Q)
How do I calculate the gross flow across a plane?
A)
Sometimes it is useful to know the flow across a plane in one direction only instead of the net flow.
For example it may be useful to know how much total flow is coming in across an opening.
In CFXPost create an expression for the velocity normal to a face, e.g:
LIBRARY:
CEL:
EXPRESSIONS:
VelFaceExp=max(u*nx+ v*ny+w*nz, 0.0 [m/s])
END
END
END
where (nx,ny,nz) are the x,y,z components of the unit normal vector, that is normal to the required face.
The max function ensures that only flows in the direction of the normal give a positive result.
Then create a scalar variable using this expression:
USER SCALAR VARIABLE:VelFace
Boundary Values = Conservative
Calculate Global Range = Off
Expression = VelFaceExp
Recipe = Expression
Variable to Copy = Pressure
END
The gross flow across a plane is then given by the area integral of the variable over the required locator.
This works for bondaries and CFXPost locators, e.g:
flow = areaInt(VelFace)@opening
flow = areaInt(VelFace)@Plane 1
Q) How do I calculate the gross flow across a plane? A) Sometimes it is useful to know the flow across a plane in one direction only instead of the net flow. For example it may be useful to know how much total flow is coming in across an opening. In CFXPost create an expression for the velocity normal to a face, e.g: LIBRARY: CEL: EXPRESSIONS: VelFaceExp=max(u*nx+ v*ny+w*nz, 0.0 [m/s]) END END END where (nx,ny,nz) are the x,y,z components of the unit normal vector, that is normal to the required face. The max function ensures that only flows in the direction of the normal give a positive result. Then create a scalar variable using this expression: USER SCALAR VARIABLE:VelFace Boundary Values = Conservative Calculate Global Range = Off Expression = VelFaceExp Recipe = Expression Variable to Copy = Pressure END The gross flow across a plane is then given by the area integral of the variable over the required locator. This works for bondaries and CFXPost locators, e.g: flow = areaInt(VelFace)@opening flow = areaInt(VelFace)@Plane 1 

