CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

Problem with vortex shedding frequency

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 26, 2014, 09:20
Default Problem with vortex shedding frequency
  #1
New Member
 
Saravana Kumar Lakshmanan
Join Date: Feb 2013
Posts: 11
Rep Power: 13
aerosaravanan is on a distinguished road
Hi friends,
I am currently trying to simulate flow past a circular cylinder for my thesis in OpenFOAM. I am having problem in getting the correct strouhal number. Drag coefficient is comparatively good. The following are the BC’s and details about mesh
Dia=0.034 m; velocity=20 m/s; Re=45,000 ; Solver- PISOFOAM; RANS Model-kOmegaSST


P-freestreamPressure at inlet & outlet, zeroGradient on cylinder (wall), Symmetry on Top & Bottom


U-freeStreamVelocity at inlet & outlet, fixedValue (0) on wall, Symmetry on Top & Bottom


k-fixedValue at inlet (based on k=3/2(UI)^2),zerogradient at outlet, FixedValue (0) on wall and kqrwallfunction, Symmetry on Top & Bottom


omega-fixedvalue at inlet & outlet (based on omega=k^3/2/kcmul) basically took from one journal paper.For wall omega wall function and value =60nu/betaXdely^2. Symmetry for Top & Bottom


nut-fixedvalue(0) at inlet, zerogradient at outlet,nutuspaladingwallfunction on wall, symmetry on Top and bottom.


Mesh details:
Y+=1, Four meshes are tested 50K,65K,80K,and 95K with max aspect ratio less than 22. The domain size is sufficiently long was used.


fvSchmes:
Time- Euler, gradschmes-Gauss linear, Divergence-Gauss limitedlinear,Laplacian-Gauss linear corrected
Interpolation-linear, Sngrad-corrected


Fvsolution:
PCG with DIC as preconditioner for pressure with tolerance of 1e-06, reltol=0
For other terms PBiCG with DILU ,tolerance 1e-08


Ncorrectors=2,northogonalcorrectors=3


Please help me to solve this problem friends, Hope I described all important details
aerosaravanan is offline   Reply With Quote

Old   September 26, 2014, 17:56
Default
  #2
Senior Member
 
Join Date: Nov 2010
Posts: 139
Rep Power: 16
taxalian is on a distinguished road
Send a message via Skype™ to taxalian
What about the time step size, did you try to use a smaller time step?
Quote:
Originally Posted by aerosaravanan View Post
Hi friends,
I am currently trying to simulate flow past a circular cylinder for my thesis in OpenFOAM. I am having problem in getting the correct strouhal number. Drag coefficient is comparatively good. The following are the BC’s and details about mesh
Dia=0.034 m; velocity=20 m/s; Re=45,000 ; Solver- PISOFOAM; RANS Model-kOmegaSST


P-freestreamPressure at inlet & outlet, zeroGradient on cylinder (wall), Symmetry on Top & Bottom


U-freeStreamVelocity at inlet & outlet, fixedValue (0) on wall, Symmetry on Top & Bottom


k-fixedValue at inlet (based on k=3/2(UI)^2),zerogradient at outlet, FixedValue (0) on wall and kqrwallfunction, Symmetry on Top & Bottom


omega-fixedvalue at inlet & outlet (based on omega=k^3/2/kcmul) basically took from one journal paper.For wall omega wall function and value =60nu/betaXdely^2. Symmetry for Top & Bottom


nut-fixedvalue(0) at inlet, zerogradient at outlet,nutuspaladingwallfunction on wall, symmetry on Top and bottom.


Mesh details:
Y+=1, Four meshes are tested 50K,65K,80K,and 95K with max aspect ratio less than 22. The domain size is sufficiently long was used.


fvSchmes:
Time- Euler, gradschmes-Gauss linear, Divergence-Gauss limitedlinear,Laplacian-Gauss linear corrected
Interpolation-linear, Sngrad-corrected


Fvsolution:
PCG with DIC as preconditioner for pressure with tolerance of 1e-06, reltol=0
For other terms PBiCG with DILU ,tolerance 1e-08


Ncorrectors=2,northogonalcorrectors=3


Please help me to solve this problem friends, Hope I described all important details
taxalian is offline   Reply With Quote

Old   September 27, 2014, 10:24
Default
  #3
New Member
 
Saravana Kumar Lakshmanan
Join Date: Feb 2013
Posts: 11
Rep Power: 13
aerosaravanan is on a distinguished road
Hi taxalian
Thanks for your interest. Intially I used 5e-06 which gave max courant number 0.6-0.8. After your post today, I simulated with the time step of 1e-06 such that the max courant number less than 0.2. I simulated more than 140 non dimensional time units to avoid transient effects and started to monitor the values of Cl and Cd.Still I am getting reasonable drag value but strouhal number is high.I calculated this through calculating the time interval between peaks of the Cl plot as well as FFT of the Cl values.Manual calculated value is 0.25 and FFT value is 0.2464.The actual value for Re 45000 is 0.20.I also attached my case.Please have a look.

https://drive.google.com/file/d/0B8S...it?usp=sharing
aerosaravanan is offline   Reply With Quote

Old   November 20, 2014, 17:48
Default
  #4
New Member
 
chubb87
Join Date: May 2011
Posts: 21
Rep Power: 15
chubb87 is on a distinguished road
Did you solve your problem?

I would recommend using pimpleFoam instead of pisoFoam, to make sure convergence is achieved with a convergence criterion. I made the experience that with pisoFoam no relaxation should be used, but it seems you do not use relaxation.

Isn't Y+=1 rather low, since you are using wallfunctions?
chubb87 is offline   Reply With Quote

Old   November 23, 2016, 09:45
Default
  #5
Member
 
subhankar
Join Date: May 2016
Posts: 36
Rep Power: 10
SUBHANKAR is on a distinguished road
Hi all,
I am solving a similar problem but with reynolds number =100. I got strouhal number same but am unable to get correct Cd(drag co-efficient).

drag co-efficient(Cd) calculated from the forceCoeff.dat through numerical integration doesn't match with that calculated from the formula
Cd=F(drag force)/(0.5*density*diameter*Umax^2) and neither of them confirm with the actual result. Can anyone explain why? Since i am using 2-d simulations so in place of area in the Cd formula i used the diameter of the cylinder over which my flow is taking place.
regards
Subhankar
SUBHANKAR is offline   Reply With Quote

Reply

Tags
cylinder, incompressible, komegasst, openfoam, shedding

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Which Foam for vortex shedding problem Madeleine P. Vincent OpenFOAM 7 November 20, 2018 07:31
fluent gets wrong airfoil vortex shedding frequency eaglexyb FLUENT 0 July 19, 2012 11:39
how can I determine the vortex shedding time step Zhe Liu CFX 3 July 30, 2008 18:16
Vortex shedding? rbel038 CFX 4 April 27, 2008 20:57
basic vortex shedding john Main CFD Forum 4 November 6, 2000 14:23


All times are GMT -4. The time now is 05:33.