# lift & drag coefficient on airfoil

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 August 29, 2005, 05:39 lift & drag coefficient on airfoil #1 n. natik Guest   Posts: n/a dear sirs how can i calculate the lift & drag coefficient on airfoil surface for 2-d incompressible case, for fluent post processing i can calculate and draw only cp(pressure coefficient), what about lift & drag coefficient ?? thanks in advance for your early replay

 August 29, 2005, 06:26 Re: lift & drag coefficient on airfoil #2 Jason Guest   Posts: n/a You can monitor lift & drag coefficients while your solution iterates by going to Solve->Monitors->Forces. In fact, if in your final results you want the lift & drag coefficient, then you should monitor them to ensure convergence. Once you have a final solution you can get forces and moments from Report->Forces. It will print the force (or moment) in your units and in coefficient terms. Make sure you've defined your reference values at Report->Reference values. A sticking point is that "length" is the reference length used in the moment coefficient (Cm = 1/2*Rho*V^2*Aref*Lref) while "depth" is the length of your model in the z direction. If you set "depth" to 1, then it's a per unit length setup. Hope this helps, and good luck, Jason

 October 23, 2009, 01:59 dear sir.. #3 New Member   vivit Join Date: Oct 2009 Posts: 2 Rep Power: 0 Can you tell me?? What is the Basic Calculation of FLUENT on Computing Lift Coef In Modelling 2D?? thanks

 October 23, 2009, 18:38 #4 Senior Member     teguh hady Join Date: Aug 2009 Location: Saga, Japan Posts: 222 Rep Power: 17 Hy vivit apriliyanti!! My problem is same as yours!! I think that 2d airfoil don't have A!!! So if A equal to 0 then Cl will be infinite!!! But when we run FLUNT 2D we'll see VOLUME after check our grid!!! the value of volume is not zero!! I think the value of Cl is based on that volume!! hope it helps!! teguhtf

 December 7, 2009, 06:25 hello mister #5 New Member   vivit Join Date: Oct 2009 Posts: 2 Rep Power: 0 wahat is grid independensi in FLUENT? please you explain,thnks

 December 16, 2009, 07:22 Basic Computation Of 2D #6 Senior Member     teguh hady Join Date: Aug 2009 Location: Saga, Japan Posts: 222 Rep Power: 17 Sorry, for waiting. After searching in some books, I've opinion that For solving Cl & Cd in 2D. There is assumption that the value of A is 1. you can read this on Anderson Computational Fluid Mechanics And Heat Transfer. Hope it helps teguhtf __________________ Now Or Never!!!

December 16, 2009, 10:14
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JT.Q
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Quote:
 Originally Posted by n. natik ;123784 dear sirs how can i calculate the lift & drag coefficient on airfoil surface for 2-d incompressible case, for fluent post processing i can calculate and draw only cp(pressure coefficient), what about lift & drag coefficient ?? thanks in advance for your early replay
1、for a 2d case,take x-y plan for example, the length in z direction is 1, so A=L(m)*1=L(m)
2、in force report panal, you can set the force vector to obtain cd and cl respectively.set x=1 and y=0,you will get cd,if x is the velocity direction.set y=1 and x=0, you will get cl.

December 17, 2009, 08:30
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 Originally Posted by vivit apriliyanti wahat is grid independensi in FLUENT? please you explain,thnks
Grid independence means that your solution does not change appreciately when you refine your mesh.

March 31, 2015, 19:02
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Quote:
 Originally Posted by Jason ;123785 You can monitor lift & drag coefficients while your solution iterates by going to Solve->Monitors->Forces. In fact, if in your final results you want the lift & drag coefficient, then you should monitor them to ensure convergence. Once you have a final solution you can get forces and moments from Report->Forces. It will print the force (or moment) in your units and in coefficient terms. Make sure you've defined your reference values at Report->Reference values. A sticking point is that "length" is the reference length used in the moment coefficient (Cm = 1/2*Rho*V^2*Aref*Lref) while "depth" is the length of your model in the z direction. If you set "depth" to 1, then it's a per unit length setup. Hope this helps, and good luck, Jason
Hello

I am simulating the flow over a 2 element airfoil which is to say that there is a main wing and a flap. I want all coefficients to be scaled to a unit chord. I am unsure whether FLUENT uses the real length of the airfoil or the reference length. I calculate both the lift and drag coefficient on the main, flap and both. However only the main wing and flap combined chord is 1m.

I am not quite clear from your explanation what whether FLUENT is assuming a unit chord for all calculations of CL and CD regardless of actual size or if it assumes the actual size. Depth is the z direction or the span of the wing and the length is used for moment how do I define a unit chord? is it in the area value?

Thanks in advance for the help.

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