[gub007]

I am trying to determine the drag coefficient of a circular cylinder diameter 0.03m at Re = 10^5 as a test case before using my mesh etc to investigate the drag and lift of a pentagonal cylinder. For some reason, I am getting a Cd of 0.43 which is much lower than the literature value of 1.2 and I cannot work out why. I am using a RANS k-omega SST solver with a localised mesh which keeps the y+ value between 30-50. Any advice would be much appreciated.

[LuckyTran]

The most common mistake is people have no idea what a Cd is or how it should be calculated. So...

How do you calculate the Cd? Show all your work. I clicked some reports is akin to I looked it up in the answers section in the back of the book. Can you reproduce the 0.43 if you calculate it by hand?

[gub007]

Hi LuckyTran,

Thanks for your response. I know how to calculate Cd using Cd = Fd / ((L*D) * U^2 * p * 1/2) and have inputted my reference values correctly so this is not the issue.

[LuckyTran]

And this is from a 2D case? 3D case? Again, show your work. Or be content with not getting any help because help is not what you want.

[gub007]

This is for 2D simulation - what do you mean by show working?

[SanSiEzE]

The 2D problem always had the wrong result for "Force" because in ANSYS Fluent, the default thickness for a 2D case is 1m. Besides, a big yplus value would cause a wrong velocity near the wall, so you might want to check if the velocity near the wall is correct. If the velocity is wrong, the wall shear stress will be wrong too.

[Isha_T]

Hey, what value did you put for D and L?