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Initial values and boundary condition for LES simulation of a box |
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July 30, 2018, 13:20 |
Initial values and boundary condition for LES simulation of a box
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#1 |
New Member
Saddam Hijazi
Join Date: May 2016
Posts: 17
Rep Power: 10 |
Hello everybody,
I am trying to simulate a case using LES turbulent approach, my case is in 3D where I have a box placed inside a rectangular parallelepiped on its bottom surface. Each side of the box is 0.1 meter length and the parallelepiped is 2 X 1 X 0.5 meter. I am using dynamicKEqn as LES model and I want to simulate the case with initial velocity field being (1 0 0) at the inlet, the box is placed 0.2 meter far from the inlet leaving 1.8 meter for the wake region. I checked online for the boundary conditions that I should use and I found that I should use fixedvalue for inlet and inletoutlet for the outlet, but I have doubt about the values and the type of conditions I should use for nut and k. Here are the nut and k in the zero folder FoamFile { version 2.0; format ascii; class volScalarField; object k; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -2 0 0 0 0]; internalField uniform 0.000384; boundaryField { inlet { type fixedValue; value $internalField; } outlet { type inletOutlet; inletValue $internalField; value $internalField; } sides { type fixedValue; value uniform 0; } top { type zeroGradient; } bottom { type zeroGradient; } box { type fixedValue; value uniform 0; } } // ************************************************** *********************** // FoamFile { version 2.0; format ascii; class volScalarField; location "0"; object nut; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 2 -1 0 0 0 0]; internalField uniform 0.001; boundaryField { inlet { type fixedValue; value $internalField; } outlet { type inletOutlet; inletValue $internalField; value $internalField; } sides { type fixedValue; value uniform 0; } top { type zeroGradient; } bottom { type zeroGradient; } box { type nutkWallFunction; value uniform 0; } } // ************************************************** *********************** // The physical viscosity is 10-5 and so Re = 10^4 I am particularly confused about the values of nut and k, I computed the value of k using the indications mentioned in this page https://www.cfd-online.com/Wiki/Turb...ary_conditions where I supposed that Re_dh is just the same as Re (meaning that I supposed dh to be d the length of any side of the box) second thing what about the use of the wall function for nut is it ok to have zero value on the box ? Note that my mesh is coarse but once I verify the correctness of the boundary and initial setting I will run the same case on 8 times more cells mesh but on the cluster as my laptop does not afford running it. Thank you very much for your help. |
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July 31, 2018, 03:21 |
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#2 | |
Senior Member
Santiago Lopez Castano
Join Date: Nov 2012
Posts: 354
Rep Power: 15 |
Quote:
Setting k for the inlet depends entirely on how you produce your boundary data. For instance, if you map your inlet from DNS data then k is zero at the inlet. Instead, if the data you map comes from LES then you should be able also to map the k sgs to the inlet as well. Advise: much of you know for turbulence in RANS is useless for LES, except if you are using hybrid methods. |
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boundary condition, initial condition, les, turbulence, turbulent |
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