# no karman vortex street occur in the simulation of the flow over a cylinder

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November 8, 2021, 04:49
no karman vortex street occur in the simulation of the flow over a cylinder
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Hello,
I have trouble making a simulation of the flow over a circle cylinder.
Fig.1 is the 2D case I did before, and Karman vortex street appeared obviously.

But when I try to do a 3D case, the wake becomes straight and no periodic vortex shedding (Fig.2-Fig.5)

Parameters of the case:
·Diameter=0.01m
·Height=0.03m
·Velocity of the incoming flow=0.01m/s
·Reynolds number=100 (laminar flow)

The fluid region:
·X Direction(incoming flow): -7.5D/+25D from the axis of the cylinder
·Y Direction: ±10D from the axis
·Z Direction: 1D from the top/bottom face of the cylinder

Boundaries:
·Faces of the cylinder: walls
·Inlet/ outlet: velocity inlet/ pressure outlet
·Top & bottom faces(along the Z axis): symmetry
·Side faces(along the Y axis): walls

Physics:
·3D
·Segregated Flow
·Laminar
·Constant Density
·liquid(water, μ=1.002e-3Pa·s, ρ=998kg/m³

I have refined the mesh from 800 thousand to 5 million, so it is unlikely to be a problem of grid.
In fact, I had also try to simulate the turbulance case using k-ε and k-omega SST(u=0.394m/s, Re=3900), but the flow field looks similar to the laminar one (Fig.2-Fig.5)
Attached Images
 2d.png (62.0 KB, 18 views) 10s.jpg (197.6 KB, 21 views) 20s.jpg (196.9 KB, 15 views) 30s.jpg (193.1 KB, 14 views) 40s.jpg (187.4 KB, 12 views)