CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

reverse flow

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 10, 2001, 11:50
Default reverse flow
  #1
Giovanni
Guest
 
Posts: n/a
Hello,

I'm analyzing a particular blower. The fluid is air and it is ideal-gas. The inflow section and the outflow section have the same size. The fluid flow presents a swirl at outflow due to the particular blower. Velocity near the delivery is greater than velocity at the in-flow. Boundary conditions are: mass-flow-inlet and pressure outlet.

I've already elongated the delivery piping, but there is a reverse flow the same at the centre of outflow surface.

What do I have to do?

Thank you Giovanni
  Reply With Quote

Old   October 11, 2001, 02:52
Default Re: reverse flow
  #2
hvn
Guest
 
Posts: n/a
Perhaps, put away your outlet with an extrusion.
  Reply With Quote

Old   October 11, 2001, 13:07
Default Re: reverse flow
  #3
Chetan Kadakia
Guest
 
Posts: n/a
I'm sorry, I don't understand what is meant by "put away your outlet with an extrusion". Could you clarify that Giovani?

  Reply With Quote

Old   October 11, 2001, 14:12
Default Re: reverse flow
  #4
Steven Smith
Guest
 
Posts: n/a
I'm not familiar with blowers, so my question might be off-base. Have you considered the possibility that given your swirling outflow, that a reversed flow through your pressure outlet might be real?
  Reply With Quote

Old   October 12, 2001, 02:45
Default Re: reverse flow
  #5
hvn
Guest
 
Posts: n/a
I mean that maybe the outlet is to close to the particle blower. So you must increase your calculation domain. For that, you need to increase the length of your inlet pipe. One other solution is to increase the mesh density at the outlet because the mesh is too coarse at this location.
  Reply With Quote

Old   October 12, 2001, 03:01
Default Re: reverse flow
  #6
Giovanni
Guest
 
Posts: n/a
Yes Steven,

this is my doubt. Infact the reverse flow is at the centre of the pressure outlet surface.

Thank you Giovanni
  Reply With Quote

Old   October 12, 2001, 03:05
Default Re: reverse flow
  #7
Giovanni
Guest
 
Posts: n/a
Why if the outlet is to close to the particle blower I have to increase the length of inlet pipe? What are the changes?

Thank you Giovanni
  Reply With Quote

Old   October 12, 2001, 03:37
Default Re: reverse flow
  #8
hvn
Guest
 
Posts: n/a
Sorry, I would say outlet pipe.
  Reply With Quote

Old   October 12, 2001, 07:18
Default Re: reverse flow
  #9
Alain
Guest
 
Posts: n/a
As a matter of fact reverse flow at outlet are often seen in blower simulation.

You are perfectly right when you doubt of the physical or numerical origin for this feature (I saw both).

First of all, about the physical cause, it depend of the kind of blower you have. if it is an axial one : if your rotation speed is very high you can have a very strong pressure gradient due to swirl which cause a "vortex breakdown" and then a reverse flow.

among the possible numerical causes of this feature you have :

Too coarse mesh (flow in a blower generally need a fine mesh with a good resolution at wall)

Ill posed boundary condition

An outlet too close to the fan wheel.

etc...

For example, you can try Total pressure inlet/static pressure outlet instead of massflow (beside, I think that the massflow inlet in fluent is suitable for compressible gaz only and can give convergence trouble).

You can also try to refine your mesh.

Best regards

alain

  Reply With Quote

Old   October 12, 2001, 08:40
Default Re: reverse flow
  #10
Giovanni
Guest
 
Posts: n/a
In my particular case, the flow turns around a core before to go out of the blower and this causes the swirl.

The compression ratio is 1.21.

May you explain "vortex breakdown"?

Thanks a lot Giovanni

  Reply With Quote

Old   October 12, 2001, 14:56
Default Re: reverse flow
  #11
stephen
Guest
 
Posts: n/a
In order to know if the real flow is also reverse flow,maybe you'd better calcuate the off-design points,i.e.different compression ratio and mass flow at the same rotating speed. For lower pressure ratio and larger mass flow, the flow will be less possible reverse and perhaps reverse flow will disappear.
  Reply With Quote

Old   October 15, 2001, 03:01
Default Re: reverse flow
  #12
Giovanni
Guest
 
Posts: n/a
Ok, thank you Stephen, I'll try it.

Giovanni
  Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Reverse flow e101533 Siemens 9 April 5, 2020 02:29
Reverse Flow Bharati FLUENT 0 September 14, 2010 01:09
Flow simulation in reverse drum mixer Patel Chirag CFX 0 July 19, 2010 15:05
reverse flow alikami FLUENT 1 June 2, 2010 04:19
Reverse flow in the VOF model yan FLUENT 1 May 26, 2005 09:14


All times are GMT -4. The time now is 10:27.