There are two ways to incooperate such a loss. 1) You model the perforated plate as as a very thin porosity. For this you would need a thin volume mesh in that region and apply the loss via a general momentum source or via the porosity settings. 2) You model the pressure jump with an interface. For this you need an interface (can be 1:1) at the location of the perforated plate. Then go to interface settings -> Additional Interface model -> Interface model -> Pressure change Here can define an expression of the form: dp = a *v + b * v * |v| This can be used in the interface settings. Attached please find a test case demonstrating the second approach.