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Spillway simulation with interfoam, water disappearing through atmosphere

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Old   January 21, 2014, 03:52
Default Spillway simulation with interfoam, water disappearing through atmosphere
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Christian Wokl
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Dear Foamers,

I am trying to simulate a spillway which is about 300meters long but just 2.5 meters wide. I ran into several problems now. just when i thought i solved them another appeared and i'm totally lost on this one. I need to simulate it in 3d since the spillway is curved and the angle of the slopes vary. Both models consist of a inlet (bottom of reservoir) walls and atmosphere (including outlet)

I searched this forum a lot for correct boundaries and fvschemes according to my checkmesh output. There are 2 pictures attached of a short version and a little longer version of the spillway. CheckMesh was Ok for both Meshes (non-ortho max69, average 19; max skewness 0.86) this values dont differ significant for both meshes. I guess they are ok since the result of one simualtion at least looks somehow ok...

Boundaries: P-rgh: inlet: buoyantPressure 0
wall: buoynatPressure 0
atmosphere: totalPressure

U: inlet:flowRateInletVelocity 10
wall: fixed 0 0 0
atmosphere: pressureInletOutletVelocity 0 0 0

alpha: inlet: fixedValue 1
wall: zeroGradient
atmosphere: inletoutlet 0 0

i also tried zeroGradient boundaries and specifying an extra outlet but the error that occured was that the step decreased to a minimum when the liquid phase came close to the outlet.

the schemes i used: ddt: euler

grad: default Gauss linear;
grad(U) cellLimitedFaussLinear 1;

div: div(rho*phi,U) Gauss linearUpwindV grad(U);
div(phi,alpha) Gauss vanLeer;
div(phirb, alpha) Gauss interFaceCompression;


So Problem now is: I just extended my slope and the water flows out through the atmosphere isntead of down the slope. Gravity checked

Another question is: i expected the water flow to have highest velovity in the center of the slope. apparently fastest lanes are close to the edges of the slope. Might that be due to mesh, since the cells are finer meshed in the edges (~100degrees not just rectangle).

Mehing was done with salome (Tetra,triangle,wire). Mesh sizes are 90000 for small model and 130000 for larger one

If anyone has an idea i'd be more than thankful
christian

edit: turbulenceModel kOmegaSST
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File Type: jpg comparisonslopes.jpg (73.3 KB, 109 views)
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Old   January 21, 2014, 22:42
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Hi,

How about your pressure BCs? Try the following BCs for pressure:

atmosphere_body
{
type totalPressure;
p0 uniform 0;
U U;
phi phi;
rho rho;
psi none;
gamma 1;
value uniform 0;

}

Inlet_body (and others)
{
type fixedFluxPressure;
value uniform 0;

}
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Old   January 22, 2014, 03:41
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Christian Wokl
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Thx,

in about 1 hour ore a little more i'll let u know if it worked.

christian
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Old   January 22, 2014, 05:56
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Christian Wokl
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hey,

very strange behaviour: it somehow matters wheter my reservoir is located at z= 15meters or z=100 meters.
I made a new model with higher walls at the reservoir and located the reservoir at lower values for z.
water is now again streaming down the channel. but it doesnt look correct at all. basically i know that in reality this spillway is filled about half way with water by spilling the simulated amount of water down the way. i just get some areas sort of wet (sorry for bad english)

Is maybe the friction too low and the water speeds up too fast so that there's no chance for it to build a closed surface?
and again the highest alpha values are located next to the walls and not in the center of the way. In the beginning of the slope the water stops flowing down in the center of the way. Does someone have an explanation for it?

The transport properties are equal to those used in the interfoam tutorial dambreak.

Changing my boundaries for p_rgh didnt make a change (bouyantpressure or fixedFlux)

thx Christian
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File Type: jpg Bildschirmfoto vom 2014-01-22 10_38_32.jpg (44.4 KB, 69 views)
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Old   January 23, 2014, 04:02
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Christian Wokl
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Hey all,

I'm posting an actual picture which shows my problem. Is this an meshing problem (too large cell sizes clos to walls?). the velocity of water on the surface in the end of the slope is about 20m/s. isn't that a little too fast?

Thx
Christian
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File Type: jpg strangeflow.jpg (43.6 KB, 69 views)
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Old   July 12, 2016, 10:42
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Hello Wokl,

Did you find the problem?
I guess it could be about the tetrahedral mesh or the p_rgh field initialization.

Cheers,
Lourenšo
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