CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

inlet has higher pressure than outlet in axial flow fan

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 18, 2012, 05:36
Default
  #21
Member
 
Aathavan
Join Date: Nov 2012
Posts: 70
Rep Power: 4
Aadhavan is on a distinguished road
Hi Vicarious,
thanks for the reply, i have asked that information just for clarification.
I have tried to run the case, but it giving fatal error as follows,

--> FOAM FATAL IO ERROR:
Cannot find patchField entry for cyclic ILR0
Is your field uptodate with split cyclics?
Run foamUpgradeCyclics to convert mesh and fields to split cyclics.

file: /home/cerecam/OpenFOAM/OpenFOAM-2.0.1/tutorials/incompressible/MRFSimpleFoam/exCompDomain/onlyPressure/0/U::boundaryField from line 25 to line 76.

From function GeometricField<Type, PatchField, GeoMesh>::
GeometricBoundaryField::GeometricBoundaryField
(
const BoundaryMesh&,
const DimensionedField<Type, GeoMesh>&,
const dictionary&
)
in file /home/cerecam/OpenFOAM/OpenFOAM-2.0.1/src/OpenFOAM/lnInclude/GeometricBoundaryField.C at line 271.

FOAM exiting

I dont now how to fix this.

thanks,
Aadhavan
Aadhavan is offline   Reply With Quote

Old   November 19, 2012, 07:09
Default
  #22
Member
 
vicarious's Avatar
 
Pedram Mojtabavi
Join Date: Apr 2011
Location: Iran
Posts: 66
Rep Power: 6
vicarious is on a distinguished road
Send a message via Yahoo to vicarious
Dear Aadhavan,

I'm not familiar with the FAOM errors I'm afraid. Is your mesh fine enough? maybe it's something due to the mesh.
vicarious is offline   Reply With Quote

Old   November 19, 2012, 07:47
Default
  #23
Member
 
Aathavan
Join Date: Nov 2012
Posts: 70
Rep Power: 4
Aadhavan is on a distinguished road
Hi Vicarious,
I hope the mesh is not a problem, because I have done some simulation with the same mesh. Now I have changed only the BC.
I feel mesh wont be a problem.

Thanks Vicarious for your support,
Aadhavan
Aadhavan is offline   Reply With Quote

Old   November 19, 2012, 14:06
Default
  #24
Member
 
vicarious's Avatar
 
Pedram Mojtabavi
Join Date: Apr 2011
Location: Iran
Posts: 66
Rep Power: 6
vicarious is on a distinguished road
Send a message via Yahoo to vicarious
My pleasure, I hope you succeed dear Aadhavan.
vicarious is offline   Reply With Quote

Old   November 19, 2012, 14:57
Default
  #25
Member
 
Aathavan
Join Date: Nov 2012
Posts: 70
Rep Power: 4
Aadhavan is on a distinguished road
Hi Vicarious,
I have done small changes in inlet and outlet. the simulation is going, let us see what is the result tomorrow.

Thanks,
Aadhavan
Aadhavan is offline   Reply With Quote

Old   November 20, 2012, 17:52
Default
  #26
Orb
Member
 
Join Date: Jan 2012
Posts: 52
Rep Power: 5
Orb is on a distinguished road
I am having a misunderstanding on how to apply the boundary conditions to my fan too. For example, ANSYS CFX has boundaries of "openings". Are these the best boundary conditions to use? I do not get velocity in - it shows these as 0 m/s. Is it better to apply a mass flow rate in?
Orb is offline   Reply With Quote

Old   November 21, 2012, 05:34
Default
  #27
Member
 
vicarious's Avatar
 
Pedram Mojtabavi
Join Date: Apr 2011
Location: Iran
Posts: 66
Rep Power: 6
vicarious is on a distinguished road
Send a message via Yahoo to vicarious
Quote:
Originally Posted by Orb View Post
I am having a misunderstanding on how to apply the boundary conditions to my fan too. For example, ANSYS CFX has boundaries of "openings". Are these the best boundary conditions to use? I do not get velocity in - it shows these as 0 m/s. Is it better to apply a mass flow rate in?
Do not use velocity inlet for this type of devices. You need to set the inlet boundary as a fixed total pressure and total temperature. You can also set it as mass flow with inlet static pressure.
vicarious is offline   Reply With Quote

Old   November 28, 2012, 04:36
Default
  #28
Member
 
Aathavan
Join Date: Nov 2012
Posts: 70
Rep Power: 4
Aadhavan is on a distinguished road
Hi Vicarious,
Thanks for your help so for, I found the mistake and fixed it.
the fan was spinning anti-clock wise direction instead of clock wise direction.
I ran the simulation again in clock wise direction, I am getting the reasonable pressure raise, but the pressure raise which I am getting is lower than the experimental result.
the simulation result is 140Pa
experimental result is 225Pa

Can you give me some hit, how can we increase the pressure raise.

I am planning to give slip condition for fan, is ok?

Thanks,
Aadhavan
Aadhavan is offline   Reply With Quote

Old   November 28, 2012, 06:02
Default
  #29
Member
 
vicarious's Avatar
 
Pedram Mojtabavi
Join Date: Apr 2011
Location: Iran
Posts: 66
Rep Power: 6
vicarious is on a distinguished road
Send a message via Yahoo to vicarious
Hi Aadhavan,
Glad to see your simulation running. The experimental validation depends on several reasons and it's not easy to find what the problem might be. I have the same problem with pressure rise validation in my case about axial compressor. The pressure rise in high mass flow regions was lower than the experimental results. The investigation through some papers showed that it's due to the turbulence model used in numerical solution and the errors that may occur through experimental data. Also the blade profiles and the geometry usually can not be matched to the experimental test.
What do you mean slip condition? If you mean the boundary conditions about the walls then why do you want to change it?
vicarious is offline   Reply With Quote

Old   November 28, 2012, 09:09
Default
  #30
Member
 
Aathavan
Join Date: Nov 2012
Posts: 70
Rep Power: 4
Aadhavan is on a distinguished road
Hi Vicarious,
I have seen in Wiki or CFD online, "k-epsilon is inappropriate choice for problem such us compressor" is it applicable for fan as well.
If so which turbulence model I can use or else can switch of the turbulence model.

the slip boundary condition is for fan, due to viscosity the pressure raise may fall down right, that is why I am thinking to give slip BC for fan. ( no viscose effect at fan wall)

Thanks,
Aadhavan
Aadhavan is offline   Reply With Quote

Old   November 28, 2012, 10:35
Default
  #31
Member
 
vicarious's Avatar
 
Pedram Mojtabavi
Join Date: Apr 2011
Location: Iran
Posts: 66
Rep Power: 6
vicarious is on a distinguished road
Send a message via Yahoo to vicarious
Dear Aadhavan, I disagree with such statement that "k-epsilon is inappropriate for simulating fans and compressors". Because there is not a certain way to decide which model could fit the problem. Since I already achieved good results with K-esplion standard and it is appropriate. As you know all the RANS models are not direct solution and not able to predict the turbulent field. Only the DNS models such as LES can directly simulate the eddy viscosity. I have seen several researches that approved K-e, Spalart-Allmaras and the zero-equation Baldwin-Lomax model for these cases and achieved good results. If you are able to consider DNS models, that would be very accurate. If not, the RANS models are also good for these problems.

Regarding the slip boundary, You can not just ignore the viscosity. Any device works with pressure drop due to the viscosity and so as your fan. So ignoring the viscosity is not correct.
vicarious is offline   Reply With Quote

Old   November 28, 2012, 12:03
Default
  #32
Member
 
Aathavan
Join Date: Nov 2012
Posts: 70
Rep Power: 4
Aadhavan is on a distinguished road
Hi Vicarious,
Thanks for the quick and informative reply, I think it is not possible to use DNS for fan simulation in openFOAM. I am not sure about it.


Thanks,
Aadhavan

Last edited by Aadhavan; November 28, 2012 at 12:20.
Aadhavan is offline   Reply With Quote

Old   November 26, 2013, 16:35
Default
  #33
Member
 
Join Date: Aug 2013
Posts: 50
Rep Power: 3
nash is on a distinguished road
hi everyone,
sorry for digging up this thread.

i'm currently doing a simulation of radial fan (sirocco fan) to reproduce the curve of the fan using approach of frozen-rotor.

my question is regarding to BC inlet and outlet for pressure
this simulation is steady state and incompressible.

example for pressure difference of 100pa
i set

the totalpressure as 0 at inlet and staticpressure as -100pa
staticpressure as 0 at outlet.

is it correct?
nash is offline   Reply With Quote

Old   November 27, 2013, 02:41
Default
  #34
Member
 
Aathavan
Join Date: Nov 2012
Posts: 70
Rep Power: 4
Aadhavan is on a distinguished road
Hi There,
I am working on axial fan, I am using mass flow rate inlet and fixedMeanvalue (0) pressure outlet. (OpenFOAM)

Regarding your convergence, try this BC. still if you are not able to get converged solution check your mesh and computational domain.

Thanks,
Aadhavan
Aadhavan is offline   Reply With Quote

Old   November 27, 2013, 02:53
Default
  #35
Member
 
Join Date: Aug 2013
Posts: 50
Rep Power: 3
nash is on a distinguished road
Which turbulence Model are you using?
Could you please share your BC and fvScheme?

Thanks,
Nash
nash is offline   Reply With Quote

Old   July 20, 2014, 12:50
Default axial fan simulation
  #36
Member
 
hashim chaudhry
Join Date: Jun 2014
Location: turkey
Posts: 44
Rep Power: 3
chaudhry_hashim is on a distinguished road
Send a message via Skype™ to chaudhry_hashim
Hi I am working on the simulation of axial fan in order to get the fan curve, in cfd model i made the extruded regions 10 times of fan dia as inlet and outlet. I am using MRF, and i am confused about the inlet and outlet boundary conditions I am giving fixed rpm to the rotating region and i trying with the pressure inlet and outlet BCs but whenever I set outlet pressure as static my solution start diverging too much

I am not able to figuring out the problem how can i get pressure rise across the fan. I have fan curve from the manufacturer.

I would be very grateful if you people help me out.
chaudhry_hashim is offline   Reply With Quote

Old   July 21, 2014, 06:34
Default
  #37
Member
 
Aathavan
Join Date: Nov 2012
Posts: 70
Rep Power: 4
Aadhavan is on a distinguished road
Hi,
I think your BC's are wrong, I am working on axial fan with the following BC's

inlet --> fixedValue or flowRateInletVelocity
outlet --> fixedMeanValue (pressure (0)) or you can try fixedValue but it is not appropriate choice.

Try the above BC's, probably it will fix your problem.

if the problem is still exists,

Check your mesh --> what is your Y+ value??
which turbulence model your are using high or low?

check your initial values of epsilon or omega and k.

as well check your schemes and limiting factors, relaxation factors.

upwind scheme is recommended for epsilon and k,



Thanks,
Aadhavan
Aadhavan is offline   Reply With Quote

Old   July 21, 2014, 08:34
Default hi
  #38
Member
 
hashim chaudhry
Join Date: Jun 2014
Location: turkey
Posts: 44
Rep Power: 3
chaudhry_hashim is on a distinguished road
Send a message via Skype™ to chaudhry_hashim
Thankyou so much I am using 5 prism layer and k-epsilon for this. I tried with the velocity inlet and fixed static pressure (=0) the problem is that total pressure value in upstream is too high and after few iterations (150) reverse flow occur at outlet and the solution is not converging. I am working on STARCCM+ and I have attached pictures of BCs and cfd model. Kindly take a look. The interfaces I am using are inplace interface between the duct and rotating region.
Attached Images
File Type: jpg BCs.jpg (80.6 KB, 0 views)
File Type: jpg fan.jpg (51.7 KB, 2 views)
File Type: jpg geometry.jpg (32.0 KB, 2 views)

Last edited by chaudhry_hashim; July 21, 2014 at 11:11.
chaudhry_hashim is offline   Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Simulation of Axial Fan Flow using A Momentum Source Subdomain Liam CFX 28 July 16, 2013 08:24
How to set up the inlet boundary condition for a low pressure case? beastieboys6 FLUENT 3 April 10, 2012 22:46
pressure inlet & outlet. help ASAP Plz engahmed Main CFD Forum 0 June 13, 2010 15:34
steam flow in a pipe driven by a pressure gradient between inlet and outlet SalvoCalvo Main CFD Forum 0 March 11, 2010 07:52
urgent pressure condition for axial flow fan VIPUL FLUENT 0 October 24, 2008 02:01


All times are GMT -4. The time now is 09:04.