Menu

Discussion Forum

New Discussion
Filter

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

About the stokes drag on a sphere (mph attached)

Posted Sep 12, 2015, 5:03 a.m. EDT Fluid & Heat Version 5.0 4 Replies

Leo Mechelle
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Dear All,

I am trying to find the drag coefficient of a sphere in a stokes flow. Since this 3D problem can be simplified into a 2D problem, I use the creeping flow module in 2D to simulate this case. Attached please find the mph file.
creeping flow BCs: As shown in the attachment, inlet velocity is 10^(-5)m/s, and outlet pressure to be 0. The two side walls are symmetric boundary condition and circle (2d section of sphere) surface velocity to be 0 (no slip).

Then I plot the pressure on the circle and I found it is proportional to cos(theta) (The result is deleted due to the limited attachement size requirement). In theoretical analysis, the form of pressure shound be 3/2*viscosity*velocity*cos(theta)/R^2. Then I check my result and I found the coefficient in front of the cos(theta) is much lower than the theoretical calculation.
And this coefficient becomes lower when I enlarge the simulation box size.

I just wonder if pressure is dependent on box size, can I get a correct result of stokes drag 6*Pi*viscosity*radius*velocity of a sphere using 2D simulation? Should I throw away 2D results and focus on 3D in order to get a correct stokes drag result?

Any help will be greatly appreciated!

Thank you!

Best,
Leo

Attachments:

4 Replies Last Post Jun 24, 2017, 11:16 p.m. EDT
COMSOL Moderator

Hello Leo Mechelle

Your Discussion has gone 30 days without a reply. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help.

If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base.

Ying Tang
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 7 years ago Jun 19, 2017, 1:24 p.m. EDT
Hi Leo,

I am also face the problem of simulation stoke drag on a sphere. Have you solve the issue already?

Best regards,

Ying
Hi Leo, I am also face the problem of simulation stoke drag on a sphere. Have you solve the issue already? Best regards, Ying
Jeff Hiller COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 7 years ago Jun 19, 2017, 2:22 p.m. EDT
Hi Leo,
Since you worked in 2D, your model represents flow around a cylinder, I am afraid.
To model flow around a sphere, you would need to use 2D axisymmetry.
Best regards,
Jeff
Hi Leo, Since you worked in 2D, your model represents flow around a cylinder, I am afraid. To model flow around a sphere, you would need to use 2D axisymmetry. Best regards, Jeff
Leo Mechelle
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 7 years ago Jun 24, 2017, 11:14 p.m. EDT
Dear Jeff,

Thank you so much for your suggestion. It is exactly where my problem lies.

Best Regards,
Leo
Dear Jeff, Thank you so much for your suggestion. It is exactly where my problem lies. Best Regards, Leo
Leo Mechelle
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 7 years ago Jun 24, 2017, 11:16 p.m. EDT
Dear Ying,

Yes. Just set the system to be 2D rotation symmetry as Jeff suggested would solve this problem.

Best Regards,
Leo
Dear Ying, Yes. Just set the system to be 2D rotation symmetry as Jeff suggested would solve this problem. Best Regards, Leo

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content