# Numerical Simulation of Free Surface over Spillway

In this post, i presented my simulation of free surface over cylindrical spillway using OpenFOAM solver (interFoam).
following steps are conducted for preparing case:

## Create grid with OpenFOAM mesh generators

• generate base grid with blockMesh
• extract spillway from base grid and refine locally around spillway with snappyHexMesh
• extrude front patch to create 2D grid for simulation

The extrudeMeshDict setup is:

```constructFrom patch;
sourceCase ".";
sourcePatches (front);

exposedPatchName back;

flipNormals false;

extrudeModel linearNormal;

nLayers 1;

expansionRatio 1.0;

linearNormalCoeffs
{
thickness 0.1;
}
mergeFaces false;
mergeTol 0;```

snappyHexMesh divides cells in z direction which is not suitable for 2D simulation. Thus extrudeMesh extrudes the front patch, so the final grid have only one cell in z direction. The final grid is shown below:

## Simulation settings and result

• apply setFields to create non-uniform initial condition for volume fraction
•  apply blank roughness using wall function nutRoughWallFunction via turbulence model
•  run solver interFoam
• add appropriate functions  into controlDict via swak4Foam for post processing. For example, the depth of water over spillway crest is calculated as follow:
```depthOverCrest
{
type     swakExpression;
valueType    set;
verbose    true;
setName    yb1;
set
{
type    uniform;
axis    y;
start   ( 0 -0.175 -0.15 );
end     ( 0  0.175 -0.15 );
nPoints   60;
}
aliases  { alpha1  alpha.water; }
expression "(alpha1 > 0.5) ? pos().y+0.175 :0";
accumulations (max);
interpolate   true;
interpolationType   cellPoint ;
outputControlMode   timeStep;
outputInterval   1;
}```

For inlet, variableHeightFlowRate  and variableHeightFlowRateInletVelocity is employed for alpha.water and velocity, respectively. These BCs consider the effect of down stream on the patch.

## 2 Replies to “Numerical Simulation of Free Surface over Spillway”

1. JFM says:

Hi Nima – I am curious to which BCs you used for this model.

Regards
JFM

1. Nima Samkhaniani says:

i will edit the post and add the bc condition information