pressure distribution for an orifice flow 1

[ybzh]

Hi, all,

I am modeling an orifice flow (flow through a small hole in a microchannel) using CFD software. I have simulated the pressure distribution near the orifice and the pressure distribution on the plate.

Now I want to compare the simulation result to the theoretical result. Can someone can advice a textbook or some weblink? Thank much.

 

[sailoday28]

What is the fluid, upstream, downstream conditions (Temperature, pressure), and mass flow?

 

[ybzh]

Basically I want to model a valve using the orifice flow model. Water is used as the fluid. The temperature can be taken as room temperature. The downstream pressure is zero. The upstream pressure is from 0 to 100 kPa.

The microchannel has a cross section about 300 by 300 micron. There are a compliant flap and a rigid stopper sitting closely each other within the microchannel. Under reverse pressure, the flap moves towards the stopper forming an orifice. We found that the leakage saturates for reverse pressure range of 40-100 kPa, and we want to simulate this behavior.

I first calculated the pressure distribution using 2D FEM. Then we want to compare this simulation result with theoretical result. This is to see whether the fluid-solid is strongly or weakly coupled. I really hope to find an textbook or some paper which has the pressure distribution for the orifice flow. Thanks.

 

[MikeHalloran]

Given a circular orifice of diameter d in a bulkhead of thickness d-ish, separating two chambers of dimensions >>d, said chambers filled with liquid, and a pressure difference causing flow through the orifice, ...

The upstream isobars are hemispheric, i.e., the flow in the vicinity of the orifice is everywhere radial toward the orifice.

The downstream isobars are of more complex geometry. The flow exiting the orifice induces toroidal circulation within the surrounding liquid, so the flow along the face of the bulkhead on the downstream side is radially inward toward the orifice. The jet of fluid leaving the orifice grows in diameter and slows down as it diffuses into the surrounding fluid, slowly. There is no 'vena contracta' as with a liquid jet entering a gas.

I don't know of a paper or book that deals adequately with the subject. The above is inferred from years of observations of Coulter Counter(r) apertures from 50um to 4000um diameter, with bulk orifice velocities up to 10m/s.

I'm a little fuzzy on your actual geometry, but I suspect the saturation you describe has to do with an interaction between the square law relationship of pressure drop and flow across an orifice and the compliance of your flap.



Mike Halloran
Pembroke Pines, FL, USA

 

[ybzh]

Thank you so much, MikeHalloran. These are very useful informations! You are really an expert. I also looked into a book "Handbook of Hydraulic Resistance", which is a very good book, but I did not get the information on pressure profile. Seems I have do just use simulate pressure distribution using software.

 

[cbrn]

Hi,
I have a textbook where you could find some theoretical / analytical information that you may use for your problem (it is not described "as is", but I think there are some configurations described there that you may extrapolate). Unfortunately, it is in Italian:
"Idraulica", by Augusto Ghetti, edition Librerie Cortina - Padova, ISBN 88-7784-052-8.
Unfortunately, it seems that there is no simple way to get the isobar config downstream, or you have to apply manually something like the Finite Differences. But then, why not rely on CFD + labo experiments?

Regards