Hi all,

I'm modeling a water flow in circular duct through a concentric orfice plate. The boundary condition I use is wall, axis, velocity inlet and outflow.

I intend to model the flow in various reynolds number from laminar to turbulent and different A0/A1 ratios.

I'm not familiar with the periodic boundary condition, can I apply them in this specific case ??

And one more thing...Does anyone know an empirical equation to estimate the separation bubble length formed after orifice plate or the length to fully developed flow profile (not Le/D=0.06*Re for laminar or Le/D=4.4*Re^(1/6) for turbulent).

Thanks in advance John

You can not use the periodic boundary condition as this would be representative of many orifice plates. If you have fully developed flow before your orifice plate you should either have a sufficiently long upstream section to allow the flow to numerically develop, or use a periodic boundary condition on a straight pipe flow problem to generate a fully developed profile.

Why do you need the bubble length? If it is for estimating the required downstream length for your outlet boundary condition then a distance of 10 to 20 pipe diameters should be ok. I do not know of an equation for estimating recirculation (i.e. 'bubble') length.