CFD Online URL
[Sponsors]
Home > Forums > FLUENT

Oscillation airfoil in infinite water depth

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 30, 2013, 23:30
Default Oscillation airfoil in infinite water depth
  #1
New Member
 
Lee,Dong Beom
Join Date: Apr 2013
Posts: 21
Rep Power: 3
ldb83 is on a distinguished road
Hello~ I am a beginner for FLUENT.
Now I am simulating the oscillation airfoil in infinite water depth.
I used pressure-based and UDF for the motion of oscillation.
also standard k-e model is used for the model.
water flow from left boundary with 2.0 m/sec^2 and the frequency of body oscillation is 5Hz.

Question

1. I give no slip condition to the upper and lower wall to consider infinite water depth. I am not sure it is enough or not? Should I give additional consideration to the boundary?

2. I am wondering standard k-e model is suitable for this kind of simulation.

Have a nice day all of you~
Attached Images
File Type: jpg airfoil.JPG (58.2 KB, 23 views)
File Type: jpg airfoil2.JPG (72.1 KB, 20 views)
File Type: jpg airfoil3.JPG (51.3 KB, 23 views)
ldb83 is offline   Reply With Quote

Old   May 31, 2013, 05:39
Default
  #2
New Member
 
Stefanos Katifeoglou
Join Date: Oct 2011
Location: Athens, Greece
Posts: 19
Rep Power: 5
stefanos is on a distinguished road
for infinite boundaries, and more specifically, for solutions that require the viscous fluid not to reflect on the boundary, i think that the "pressure farfield" condition is a more suitable option, however it's setting up is a bit more complex than the other BCs. I haven't worked on it so i can't tell you more. You can check out the manual on that.
stefanos is offline   Reply With Quote

Old   May 31, 2013, 05:42
Default
  #3
New Member
 
Stefanos Katifeoglou
Join Date: Oct 2011
Location: Athens, Greece
Posts: 19
Rep Power: 5
stefanos is on a distinguished road
Quote:
Originally Posted by stefanos View Post
for infinite boundaries, and more specifically, for solutions that require the viscous fluid not to reflect on the boundary, i think that the "pressure farfield" condition is a more suitable option, however it's setting up is a bit more complex than the other BCs. I haven't worked on it so i can't tell you more. You can check out the manual on that.
however, as long as the oscillation amplitude of your airfoil is not extreme, for your domain i don't think that you'll have any problem retaining the no-slip BCs
stefanos is offline   Reply With Quote

Old   May 31, 2013, 18:43
Default
  #4
Senior Member
 
Lefteris
Join Date: Oct 2011
Location: UK, Greece
Posts: 186
Rep Power: 5
Aeronautics El. K. is on a distinguished road
1. m/s^2 are units for acceleration, not for velocity, right?
2. There are 2 papers titled "Evaluation of turbulence models for unsteady flows of an oscillating airfoil" by Srinivasan, Ekaterinaris and McCroskey and "computation of separated and unsteady flows with one- and two- equation models by Ekaterinaris and Menter, which could answer your questions about the turbulence model.
__________________
Lefteris

Aeronautics El. K. is offline   Reply With Quote

Old   May 31, 2013, 21:05
Default
  #5
New Member
 
Lee,Dong Beom
Join Date: Apr 2013
Posts: 21
Rep Power: 3
ldb83 is on a distinguished road
Thank you for your kind reply. It will be very useful for my simulation~

1. It's my mistake. I have used m/s for velocity.
2. I will review the papers mentioned by you.
ldb83 is offline   Reply With Quote

Old   May 31, 2013, 21:05
Default
  #6
New Member
 
Lee,Dong Beom
Join Date: Apr 2013
Posts: 21
Rep Power: 3
ldb83 is on a distinguished road
Quote:
Originally Posted by Aeronautics El. K. View Post
1. m/s^2 are units for acceleration, not for velocity, right?
2. There are 2 papers titled "Evaluation of turbulence models for unsteady flows of an oscillating airfoil" by Srinivasan, Ekaterinaris and McCroskey and "computation of separated and unsteady flows with one- and two- equation models by Ekaterinaris and Menter, which could answer your questions about the turbulence model.
Thank you for your kind reply. It will be very useful for my simulation~

1. It's my mistake. I have used m/s for velocity.
2. I will review the papers mentioned by you.
ldb83 is offline   Reply With Quote

Old   May 31, 2013, 21:11
Default
  #7
New Member
 
Lee,Dong Beom
Join Date: Apr 2013
Posts: 21
Rep Power: 3
ldb83 is on a distinguished road
Quote:
Originally Posted by stefanos View Post
for infinite boundaries, and more specifically, for solutions that require the viscous fluid not to reflect on the boundary, i think that the "pressure farfield" condition is a more suitable option, however it's setting up is a bit more complex than the other BCs. I haven't worked on it so i can't tell you more. You can check out the manual on that.
Thank you for your kind reply. Can I add one more questions?
I have seen some simulation using pressure-outlet to consider infinite depth.
Do you think that pressure-outlet condition is more suitable than no-slip condition??
ldb83 is offline   Reply With Quote

Old   June 1, 2013, 06:51
Default
  #8
Senior Member
 
Lefteris
Join Date: Oct 2011
Location: UK, Greece
Posts: 186
Rep Power: 5
Aeronautics El. K. is on a distinguished road
May I ask what exactly do you mean by "infinite water depth"?

I believe there's not such thing. Water depth is finite and max depth is somewhere in the Pacific and counts about 11km.

The no-slip condition doesn't define the depth. Neither does so the pressure outlet.
I think that the depth should be defined via the operating pressure.
__________________
Lefteris

Aeronautics El. K. is offline   Reply With Quote

Old   June 2, 2013, 02:05
Default
  #9
New Member
 
Lee,Dong Beom
Join Date: Apr 2013
Posts: 21
Rep Power: 3
ldb83 is on a distinguished road
Quote:
Originally Posted by Aeronautics El. K. View Post
May I ask what exactly do you mean by "infinite water depth"?

I believe there's not such thing. Water depth is finite and max depth is somewhere in the Pacific and counts about 11km.

The no-slip condition doesn't define the depth. Neither does so the pressure outlet.
I think that the depth should be defined via the operating pressure.
It means that any boundary condition is not considered in my simulation.
so I would like to consider only the effect from oscillating airfoil.

If the airfoil is oscillated in shallow water depth, there is some wave reflection from bottom boundary. however In my simulation, I don't want to consider that kind of effect.

so now I am little bit confusing should I define the upper and lower wall as pressure-out.

I am not sure my interpretation is enough or not.
ldb83 is offline   Reply With Quote

Old   June 2, 2013, 07:15
Default
  #10
Senior Member
 
Lefteris
Join Date: Oct 2011
Location: UK, Greece
Posts: 186
Rep Power: 5
Aeronautics El. K. is on a distinguished road
Hello Lee!

I just noticed at the pictures you uploaded that the inlet and outlet boundaries are only 12m apart while your airfoil's chord is 1m. It is quite probable then, that the boundaries will influence the solution that's why you should increase this distance.

I guess that by "upper and lower wall" you mean, actually, the upper and lower boundaries of your domain. In this case, I think you should do what Stefanos suggested and define them as pressure far-field.
__________________
Lefteris

Aeronautics El. K. is offline   Reply With Quote

Old   June 2, 2013, 07:59
Default
  #11
New Member
 
Lee,Dong Beom
Join Date: Apr 2013
Posts: 21
Rep Power: 3
ldb83 is on a distinguished road
Quote:
Originally Posted by Aeronautics El. K. View Post
Hello Lee!

I just noticed at the pictures you uploaded that the inlet and outlet boundaries are only 12m apart while your airfoil's chord is 1m. It is quite probable then, that the boundaries will influence the solution that's why you should increase this distance.

I guess that by "upper and lower wall" you mean, actually, the upper and lower boundaries of your domain. In this case, I think you should do what Stefanos suggested and define them as pressure far-field.
Mr. Lefteris~
Thank you so much your recommendation.
I was thinking the distance is too short compared to chord length.
so I am planing to increase the domain length as 40 times of chord length.
also the upper and lower boundary is changed to pressure-outlet.
I think that It could be also reasonable boundary condition compared to pressure far field.
anyway Many thanks~
ldb83 is offline   Reply With Quote

Old   June 2, 2013, 08:06
Default
  #12
Senior Member
 
Lefteris
Join Date: Oct 2011
Location: UK, Greece
Posts: 186
Rep Power: 5
Aeronautics El. K. is on a distinguished road
You're right. A little revision in fluent's user's guide helps.
Pressure outlet is the general condition... Pressure far field is recommended for compressible flow. I was wrong on that, sorry.
__________________
Lefteris

Aeronautics El. K. is offline   Reply With Quote

Old   June 3, 2013, 03:09
Default
  #13
New Member
 
Lee,Dong Beom
Join Date: Apr 2013
Posts: 21
Rep Power: 3
ldb83 is on a distinguished road
Quote:
Originally Posted by Aeronautics El. K. View Post
You're right. A little revision in fluent's user's guide helps.
Pressure outlet is the general condition... Pressure far field is recommended for compressible flow. I was wrong on that, sorry.
Thank you so much for you comment.
Your comment was very valuable for my simulation.
Have a nice day~
ldb83 is offline   Reply With Quote

Old   June 4, 2013, 08:25
Default
  #14
New Member
 
mohammed ibrahim
Join Date: May 2013
Posts: 2
Rep Power: 0
mhmmad_ibraham is on a distinguished road
Hello sir...
please send me your udf of oscillation motion as fast as you can...
my E_mail is m70hm@yahoo.com
mhmmad_ibraham is offline   Reply With Quote

Old   June 4, 2013, 09:03
Default
  #15
New Member
 
Nitish Singh
Join Date: May 2013
Location: India
Posts: 17
Rep Power: 3
nitman118 is on a distinguished road
Send a message via Yahoo to nitman118
hi,
can you share your udf with me....it will be really helpful,thanks.....
id: nitman118@gmail.com
nitman118 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
Problem with restart solution in shape_optimization.py robyTKD SU2 Shape Design 21 May 29, 2013 10:26
Water subcooled boiling Attesz CFX 7 January 5, 2013 04:32
dynamic mesh airfoil oscillation aamer Fluent UDF and Scheme Programming 0 January 25, 2011 08:29
Terrible Mistake In Fluid Dynamics History Abhi Main CFD Forum 12 July 8, 2002 10:11
uptodate water distribution network fredius,magige,tanzanian,(e.a) Main CFD Forum 0 January 27, 2002 08:10


All times are GMT -4. The time now is 23:10.