5wbmc_WC1BbXotQWxnb3JpdGhtPUFXUzQtSE1BQy1TSEEyNTYmWC1BbXotQ3JlZGVudGlhbD1BS0lBVkNPRFlMU0E1M1BRSzRaQSUyRjIwMjQwOTA4JTJGdXMtZWFzdC0xJTJGczMlMkZhd3M0X3JlcXVlc3QmWC1BbXotRGF0ZT0yMDI0MDkwOFQwNjIxMzVaJlgtQW16LUV4cGlyZXM9MzAwJlgtQW16LVNpZ25hdHVyZT0wYzU3ODAyNDcyMmUwNjlhMWY4NzQ4NzU4YzE2OWY2NGFmZGYzYzMzMDU4MmU2ZWUzYmY3MGI1MjMxZTQ0ZWNiJlgtQW16LVNpZ25lZEhlYWRlcnM9aG9zdCZhY3Rvcl9pZD0wJmtleV9pZD0wJnJlcG9faWQ9MCJ9.Fe6nReBmx-xDotrXSxsfg2k9h3GP86SedXU-ILN_9WY)
Here is the velocity when the whole XMIN boundary is set to use the louvered vent SURF:
![image](https://private-user-images.githubusercontent.com/176484512/351706182-92541593-eb82-4e67-b4c3-448acb604546.png?jwt=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJnaXRodWIuY29tIiwiYXVkIjoicmF3LmdpdGh1YnVzZXJjb250ZW50LmNvbSIsImtleSI6ImtleTUiLCJleHAiOjE3MjU3NzY3OTUsIm5iZiI6MTcyNTc3NjQ5NSwicGF0aCI6Ii8xNzY0ODQ1MTIvMzUxNzA2MTgyLTkyNTQxNTkzLWViODItNGU2Ny1iNGMzLTQ0OGFjYjYwNDU0Ni5wbmc_WC1BbXotQWxnb3JpdGhtPUFXUzQtSE1BQy1TSEEyNTYmWC1BbXotQ3JlZGVudGlhbD1BS0lBVkNPRFlMU0E1M1BRSzRaQSUyRjIwMjQwOTA4JTJGdXMtZWFzdC0xJTJGczMlMkZhd3M0X3JlcXVlc3QmWC1BbXotRGF0ZT0yMDI0MDkwOFQwNjIxMzVaJlgtQW16LUV4cGlyZXM9MzAwJlgtQW16LVNpZ25hdHVyZT1lNzljNmZiOTI4ODYxM2QyMWQ2NDE0MGEyMmMzYjg4NjE5MTBlNmE0YjA4YWI0ZmVlMWUyNjNiZjg3MDI4N2ExJlgtQW16LVNpZ25lZEhlYWRlcnM9aG9zdCZhY3Rvcl9pZD0wJmtleV9pZD0wJnJlcG9faWQ9MCJ9.RxXOTqpAhXYiom0_89uaS7K6kVZeCjwUJ9cdbtg72Pc)
I cannot explain why there is such a difference between the two cases. I believe the mesh is fine enough to resolve the vent properly.
Thanks for the help!
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