Drag coefficient not even close

MDCLXXXVII · February 20, 2011, 07:38

I am a mechanical engineering student on mye 2nd year and therefore have no prerequisites on doing CFD (taking first fluid course now). However I participate in Formula student, and we hope to use CCM+ a lot.

I started doing the tutorial on this site: http://www.computationalfluids.com/library.htm (flow around circular cylinder)

The problem is I can not get the right value for the drag coefficient. As seen in the picture below, the value -0,0866... is way to low, as it should have been 0,4 and separation at 120degrees. Is this the right way to measure the drag coefficient?

The mesh is 13566 cells (the largest one in the tutorial)
Re: 15,7x10^6
water at 10m/s
cylinder D=1,4m

Ladnam · February 23, 2011, 16:17

You don't need segregated fluid temperature and I think you need a better mesh to get close to the experimentally obtained value. Try trimmer mesh with prism layers.

MDCLXXXVII · March 4, 2011, 04:24

But is the drag coefficient actually that far away?

I have read that Cd is dependant on Re, turbulence, wake and that the high Cd of 0,4 do belong to the laminar regime.

At this setup, water is entering at 10m/s. Maybe 0,0866 is not that far away?

February 20, 2011, 07:38	Drag coefficient not even close	#1
MDCLXXXVII New Member Join Date: Feb 2011 Location: Norway Posts: 2 Rep Power: 0	I am a mechanical engineering student on mye 2nd year and therefore have no prerequisites on doing CFD (taking first fluid course now). However I participate in Formula student, and we hope to use CCM+ a lot. I started doing the tutorial on this site: http://www.computationalfluids.com/library.htm (flow around circular cylinder) The problem is I can not get the right value for the drag coefficient. As seen in the picture below, the value -0,0866... is way to low, as it should have been 0,4 and separation at 120degrees. Is this the right way to measure the drag coefficient? The mesh is 13566 cells (the largest one in the tutorial) Re: 15,7x10^6 water at 10m/s cylinder D=1,4m

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February 23, 2011, 16:17		#2
Ladnam Member Join Date: May 2010 Posts: 40 Rep Power: 15	You don't need segregated fluid temperature and I think you need a better mesh to get close to the experimentally obtained value. Try trimmer mesh with prism layers.

March 4, 2011, 04:24		#3
MDCLXXXVII New Member Join Date: Feb 2011 Location: Norway Posts: 2 Rep Power: 0	But is the drag coefficient actually that far away? I have read that Cd is dependant on Re, turbulence, wake and that the high Cd of 0,4 do belong to the laminar regime. At this setup, water is entering at 10m/s. Maybe 0,0866 is not that far away?