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

problem about a periodic moving wall

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 28, 2013, 18:17
Default problem about a periodic moving wall
  #1
Member
 
jiaqi wang
Join Date: Jan 2013
Posts: 36
Rep Power: 4
itsqi7 is on a distinguished road
Hi guys,

I tried to test my UDF in a simple conical chamber and defined one under-surface as a moving wall using UDF.
But when I review the speed of this moving wall after more than one period simulation. The velocity of this wall did not fit the function defined in UDF.
Does that mean I can't simply assign this UDF to a wall? Can anyone told me is there anything I missed?
My UDF is as following:

#include "udf.h"
#define OMEGA 10.0 /* User constants can be set like this */
#define V_AMP 5.0

DEFINE_PROFILE(y_velocity, ft, var)
{
real flow_time;
face_t f; /* Face index has its own type */

flow_time = CURRENT_TIME; /* Special Fluent macro */

begin_f_loop(f,ft) /* Fluent has special face loop macros too */
{
F_PROFILE(f,ft,var) =-V_AMP * cos(OMEGA*flow_time);
}
end_f_loop(f,ft)
}


Regards,
itsqi7
itsqi7 is offline   Reply With Quote

Old   January 29, 2013, 02:47
Default
  #2
Senior Member
 
Paritosh Vasava
Join Date: Oct 2012
Location: Lappeenranta, Finland
Posts: 544
Rep Power: 12
vasava will become famous soon enough
I am not sure it works but you can try this.

Instead of

begin_f_loop(f,ft) /* Fluent has special face loop macros too */

try

if (CURRENT_TIME>=0 && ... CURRENT_TIME>=time_period)
vasava is offline   Reply With Quote

Old   January 29, 2013, 16:34
Default
  #3
Member
 
jiaqi wang
Join Date: Jan 2013
Posts: 36
Rep Power: 4
itsqi7 is on a distinguished road
Quote:
Originally Posted by vasava View Post
I am not sure it works but you can try this.

Instead of

begin_f_loop(f,ft) /* Fluent has special face loop macros too */

try

if (CURRENT_TIME>=0 && ... CURRENT_TIME>=time_period)
Hi Vasava,

Thanks for ur reply. What I found is that I have to use dynamic meshing so that the moving wall won't be 'fixed'.
Could you pls tell me what is the function of ur code and what is '...' mean?

Thanks,
itsqi7
itsqi7 is offline   Reply With Quote

Old   January 30, 2013, 02:44
Default
  #4
Senior Member
 
Paritosh Vasava
Join Date: Oct 2012
Location: Lappeenranta, Finland
Posts: 544
Rep Power: 12
vasava will become famous soon enough
Hello

'...' means nothing. You can put whatever logical condition you want to use.

By the way I could think of two methods to tackle the problem you have.

1. I would create my domain with wall having small thickness. Make sure that the wall appears as separate zone.

Then go to Cell Zone Condition>Wall Zone ('Wall Zone is illustrative name. Your can name the wall whatever you want to').

Then activate 'Mesh Motion'

Then use UDF for zone motion function.

2. Go to boundary conditions and open the wall window. Then select 'moving wall'. Then select 'Components'. Now you can use UDF for x-velocity, y-velocity and z-velocity.

You can use geometry without wall for this method.


All the best.
vasava is offline   Reply With Quote

Old   January 30, 2013, 17:20
Default
  #5
Member
 
jiaqi wang
Join Date: Jan 2013
Posts: 36
Rep Power: 4
itsqi7 is on a distinguished road
Quote:
Originally Posted by vasava View Post
Hello

'...' means nothing. You can put whatever logical condition you want to use.

By the way I could think of two methods to tackle the problem you have.

1. I would create my domain with wall having small thickness. Make sure that the wall appears as separate zone.

Then go to Cell Zone Condition>Wall Zone ('Wall Zone is illustrative name. Your can name the wall whatever you want to').

Then activate 'Mesh Motion'

Then use UDF for zone motion function.

2. Go to boundary conditions and open the wall window. Then select 'moving wall'. Then select 'Components'. Now you can use UDF for x-velocity, y-velocity and z-velocity.

You can use geometry without wall for this method.


All the best.
Thanks so much for ur reply.
Since my model is similar to a piston in an cylinder, do I need to use dynamic meshing?

Regards,
itsqi7
itsqi7 is offline   Reply With Quote

Old   January 31, 2013, 07:15
Default
  #6
Senior Member
 
Paritosh Vasava
Join Date: Oct 2012
Location: Lappeenranta, Finland
Posts: 544
Rep Power: 12
vasava will become famous soon enough
I do not know much about your experiments and so can not comment on weather you need dynamic mesh or now. Also I have not done any piston-cylinder simulations.

Based on my experience I just wanted to let you know how you could use moving mesh and moving frame of reference.
vasava is offline   Reply With Quote

Old   January 31, 2013, 16:54
Default
  #7
Member
 
jiaqi wang
Join Date: Jan 2013
Posts: 36
Rep Power: 4
itsqi7 is on a distinguished road
Quote:
Originally Posted by vasava View Post
I do not know much about your experiments and so can not comment on weather you need dynamic mesh or now. Also I have not done any piston-cylinder simulations.

Based on my experience I just wanted to let you know how you could use moving mesh and moving frame of reference.
Actually, I'm new to FLUENT.
Anyway, thank you so much. I'll try your advice later.

Regards,
itsqi7
itsqi7 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
mergeMeshes problem Attesz OpenFOAM Mesh Utilities 2 December 14, 2013 09:19
Fluent3DMeshToFoam simvun OpenFOAM Other Meshers: ICEM, Star, Ansys, Pointwise, GridPro, Ansa, ... 48 May 14, 2012 05:20
Wall formation problem in 3D geometry subha_meter Main CFD Forum 0 July 23, 2010 03:46
Errors running allwmake in OpenFOAM141dev with WM_COMPILE_OPTION%3ddebug unoder OpenFOAM Installation 11 January 30, 2008 21:30
moving wall BC problem Sourabh Main CFD Forum 1 August 8, 2006 07:47


All times are GMT -4. The time now is 10:43.