# Von Karman 2D Stable, no shedding

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

 March 10, 2004, 06:43 Von Karman 2D Stable, no shedding #1 Stephen Mar Guest   Posts: n/a I am trying to simulate the shedding of Von Karman Vortices from a 2d cylinder. However I am only seeing steady no shedding results. I have read the posting on this site, which appear to indicate that a disturbance is required before the unsteady result will be achieved. If this is the case could someone give me an Idea of what disturbance is required and how I could go about it. Cheers!! in advance!! The problem is set up as follows Re = 70 V = 0.001 D = 1 Fluid = Air Domain is ten cords with Circular shaped Velocity inlet, and velocity outlet (No external walls) Model = Laminar Time step = 0.00001 Have tried altering the relaxation factors Cheers!! in advance!!

 March 10, 2004, 11:13 Re: Von Karman 2D Stable, no shedding #2 paul Guest   Posts: n/a Stephen If you have a look at the validations that are posted up on the Fluent website for Fluent 6.0, there is a validation that uses the vortex shedding around a cylinder. They give details about the disturbance required to initiate the vortex street. Hope this helps Paul

 March 10, 2004, 17:46 Re: Von Karman 2D Stable, no shedding #3 Manuel Guest   Posts: n/a Hi Stephen The use of a disturbance may not be necessary. At least I runned this flow test some time ago for Re=100, and obtained the transient flow with good accuracy. If your mesh is coarse or you are using first order upwind for the discretization of convective terms you may not obtain the shedding as expected. Try using QUICK in the discretization of convection. I think it will be enough (Solve->Controls->Solution->Momentum->QUICK). Of course you should use the unsteady solver, preferably with second order accuracy. Your time step should also be well chosen. For Re=70 -> Strouhal = 0.15 (approx) so: T (period) =1/f=D/(U*0.15)=1/(0.001*0.15)=6670 s So using dt=1E-=5 you will need 667000000 time steps per shedding cicle !!! You should use a time step of order of T/100, i.e. around 5 sec. Hope this help, Cheers Manuel

 March 16, 2004, 15:48 Re: Von Karman 2D Stable, no shedding #4 Stephen Mar Guest   Posts: n/a Thanks! Paul and Manual, The help was much appreciated Cheer!!!!!!

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post quarkz Main CFD Forum 1 August 20, 2009 15:15 openTom OpenFOAM Installation 4 May 3, 2009 14:44 Kristine FLUENT 0 March 11, 2004 12:50 Mahdy Karzar Jeddy FLUENT 1 August 11, 2002 22:25 Txingurri Main CFD Forum 0 May 2, 2002 12:05

All times are GMT -4. The time now is 23:41.