Analysis of flow around cylinder (2D)

katiyon · September 30, 2010, 14:28

has anyone obtained valid hydrodynamic characteristics (Cd, Cl, St number) of a flow around circular cylinder in low Reynolds (10 -40 ) regimes by CFX? i have a 2D model and there are a lot of things that are influence on result. such as domain size and ... i cant find all

Josh · September 30, 2010, 15:17

Hi Kate -

I performed a CFD analysis on a cylinder back when I was new to CFD. Naturally, the results weren't great because there were many things I didn't consider.

Two of the most important factors to consider are grid resolution (i.e., the solution doesn't change with further refinement) and grid quality (i.e., grid factors separate from resolution that affect simulation convergence). Spalart (Young-Person's Guide..., 2001) had a beautiful example of a well-resolved, high-quality grid for a cylinder. It's built for a DES simulation, but it largely encompasses the same considerations:

Avoid the overlap regions, if possible. Notice how the orthogonality, aspect ratio, skew, and other parameters are very high in quality in both the cylinder's immediate region and wake region.

Other factors are considered here:
http://www.cfd-online.com/Wiki/Ansys...gence_criteria

At that Reynolds number, you will need a laminar, unsteady solution to capture shedding.

vmlxb6 · February 10, 2011, 17:07

I am trying to simulate a flow over a cylinder. Its a 1 way FSI (moving mesh problem). Your mesh is very neatly made. I need a mesh like that but finding it hard to make one. Can you tell me which software did you use to create this mesh ??? Any tutorials available ???

ghorrocks · February 10, 2011, 17:57

Josh included a reference in his post, that is where the mesh he showed came from.

Note the mesh is an overlaping grid. CFX does not support overlapping grids so this mesh would not be useable.

But there are hundreds of studies of flow over a cylinder in the literature using all sorts of different techniques. It is a standard benchmark simulation. Do a search of the literature and you should find lots of them.

Josh · February 10, 2011, 20:31

I agree with Glenn. Though CFX does not support an overlapping mesh, you can still create a nice O-grid in ICEM with downstream refinement.

Here is an ICEM tutorial for creating a C-grid around an airfoil. The techniques would be similar for a cylinder.

http://www.youtube.com/watch?v=tYrbScUH9RE

September 30, 2010, 14:28	Analysis of flow around cylinder (2D)	#1
katiyon New Member kate Join Date: Jul 2009 Location: iran Posts: 29 Rep Power: 17	has anyone obtained valid hydrodynamic characteristics (Cd, Cl, St number) of a flow around circular cylinder in low Reynolds (10 -40 ) regimes by CFX? i have a 2D model and there are a lot of things that are influence on result. such as domain size and ... i cant find all

February 10, 2011, 17:07	Hi Josh,	#3
vmlxb6 Senior Member Ugly Kid Joe Join Date: Aug 2010 Posts: 193 Rep Power: 16	I am trying to simulate a flow over a cylinder. Its a 1 way FSI (moving mesh problem). Your mesh is very neatly made. I need a mesh like that but finding it hard to make one. Can you tell me which software did you use to create this mesh ??? Any tutorials available ???

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September 30, 2010, 15:17		#2
Josh Senior Member Joshua Counsil Join Date: Jul 2009 Location: Halifax, Nova Scotia, Canada Posts: 366 Rep Power: 18	Hi Kate - I performed a CFD analysis on a cylinder back when I was new to CFD. Naturally, the results weren't great because there were many things I didn't consider. Two of the most important factors to consider are grid resolution (i.e., the solution doesn't change with further refinement) and grid quality (i.e., grid factors separate from resolution that affect simulation convergence). Spalart (Young-Person's Guide..., 2001) had a beautiful example of a well-resolved, high-quality grid for a cylinder. It's built for a DES simulation, but it largely encompasses the same considerations: Avoid the overlap regions, if possible. Notice how the orthogonality, aspect ratio, skew, and other parameters are very high in quality in both the cylinder's immediate region and wake region. Other factors are considered here: http://www.cfd-online.com/Wiki/Ansys...gence_criteria At that Reynolds number, you will need a laminar, unsteady solution to capture shedding.

February 10, 2011, 17:57		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,852 Rep Power: 144	Josh included a reference in his post, that is where the mesh he showed came from. Note the mesh is an overlaping grid. CFX does not support overlapping grids so this mesh would not be useable. But there are hundreds of studies of flow over a cylinder in the literature using all sorts of different techniques. It is a standard benchmark simulation. Do a search of the literature and you should find lots of them.

February 10, 2011, 20:31		#5
Josh Senior Member Joshua Counsil Join Date: Jul 2009 Location: Halifax, Nova Scotia, Canada Posts: 366 Rep Power: 18	I agree with Glenn. Though CFX does not support an overlapping mesh, you can still create a nice O-grid in ICEM with downstream refinement. Here is an ICEM tutorial for creating a C-grid around an airfoil. The techniques would be similar for a cylinder. http://www.youtube.com/watch?v=tYrbScUH9RE