high AoA in xfoil
high AoA in xfoil
(OP)
Hi,
I want to use xfoil to get CL and CD data for all angles of attack, i.e. the full 360 degrees.
This is for a NACA 4412 profile, Re = 0.708*10^6.
Has anyone ever tried this?
I'm beginning to think it's impossible as I get bombarded by "non convergence" and "no stagnation point found" errors.
I want to use xfoil to get CL and CD data for all angles of attack, i.e. the full 360 degrees.
This is for a NACA 4412 profile, Re = 0.708*10^6.
Has anyone ever tried this?
I'm beginning to think it's impossible as I get bombarded by "non convergence" and "no stagnation point found" errors.





RE: high AoA in xfoil
is Re = 0.7E6 "low", as in "XFOIL: An Analysis and Design System for Low Reynolds Number Airfoils, Conference
on Low Reynolds Number Airfoil Aerodynamics" ? (ie are there limits in the program ?)
RE: high AoA in xfoil
From what I remember of my advanced aero course, I'd doubt it. The algorithms for the different regions are likely quite different.
KENAT,
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RE: high AoA in xfoil
X-Foil documentation:
"XFOIL doesn't crash very easily, but it can happen.
A common cause is accidental specification of a silly flow condition, e.g.
ALFA 90
In viscous mode this will produce all sorts of numerical fireworks,
and possibly an arithmetic fault."
Don't be surprised if it won't work for alpha 90.
Dan
RE: high AoA in xfoil
RE: high AoA in xfoil
Suppose I'll just have to use the Viterna post-stall model, although I've never seen it used on a non-symetrical aerofoil. It can't be too dificult surely.
It's for a vertical axis wind turbine simulation.
RE: high AoA in xfoil
RE: high AoA in xfoil
RE: high AoA in xfoil
RE: high AoA in xfoil
Just realised that Ive never seen the the viterna corrigan model used to predict CM. Could I predict CM somehow by making a pitching moment from lift and drag?
RE: high AoA in xfoil
Let the airfoils that are stalled be represented by flat plate? At alpha 90 or more one can argue they're not airfoils anymore, aerodynamically speaking.
RE: high AoA in xfoil
These limits of the codes are well known,and in fact it has been used succesfully for laminar airfoil analysis but not for flow condition were only the solution of Navier/Stokes equation coupled with a turbulence model, can give physically acceptable results.
The argument of post stall behaviour is well treated in the publications of NREL, where this problem is studied in detail,since it's an important issue in wind turbine blades behaviour.
Have a look there, you will find also a code to obtain the cl/cd curve for a profile working on a rotating blade.
RE: high AoA in xfoil
However, if you were using a NACA 4412, which has a zero-lift angle of attack of about -4 degrees, would you shift the viterna model by 4 degrees to the left?
For some reason I can't get access to the original Viterna-Corrigan paper from NREL. Strange because most of their stuff is publically available in mt previous experience
RE: high AoA in xfoil