[mariam.sara]

Hello I have a query to how i can make the inlet velocity value fixed from pipe inlet until pipe outlet? is that possible in Fluent? knowing that the flow is laminar?

Mariam

[mariam.sara]

No one know how to answer my question?

[flotus1]

You could write a macro that patches the velocity at the beginning of every iteration.
But I am really curious what the application for such a "boundary" condition could be.

[kad]

I gues you want to model fully developed flow. Try periodic boundary condition for inlet and outlet with specified mass flow http://aerojet.engr.ucdavis.edu/flue...g/node1355.htm .

[mariam.sara]

Hi Flotus thanks a lot for the answer. I need to ask did you have any tutorial about using macro within boundary conditions? I did not use this method before?

mariam

Originally Posted by flotus1

You could write a macro that patches the velocity at the beginning of every iteration.
But I am really curious what the application for such a "boundary" condition could be.

[zombiaska]

I haven't tried this idea only read in manuals. Try putting inlet velocity at outflow place. I mean, have 2 inlet velocities. That inlet velocity which is is on the end give negative value. Like inlet 1 m/s and outlet -1 m/s.

[mariam.sara]

No i do not think this method is accurate because it give reverse flow error.

[QUOTE=zombiaska;474383]I haven't tried this ide a only read in manuals. Try putting inlet velocity at outflow place. I mean, have 2 inlet velocities. That inlet velocity which is is on the end give negative value. Like inlet 1 m/s and outlet -1 m/s.[/QUOTE]

[flotus1]

If you told us what you want to simulate it would be much easier to give a helpful answer. I still dont get why one would want to enforce a constant velocity throughout the domain.

[mariam.sara]

Hello flotus thanks again for the answer. I want to do a pipe flow problem with constant heat flux at the wall I want to prove that Nusselt number is equal to 4.36 hence I need a fully developed flow from the inlet of the pipe until outlet in other word i do not want any increment in inlet velocity happen?

Originally Posted by flotus1

If you told us what you want to simulate it would be much easier to give a helpful answer. I still dont get why one would want to enforce a constant velocity throughout the domain.

[flotus1]

Now that is a completely different situation than "i want a constant velocity from inlet to outlet".
Take a look at the tutorial "Modeling periodic flow and heat transfer"

[mariam.sara]

Well i will look through it but did you think it will fulfill my case if i follow its procedure and give me the correct nusselt number?

Originally Posted by flotus1

Now that is a completely different situation than "i want a constant velocity from inlet to outlet".
Take a look at the tutorial "Modeling periodic flow and heat transfer"

[flotus1]

Of course you will have to transfer some of the techniques introduced in this tutorial to apply to your case. But a periodic flow is the only feasible way to simulate the Nusselt number of a fully developed flow.
Combine this with the advice you got in your other thread about Nusselt numbers in Fluent.

[mariam.sara]

I have ANSYS FLUENT 14 I cannot find periodic conditions under define menu? where i can find this option?

Originally Posted by flotus1

Of course you will have to transfer some of the techniques introduced in this tutorial to apply to your case. But a periodic flow is the only feasible way to simulate the Nusselt number of a fully developed flow.
Combine this with the advice you got in your other thread about Nusselt numbers in Fluent.

[flotus1]

Do the tutorial that comes with your fluent installation or type the name of the tutorial in a search engine and take one that is for your fluent version.

[mariam.sara]

I found the tutorial i start with its steps but when i reach applying periodic conditions step to apply the mass flowrate i did not see this option in my define menu hope you understand what i mean now for more illustration see the picture i sent with this post.

Originally Posted by flotus1

Do the tutorial that comes with your fluent installation or type the name of the tutorial in a search engine and take one that is for your fluent version.

[flotus1]

I dont know which tutorial you are using.
The one I am talking about looks like this when it comes to impose a mass flow rate:
periodic.png

[mariam.sara]

Yes it appear after i define the zones in modify zones in fluent console. Now I run this tutorial and I need to apply periodic to my case I have 3D cylinder (pipe) do I need first to transform inlet and outlet boundaries to walls so i can transform it to periodic boundaries?

[flotus1]

No you dont have to do that.
Periodic boundaries can be set up from any kind of boundaries using the text command from the tutorial.

[mariam.sara]

Well I transform inlet boundary to periodic and i made its shadow the outlet boundary it told me periodic zone created and outlet boundary deleted?? when i did run i predict surface heat transfer coefficient from Report integrals for the wall then estimate Nu from the relation Nu=hD/k it become 0.0274 W/m2.K which it incorrect? it should be 4.36?

Originally Posted by flotus1

No you dont have to do that.
Periodic boundaries can be set up from any kind of boundaries using the text command from the tutorial.