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Swirl-Velocity Specification of 2-D Fan Boundary Condition |
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#1 |
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I opened a relevant thread before at the student community forums of ANSYS but did not find a closure about the subject (i.e. https://studentcommunity.ansys.com/t...ary-condition/ ). I'll appreciate any help from the cfd-online community.
I am defined a 2-D fan model using the fan boundary condition on a square surface in a 3-D simulation of a room. I am puzzled by how Fluent interprets the tangential velocity since the tangential velocity I get as a result is always less than what I input, and typically half of the constant value I input as tangential velocity (i.e. when I use values on the order of axial velocity). The results below correspond to the case with a constant tangential velocity of 1 m/s. According to the plot of tangential velocity as a function of y direction along the midline of the fan surface, the values plateaued at around 0.5 m/s outside hub (half of the input). How should I interpret this? ![]() ![]() I'll greatly appreciate your help in clarifying how Fluent uses inputs for tangential velocity in the 2-D fan boundary condition? Why don't I see the tangential velocity imposed between the hub radius and outer dimension of the boundary surface as I define? Is there a physical reasoning behind this? |
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#2 |
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Lucky
Join Date: Apr 2011
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Which boundary condition are you using? Fluent doesn't have a "fan boundary condition" Just post a screenshot of your boundary condition input.
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#3 |
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Here is the screenshot of what I use.
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#4 |
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Any help from the community would be appreciated.
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#5 |
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yanki cob
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Can you check velocities slightly downstream/upstream of the fan surface?
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#6 | |
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Quote:
2. X velocity 3. Z velocity at the velocity inlet and fan bc |
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#7 |
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yanki cob
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OK, but can you change the contour plane to another plane that is slightly downstream/upstream of the fan plane? Like, 5mm away from the fan.
Also, why do you have a velocity inlet BC? Last edited by yanki; October 3, 2018 at 08:51. Reason: added |
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#8 | |
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Quote:
Attached are contours for 5mm upstream, fan and 5mm downstream with the same scale. Thanks |
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#9 |
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yanki cob
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So, the max. velocity 5mm downstream is higher than max. velocity on fan plane, right?
Can you find a plane with the velocity value that you input (1m/s I guess)? Try to turn OFF the node values. |
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#10 | |
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Quote:
I have attached the contour at 25 mm downstream of the fan, where the tangential velocity becomes 1 m/s (node values off). I guess I understand where you are going. Does the fan BC impose the tangential velocity within the first cell downstream of the fan, since the cell size is 25 mm? |
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#11 | |
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yanki cob
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I don't know how the BC works, and couldn't find any explanation on the theory/user guide. But there might be an averaging problem, that's why I asked for turned off nodes.
As I understand, this is not a "problem" for you, you just wanted to make sure that the fan BC works the way it intended to. Quote:
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Tags |
3-d simulation, fan boundary condition, swirl, tangential velocity |
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