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atmBoundaryLayerInletVelocity

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Old   May 25, 2016, 12:08
Default atmBoundaryLayerInletVelocity
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Almond Wong
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Hi, can some explain the terms use for this file?

While looking into the turbineSiting tutorial:
the inlet is:
inlet
{
type atmBoundaryLayerInletVelocity;
#include "include/ABLConditions"
}

and the subsequent ABLConditions file has this:
Uref 10.0;
Zref 20;
zDir (0 0 1);
flowDir (1 0 0);
z0 uniform 0.1;
zGround uniform 935.0;
value $internalField;

I would like to know what does the terms in the ABLConditions file represent.

Many thanks in advance
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Old   May 25, 2016, 12:32
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If someone could provide some example, it will be awesome!!!

Last edited by BakedAlmonds; May 25, 2016 at 16:14.
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Old   May 26, 2016, 11:35
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Paulo Vatavuk
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Hi BakedAlmonds,

In the C++ documentation you may look at the code for atmBoundaryLayer.H, there you will find the description of the variables.
This boundary condition uses the logaritmic profile for the wind inlet velocity:

U = (Ustar/kappa) ln( (z - zGround + z0)/z0 )

where:
kappa is the von Karman constant (=0.41)
z is the vertical coordinate
zGround is the z position of the ground
z0 is the terrain rugosity

Ustar can be calculated imposing that at height Zref you have velocity Uref this results in

Ustar=Uref*kappa/( ln( (Zref+z_0)/z_0 )

Concluding
Uref is the velocity a height Zref
Zref is the height (z-zGround) where the velocity is Uref
zDir is the vector that indicates the vertical direction
flowDir is the vector that indicates the wind direction
z0 is the terrain rugosity
zGround is the z coordinate of the ground

I hope this helps.

Paulo
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Old   May 31, 2016, 08:29
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Almond Wong
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Hi Paulo, thanks for the reply. I had an attempt to try out the atm function with the following as my boundary conditions:

ABLConditions:
Uref 10.0;
Zref 500;
zDir (0 0 1);
flowDir (1 0 0);
z0 uniform 0.1;
zGround uniform 0.0;
value $internalField;

I set my top and sides patches to symmetry.

Then I realise two weird occurrences. Hope someone could assist me on this.

1) I tried to verify the inlet velocity profile so I added probes to check.

My inlet patch are bounded by vertices :
( -1100 , -1100 , 0)
( -1100 , 1100 , 0)
( -1100 , 1100 ,1100)
( -1100 , -1100 , 1100)

then i place my probes as
( -1100 0 10 )
.
.
.
.
( -1100 0 500 )

I realise that the velocity at Zref the very first time step is less than the Uref. Shouldn't it be very close if not more than that specified?

2) The velocity at the walls act like a viscous BL. Shouldn't it act as if its frictionless?
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Old   March 15, 2017, 08:21
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Nathan
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Hello,
I am a French student, and I try to integrate a logarithmic wind profile in a simulation highlighting the eccentricity around a building. Could you help me by explaining how to use the atmboundarylayerinletvelocity function? How can we integrate it in place of the uniform wind field that we currently have? Would you have any examples on which we could rely?

Thanks in advance
Nathan
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