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How set experimental points values as wind tunnel boundary conditions |
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December 22, 2012, 13:47 |
How set experimental points values as wind tunnel boundary conditions
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#1 |
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Davide Tartarini
Join Date: Dec 2012
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Hi everyone, my first thread..
I had to test car performances using a k-epsilon realizable model in a slotted walls WT and I need to impose some experimental point values (pressure) as wind tunnel wall boundary conditions. How can I impose a wall pressure conditions like this? Is it possible? thank you all, if you need some extra info please ask! |
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December 23, 2012, 01:05 |
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#2 |
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Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
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Without doing some magic, you cannot specify the pressure on the wall.
You must follow the physical mathematics of what each boundary condition is. For a solid wall, this means that the wall-normal velocity is equal to the wall velocity (kinematics). For the no-slip condition, the tangential velocity is equal to the wall tangential velocity. If there is a slip-condition then tangential velocity is related to the wall tangential velocity by some relation. Note, there is no pressure! Think of it this way. You cannot specify the pressure at the wall in your wind tunnel either. You can try by various methods to adjust the tunnel conditions to obtain a certain pressure at the wall but by no means are you specifying the pressure at the wall, you are just changing the inlet and outlet conditions of your wind tunnel. With that said, I have seen cases where variables are "fixed" over an entire zone. Not sure if you can do specific locations (possibly with a UDF). If you set the pressure in this manner, you will end up with inconsistencies and your solution most likely will have trouble converging / converging to an inaccurate result. Last edited by LuckyTran; December 23, 2012 at 01:30. |
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December 23, 2012, 10:56 |
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#3 | |
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Davide Tartarini
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December 23, 2012, 16:02 |
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#4 |
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Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
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I recommend visiting the Fluent Manual section 7.2.4 on Fixing the Values of Variables. I have used it before for fixing y,z velocity in an entire zone. You can specify pressure if you are using the pressure-based solver. Like all the default properties in Fluent, it is designed for you to fix variables throughout an entire zone and not a single point.
You can specify non-constant profiles by specifying the profile or using a UDF. If you construct the correct profile/UDF then I imagine you can get it to specify the pressure at a specific location. Sorry I can't give a complete walkthrough after that as I avoid these options (complicated CFD is not very useful, IMO). But it is possible and fairly straightforward (if you can get the profile/UDF). You do not need to change the solver, wall functions, or mess with the details of the turbulence modeling. |
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experimental data, k-epsilon model, pressure boundaries, wind tunnel |
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