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

Flow over 2D Cylinder, Laminar and Turbulent

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 22, 2011, 19:07
Default Flow over 2D Cylinder, Laminar and Turbulent
  #1
New Member
 
Jon
Join Date: Apr 2011
Posts: 2
Rep Power: 0
Tsr63 is on a distinguished road
Hi,

I am relatively new to CFD and Fluent and I am trying to determine the Drag Force and Drag Coefficient for flow over a 2D cylinder, but I am having some problems with fluent producing the correct value (based on experimental results). First I ran a case for a Reynolds Number of 1,000 and obtained a drag force of .0008 N which is close the the experimental value of .0011 N, but the drag coefficient which should be around 1 is off by a magnitude of 10.

To measure drag force/coefficient I go to Report>Forces>Set X=1,Y=0 and chose the edge which represents the cylinder wall.

When I run a case for a Reynolds number of 100,000 I get a drag force of 2 (should be around 11 N) and a drag coefficient of 314 (which should be around 1). Since the flow is laminar until approximately Re=400,000 for flow around a cylinder, I am using the laminar solver model.

The problem also continues when I try to run a turbulent case using the k-epsilon model.

I created my geometry in gambit. I subtracted a .125 m diameter circle from a larger 2 m diameter circle. I created a sizing function from the edge (or cylinder) to the face. Next I meshed the face using a quad map scheme. This all seems correct to do, but I figured I'd just let you all know in case.

I've tried almost everything I can think of, and even made sure my reference made sense. Any help would be greatly appreciated.

- Jon
Tsr63 is offline   Reply With Quote

Old   May 29, 2011, 20:08
Default
  #2
New Member
 
ojha.mayank485's Avatar
 
Mayank Ojha
Join Date: May 2011
Posts: 22
Rep Power: 6
ojha.mayank485 is on a distinguished road
Quote:
Originally Posted by Tsr63 View Post
Hi,

Since the flow is laminar until approximately Re=400,000 for flow around a cylinder

- Jon

Am very much sure that at such high Re of 400,000, the flow cannot be laminar.
For flow which has circulations, K-e shows delayed separation and hence gives incorrect answers. According to the literature, SST should be what you should be using.
I am trying to simulate a flow over a cylinder at Re=10,000.

Remember: when you are using a turbulent model, make sure your y+ value is acceptable.

Regards,

Mayank
ojha.mayank485 is offline   Reply With Quote

Old   June 3, 2011, 13:48
Default
  #3
Member
 
Join Date: Apr 2011
Posts: 30
Rep Power: 6
skullCFD is on a distinguished road
Did you try a transient simulation? Vortex problems are inherently transient and it helps a lot of times with the solution and convergence issues if you perform a transient simulation. I agree with ojha.mayank485. k-w SST might be good for your case.
skullCFD is offline   Reply With Quote

Old   December 8, 2012, 05:50
Angry flow over two side by side cylinder... with Re100 & 200
  #4
New Member
 
rishitosh's Avatar
 
Rishitosh Ranjan
Join Date: Dec 2012
Location: Trichirapalli, Tamilnadu, India
Posts: 18
Rep Power: 4
rishitosh is on a distinguished road
hiii..

i m also new in dis CFD area...
i m working on flow over two side by side cylinders... @ Re= 100 and 200..
i got good results..

but i want to find out Strouhal number for all cases...

i came to know by finding shedding frequency with help of FFT, using cofficient of lift data, in fluent we can calculate Strouhal number...

but i m getting helpess..

how to use FFT to find shedding frequency....?????
-Rishi
rishitosh is offline   Reply With Quote

Old   December 8, 2012, 06:24
Default
  #5
Senior Member
 
Join Date: Mar 2011
Location: Germany
Posts: 414
Rep Power: 11
cfd seeker is on a distinguished road
Yes try with SST kw and if problem still persists think of trying Transition model.
Note: Search on youtube or in the threads on this forum, I guess "far" has uploaded some videos for the flow simulation on cylinder but i guess those simulations are 3D
cfd seeker is offline   Reply With Quote

Old   November 13, 2014, 13:13
Default
  #6
New Member
 
Steve
Join Date: Dec 2012
Location: Minneapolis
Posts: 7
Rep Power: 4
huxxx088 is on a distinguished road
To use an FFT to calculate Shedding Frequency:

Place a numerical probe somewhere downstream of the cylinder where the flow looks stabilized. Measure the x and y velocity at each timestep and calculate the velocity spectra from that. In the spectra you should see a peak and that will be where your shedding frequency is.


Quote:
Originally Posted by rishitosh View Post
hiii..

i m also new in dis CFD area...
i m working on flow over two side by side cylinders... @ Re= 100 and 200..
i got good results..

but i want to find out Strouhal number for all cases...

i came to know by finding shedding frequency with help of FFT, using cofficient of lift data, in fluent we can calculate Strouhal number...

but i m getting helpess..

how to use FFT to find shedding frequency....?????
-Rishi
huxxx088 is offline   Reply With Quote

Reply

Tags
cylinder, drag, force, turbulent

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
CFX Treatment of Laminar and Turbulent Flows Jade M CFX 6 January 26, 2013 11:11
flow over a cylinder, turbulent and laminar Chetan Kadakia FLUENT 27 December 8, 2012 06:08
Laminar flow or Turbulent flow mech FLUENT 0 January 27, 2007 19:51
2D cylinder, external, laminar and turbulent flow Dave FLUENT 0 December 6, 2006 21:42
modelling laminar and turbulent flow in the same Ol FLUENT 2 November 25, 2005 03:52


All times are GMT -4. The time now is 02:18.