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Sometimes it is useful to know the flow across a plane in certain direction instead of the net flow. In CFX-Post create an expression for the velocity in the desired direction: 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,parallel to the direction of flow. 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 locator (which is generally normal to the flow vector). This works for boundaries and CFX-Post locators, e.g: flow = areaInt(VelFace)@opening flow = areaInt(VelFace)@Plane 1