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

Karman vortex street

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 18, 2002, 22:18
Default Karman vortex street
  #1
Zhipeng
Guest
 
Posts: n/a
Hi, everybody.

I have a trouble with the calculation of the Karman vortex street. It is a problem of flowing over a cylinder. The parameters that I used in Fluent(2D Segregated) are listed below: ++++++++++++++++++++++++++++++++++++++++++++++++++ +++++

The size of domain :length:40m width:15m

The diameter of cylinder :2m

The location of cylinder 15,7.5)

Boundary conditions :

left boundary -- Velocity Inlet

right boundary -- Pressure Outlet

top and bottom boundary -- Wall

cylinder -- Wall

The properties of air :density:1.225kg/m3

viscosity:1.7894e-05kg/m-s

X-Velocity in Velocity Inlet :7.3037e-04m/s (constant),so Re=100.

Viscous Model :Laminar

Time step size :0.01s

Number of Time steps :20000 ++++++++++++++++++++++++++++++++++++++++++++++++++ +++++

But I did not see the Karman vortex street. What shall I do? Please give me some advice, thanks a lot.
  Reply With Quote

Old   June 19, 2002, 05:17
Default Re: Karman vortex street
  #2
Laika
Guest
 
Posts: n/a
try wather instead of air

use realizable k-eps-turbulence-model instead of laminar flow.

good luck,

Laika, still orbiting
  Reply With Quote

Old   June 19, 2002, 21:46
Default Re: Karman vortex street
  #3
Zhipeng
Guest
 
Posts: n/a
I have done the calculation with your method, but it doesn't work. Any suggestions?
  Reply With Quote

Old   June 19, 2002, 22:52
Default Re: Karman vortex street
  #4
Steve
Guest
 
Posts: n/a
At that low reynolds number the flow may be steady. Either perturb the flow with asymmetric initial conditions. Or try a slightly higher Reynolds number. From memory I think it is more like Re=300 when the vortex street develops.

Don't use a turbulence model because the flow isn't turbulent and turbulence with just damp unsteadyness.

Steve
  Reply With Quote

Old   June 20, 2002, 01:04
Default Re: Karman vortex street
  #5
Jin-Wook LEE
Guest
 
Posts: n/a
Anyway, at first, I think that you should try to give pertubation to the steady solution to see the unsteady flow. Otherwise, even though the flow is unsteady, you can see the unsteady flow after (maybe) couple of millions time step, at which time, numerical truncation error can be 'artificial pertubation.

Sincerely, Jinwook

  Reply With Quote

Old   June 24, 2002, 12:00
Default Re: Karman vortex street
  #6
Jeff Moder
Guest
 
Posts: n/a
Besides the other comments on making sure you start your time-accurate simulation from some "perturbed" state, you may also want to increase your time step to something larger that 0.01 s, such as 16 sec.

I say increase your time step based on the following:

Let time setp dt = (period of lift)/1000

(actually even a few hundred time steps per period is probably enough, but 1000 should be plenty).

period of lift = 1/freq = D/(U * St)

D = cylinder diameter = 2 m U = uniform inlet speed = 7.3037e-04 m/s St = Strouhal number = 0.165 for Re=100 cylinder

period of lift = 1.66e+04 sec

dt = 1.55e+04/1000 = 16.6 sec

  Reply With Quote

Reply


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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
karman vortex street help please SSeth STAR-CCM+ 7 January 10, 2011 12:31
von Karman vortex street. Vortices formation mechanism. mnvl Main CFD Forum 1 February 24, 2010 18:53
Karman vortex street ??? anisa FLUENT 1 May 5, 2005 14:04
Kármán vortex street in cavitating flow behind bodies in the cavitation tunnel L. Könözsy Main CFD Forum 0 April 17, 2000 14:16
Kármán vortex street (article)? Vortexstr Main CFD Forum 0 February 9, 2000 07:47


All times are GMT -4. The time now is 15:39.