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## Simulation CFD

Active Member
Posts: 6
Registered: ‎02-05-2013

# Design only stream or with pipe

171 Views, 7 Replies
02-05-2013 07:04 AM

Hi,

I need confirmation for the following.

For example if i wat to design a simple pipe with a water stream, should i draw only the water stream (considering the inner diameter of the pipe) or the pipe and the water as a solid cylinder with the same length of the pipe?

1. If i draw both, does it calculates the pressure drop in function of the pipe material?

2. If i draw only the water stream, i must define the boundary conditions, correct? Is it possible to define friction factor, dor example?

Thanks!

Product Support
Posts: 936
Registered: ‎08-25-2011

# Re: Design only stream or with pipe

02-06-2013 10:40 AM in reply to: mfqdias

Hi,

It does not matter if you draw the external pipe - you only need it if you wish to look at heat transfer through it.

You can apply a wall roughness to the fluid if you do not model the solid (this is in the material setting)

Either way you will need Boundary Conditions (flow rate at the inlet and a pressure at the outlet for examle).

Jon Wilde
Active Member
Posts: 6
Registered: ‎02-05-2013

# Re: Design only stream or with pipe

02-06-2013 03:59 PM in reply to: mfqdias

Hi,

When you say boundary conditions you didn't refer the perimeter of the cylinder that represents the water stream, but shouldn't this be mentioned?

Ok, so even if i draw the pipe outside the water stream and define the material, should i define the boundary condition of the outer perimeter of the cylinder that represents the stream?

Thanks

Distinguished Contributor
Posts: 141
Registered: ‎06-13-2012

# Re: Design only stream or with pipe

02-06-2013 06:56 PM in reply to: mfqdias

If I understand correctly, what you define as 'perimeter of the cylinder' is the 'curved surface of the cylinder', no?

If that is the case, then the answer is no, you have to specify the flow boundary conditions (eg: flow rate, pressure, etc) at the inlet and outlet of your stream (the flat surfaces of your cylinder) regardless of whether you have your pipe modelled or not. The software then treats fluid surfaces which do not have any flow boundary conditions as walls (0 velocity). Therefore, you do not have to apply any flow boundary conditions on the curved surface of your cylinder, with or without your pipe modelled... assuming this is a regular pipe.

Regards

Ilyas

Product Support
Posts: 936
Registered: ‎08-25-2011

# Re: Design only stream or with pipe

02-06-2013 09:43 PM in reply to: ilyas

Thanks Ilyas

Jon Wilde
Active Member
Posts: 6
Registered: ‎02-05-2013

# Re: Design only stream or with pipe

02-07-2013 02:14 AM in reply to: mfqdias

Ok,

I understand that. The wall velocity may be consider as 0, but if we look at the pressure at outlet, shouldn't it varies in function of the pipe roughness?

Who this enters into account? Or am i sseng this from the wrong point of view?

Thanks!

Product Support
Posts: 936
Registered: ‎08-25-2011

# Re: Design only stream or with pipe

02-07-2013 02:29 AM in reply to: mfqdias

Hi,

Not the wrong point of view but perhaps not quite within the correct expectations. Please try what we are suggesting and you will find that you are very close to reality I am sure.

It might be worth extending the outlet also (5x diameter is standard).

Jon Wilde
Active Member
Posts: 6
Registered: ‎02-05-2013

# Re: Design only stream or with pipe

02-07-2013 02:33 AM in reply to: wildej

Ok i understand.

Thank you all for the help!