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-   -   von karman issue (http://www.cfd-online.com/Forums/fluent/43132-von-karman-issue.html)

 Rafal Zamorowski December 14, 2006 16:54

von karman issue

I am trying to simulate von karman street over square cylinder. I am trying diffrent models of k=e with enhanced wall treatment. y+ of wall is less then 1. dimension of vortex generator (square cylinder)is 1 cm. Width of channel is 10 cm lenght is 30 cm (2D). from strouhal number formula time step is 0.0004 for velocity 5m/s. fluid is water. Boundary is velo inlet, on side walls of channel is symetry , outflow. Intensity of turb in initial boundary condition is 10 percent, lenght scale of vortex is 0,1m. All i got from this calculations is straight (like higway) wake behind cylider without any detaching vortices. I tried also to force fluent to detach vortices (to shear or cut the wake) by patching (perpedicular to mean flow) velocity behind cylider. I ve been working with this for loooong time (with different velo, and meshes, also with circular cylinder)but i cannot find what is wrong

 khairy January 1, 2007 14:45

Re: von karman issue

Hi,

1- use dimensionless time 0.005 in your case try dt =1e-6 seconds 2- use unsteady solver 3- u may need increase the side distance to 15 cm 4- are u scale this grid in gambit 5- use tri grid without patching or patch with structured grid ,as the non symmetry in triangle grid cause the required patching 6- use low re k-e for y+ <1

i hope this useful Khairy -Egypt

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