Pressure drop over orifice in pipe

Appa

Hey all,

I'd need help with determining the pressure loss over an orifice in a pipe. I have an equation for the friction factor so no problem there, and I know the Reynold's number as well. What confuses me is choosing the suitable velocity for the pressure drop equation;

[itex]\frac{Δp}{ΔL}[/itex] = ζρ[itex]\frac{{v^{2}}}{2D_{h}}[/itex]

The thickness of the orifice varies so the initial velocity corresponding to the Reynold's number surely won't be the most accurate choise for the pressure drop calculation, will it? (The thickness over hydraulic diameter will vary between 0 and 10).

This is not a homework question! I want to approximate the pressure drop in order to validate a CFD model of the orifice.

Cheers,
A