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-   -   pressure outlet of orifices (https://www.cfd-online.com/Forums/fluent/148008-pressure-outlet-orifices.html)

amin.z February 3, 2015 07:43
pressure outlet of orifices
 
hey friends

I should compare two different orifices in fluent but I have an issue!
I have physical properties of the liquid, geometrical properties of orifices and static pressure at inlet
But I need to calculate the pressure of outlet for each of them
I'm confused to selecting an appropriate outlet boundary for calculating pressure at outlet!:confused::confused:
any ideas friends?

ghost82 February 5, 2015 05:06
Hi Amin, I would draw a long pipe next to the plate, so to have a completely developed fluid; and then I would set outflow bc to let fluent calculate the pressure drop.

Daniele

amin.z February 5, 2015 05:16
Quote:
Originally Posted by ghost82 (Post 530503)
Hi Amin, I would draw a long pipe next to the plate, so to have a completely developed fluid; and then I would set outflow bc to let fluent calculate the pressure drop.

Daniele
Hey dear friend
I'm used this method, I used a long channel after the orifice, my inlet BC is pre. inlet and outlet BC is pre. outlet.
But the pressure distribution is strongly dependent to outlet gauge pressure while I haven't any information from outlet!

ghost82 February 5, 2015 05:20
No amin,
I suggested to set the inlet as velocity or mass flow inlet and the outlet as outflow (because you have no info about pressure/velocity distribution, and pressure inlet is not compatible with outflow).
You need completely developed flow to apply the outflow bc.

However, take care to your problem, and take care where these orifices are installed: I did some simulation about cavitation in orifices.
The plates were installed next to a pump, in a closed loop; Tank-->pump-->orifice-->tank and so on.
Pressure outlet was always atmospheric, independently of the pressure inlet given by the pump, because the tank was open to atmosphere.

amin.z February 5, 2015 05:29
But mass flow inlet is one of the unknown values of the problem
But maybe velocity inlet could help me!
Good idea dear friend! Tnx!

And another question! is this method suitable for ideal gases? Compressible flows...

ghost82 February 5, 2015 05:34
If you have the static pressure at inlet you can go for trials and errors to get a correct velocity inlet.
Moreover, if you know velocity at inlet and you know the properties of the liquid, then you know also the mass flow inlet.

It should be applied to gases also.

amin.z February 5, 2015 05:37
Quote:
Originally Posted by ghost82 (Post 530514)
If you have the static pressure at inlet you can go for trials and errors to get a correct velocity inlet.
Moreover, if you know velocity at inlet and you know the properties of the liquid, then you know also the mass flow inlet.

It should be applied to gases also.
Good! You're right!
Thanks for benefit help! :)

amin.z February 9, 2015 01:40
Quote:
Originally Posted by ghost82 (Post 530514)
If you have the static pressure at inlet you can go for trials and errors to get a correct velocity inlet.
Moreover, if you know velocity at inlet and you know the properties of the liquid, then you know also the mass flow inlet.

It should be applied to gases also.
"The use of outflow boundary condition is not appropriate for
a compressible flow problem. Please change the zone
types of all outflow boundaries." Fluent said!

ghost82 February 9, 2015 08:21
Yes, outflow is not valid for compressible flow (sorry I didn't read your gas was compressible).


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