# Cl, Cd, Reference Values in 2D?

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 October 12, 2011, 12:37 Cl, Cd, Reference Values in 2D? #1 New Member   Mark Join Date: Oct 2011 Posts: 2 Rep Power: 0 Hi there, I'm fairly new to fluent so bear with me. Let me explain my situation: I am doing a 2D simulation of airfoils (to be more specific NACA 4421 and NACA 23012) and I am confused with what the Cd and Cl are in terms of. Is the Cd and Cl displayed while the simulation is running in units of per meter? Also, what should my reference area be? My chord length is 2, however, there are alot of opinions that say that the reference area should be the chord length, others that say that it should be the chord length squared. If you could give any input, that would be great! Thanks, sniperees.

 October 20, 2011, 13:04 #2 Member   Kailash Join Date: May 2011 Location: London, UK Posts: 45 Rep Power: 7 Hi, Use the chord length as the ref length. Cl and Cd are non dimensional and it cannot not said to be per m. 2D flow simulation over an aerofoil is analogous to flow past a wing of infinite span. Also make sure that you set the reference pressure correctly. Cheers

 October 20, 2011, 18:04 #3 Senior Member   Mohammad Join Date: Feb 2010 Location: Shiraz, Iran Posts: 108 Rep Power: 8 hi, in 2d simulations dept=1,length=chord,area=chord and about cl,cd,cm reference pressure is not important but reference velocity and density should be checked. yours, mohammad

 October 21, 2011, 10:47 #4 New Member   Ali Jafarizade Join Date: May 2009 Posts: 22 Rep Power: 9 in such a problem for a 2d prblem and for cd and cl refreance values for velocity,density,area and viscosity should be checked!

 July 2, 2016, 03:09 about cd #5 New Member   RAJA PRATHAP Join Date: Jul 2016 Posts: 2 Rep Power: 0 iam getting negative values for cd when trying to simulate flow over 2d airfoil.pls explain how to sort out this issue

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