XANSYS Message: 20634 [Go back to message list]
[bookmark on del.icio.us]
No rating yet
Subject: Re: [FLOT] orifice
Author: Mark Troscinski
Date: 2001-01-30 13:35:00Hi Mark,
Sure. For a straight tube where the upstream (1) and downstream (2) areas
and velocities are constant, the discharge coefficient, Cd, is the
difference in static pressure measured across the orifice, normalized by the
flows dynamic head, or:
Cd = (P2-P1)/(0.5*rho*V**2)
When calculating Cd from a computed CFD solution, the key is knowing where
to "measure" the upstream and downstream static pressures. Most references
site D:1/2D taps, i.e., pipe-wall taps at D upstream and 1/2D downstream of
the orifice plate. I normally check nodal values of PRES nearest to these
wall locations, but from my experience, especially with laminar flows,
moving one or two nodes over can dramatically affect this "measured"
pressure difference.
Keep in mind that although the geometry for orifice flows is quite simple,
the flow physics is very complex. A strong shear layer is formed as the
fluid squeezes through the orifice, and ample mesh refinement in the orifice
region is needed to properly capture the physics.
Hope this helps.
Mark Troscinski
> -----Original Message-----
> From: WISHAH7@n... [SMTP:WISHAH7@n...]
> Sent: Friday, January 26, 2001 9:41 AM
> To: xansys
> Subject: [xansys] orifice
> hi everyone
> i would like to ask a question regarding the orifice flow, is there is any
> way of calculating the discharge coefficient for laminar flow through
> orifices using ansys flotran.
> thanks all
> mark