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June 10, 2012, 00:57 
Solver for the lift coefficient

#1 
New Member

Hello everyone,
I have this basic question kept striking my mind that whether we can predict the coefficient of lift of a cambered airfoil (symmetric/non tapered) without first actually getting it tested in a wind tunnel? If so, anyone please help me with the most basic doubt of mine and help me find a solver that best suits it. ( I basically look forward to FLUENT AND CFX). I am a total novice in this field and desperate to know it. Thanks to everyone. 

June 15, 2012, 18:58 

#2  
New Member
Ricardo
Join Date: May 2012
Posts: 8
Rep Power: 6 
Quote:
Try to get Xfoil software. You can download it from http://web.mit.edu/drela/Public/web/xfoil/ You can simulate modified profiles getting the new Cl and Cd curves. For this simply case, its not necessary fluent or CFX. Ricardo 

June 19, 2012, 13:01 

#3 
New Member

Thanks a lot Ricardo for giving your time to write me.
But does that mean that I should convince myself that there is a possibility to get the lift coefficient through FLUENT or CFX? Thanking You 

June 26, 2012, 07:56 

#4 
Senior Member

What is the range of reynolds numbers and type of airfoils you are going to test?
If your airfoil is more or less standard and flow is subsonic, it is better to use xfoil, since you will get much less accurate result with RANS modelling of turbulence in FLUENT or similar CFD software. Flow separation with laminarturbulent transition at low Re numbers is a very weak point of software that uses RANS models. Truffaldino 

June 26, 2012, 12:14 

#5 
New Member

Thank you truffaldino
My reynolds number is definitely not to exceed laminar constraints and flow is subsonic. But you gave me an excellent idea about the two software I was confused with. When I switched to the above link [as stated by ricardo.costa], I found link to many other softwares like xfoil, Javafoil, Designfoil, XLR5 as well. So I wonder, what models do they use to get all those readings. And moreover if the data of each and every airfoil is predefined in the program then how can they have such low size in the disk.? Thanking you sumit_raised 

June 26, 2012, 12:16 

#6 
New Member

Thank you truffaldino
My reynolds number is definitely not to exceed laminar constraints and flow is subsonic. But you gave me an excellent idea about the two software I was confused with. When I switched to the above link [as stated by ricardo.costa], I found link to many other softwares like xfoil, Javafoil, Designfoil, XLR5 as well. So I wonder, what models do they use to get all those readings. And moreover if the data of each and every airfoil is predefined in the program then how can they have such low size in the disk.? Thanking you sumit_raised 

June 26, 2012, 14:50 

#7 
Senior Member

Hello Sumit_raise,
Not of all software you found is quite good. I do not advice to use Javafoil as it uses a quite primitive boundary layer method and could be very innacurate. XFLR5 and Xfoil are essentially the same: XFLR5 uses Xfoil for each 2D section to get a polar of the whole wing/aircraft. Xfoil is indeed of a very small size and very fast: basically you could spent weeks of runtime doing Large Eddy Simulation with CFDsotware like FLUENT, while Xfoil will give you a result with the same accuracy just in a fraction of second. Since Xfoil is based on different principles and does not solve directly NavierStokes equation directly on big meshes, it is faster and much more smaller, but it only works for flows with moderate separation regions, where viscousinviscid bl interaction approximation is valid. To locate laminarturbulent transition it uses some tabulated data from orrsommerfeld theory in cojunction with empirical e^n method. This software gives a quite accurate results for more or less conventional airfoils, but it is not applicable to a flow past cylinders, squares, stepped airfoils and other exotic stuff. Truffaldino 

April 11, 2013, 04:50 

#9  
New Member
M. Abdul Akbar
Join Date: Feb 2013
Posts: 19
Rep Power: 5 
Quote:
Is Xfoil a good software for obtaining lift and drag coefficients of aerofoils that are in low Reynolds number regime (typical of vertical axis wind turbines) ??. Thanks 

April 11, 2013, 11:20 

#10  
Senior Member

Quote:
As for other softwares: I have tried RANS with Fluent and it is much less accurate, LES with fluent takes an enormous time and seeems to be also less accurate than Xfoil 

January 21, 2014, 05:00 

#11 
New Member
M. Abdul Akbar
Join Date: Feb 2013
Posts: 19
Rep Power: 5 
Hi truffaldino,
Thanks. This reply might be coming after 9 months but nevertheless, it is on course because ever since your last response, I have downloaded XFLR5 and have started playing around with it. The following are the three methods to find lift and drag coefficients by RANS method using OpenFOAM by LES method using FLUENT by Vortex lattice method using XFLR5 My questions are the following: 1) Are there any other methods to find the lift and drag coefficient other than those three mentioned above 2) For LES method, is there any Open source free software which is equivalent to FLUENT Looking forward to your response. Thanks in advance Regards, Abdul Akbar 

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