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Trying to find resistance of a submerged body using 2D simulation

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Old   October 15, 2017, 03:47
Exclamation Trying to find resistance of a submerged body using 2D simulation
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Rishabh Kumar
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So I have this Problem, I have an axisymmetrical body on which I have to perform simulation to find out Drag coefficient and overall resistance at certain flow speed.

Uisng Star CCM+, I made the sketch of the flow domain in XY plane and extruded it to 0.1m in Z direction and followed the steps required to get the solution.

Now, the drag force which I'm getting, is it the drag force of a whole body area or just the strip of extruded distance ?

I'm confused so much any help will be appreciated : )
I'm attaching my sketch and my mesh screenshot to explain what I'm talking.

my model has a surface area of 17.2m2 and I'm getting a resistance of 310N
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Old   October 16, 2017, 09:30
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The help documentation is not really clear on this subject. I believe that a Cartesian 2D mesh results in forces per unit length which would mean that you are probably getting forces per radian from an axisymmetric analysis. I would contact support and ask them to clarify. I know I have run into issues with their force calculations before that resulted in some internal debate on their end on how it should be done.

The alternative would be to do some kind of reality check. Do you have some idea of the order of magnitude you should see on the drag? If it is an order of magnitude lower than what you think it should be then you probably need to multiply by 2*pi (i.e. integrate f*dtheta).

If you really want to be confident, I would extract your pressure and shear distributions and integrate them yourself.
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Old   October 16, 2017, 14:39
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Hi! Thanks so much for replying so quick! I was also thinking of doing the same check, for this I did the CFD analysis of a 3D body to find the same forces. What I found is that they were closer to (2*pi) times the forces calculated previously in axisymmetric analysis.

But to be sure, I'll be doing it for different flow speeds and comparing it again. I'll post the results here if needed : )
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Old   October 19, 2017, 04:31
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Soroush Kargar
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The best way possible to get a 2D simulation is that you build up your sketch in CAD design of STAR-CCM and extrude it whatever you want. But the side you want to study the problem must be on XY plane with z=0.
Then you should convert it into a 2D mesh using the option Mesh>Convert to 2D.
This requires that you delete any 3D domain,mesh and region (if u had built any before).
Then your problem is fully converted into a 2D realm so there won't be confusions about defining the faces to report the results upon since you have to deal with edges instead of faces now.

Hope it works
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resistance, resistance force, star ccm+ help, submerged body

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