initial condition effect on wing lift

linyx · June 5, 2013, 21:42

NO, it is stead-state, it just increasing the angle of attack 1 degree a time, and decreasing 1 degree a time, difference will present in the loop of hysteresis.

http://www.sciencedirect.com/science...45782501003826

Aeronautics El. K. · June 6, 2013, 06:31

Quote:

Originally Posted by linyx

NO, it is stead-state, it just increasing the angle of attack 1 degree a time, and decreasing 1 degree a time, difference will present in the loop of hysteresis.

http://www.sciencedirect.com/science...45782501003826

1. I read the paper but I don't really get its point. What they do, is just to use the previous solution as initial condition for the next angle. However, the airfoil is not in a continuous pitching/plunging motion. Rather, it's at a fixed angle and the solution is steady state. So, why hysteresis?
I tried to find Hoffman's paper (Effects of freestream turbulence in the performance characteristics of an airfoil) that it's in the references there but I couldn't so if anyone has it, pm me please...
I would refer you to these papers:
http://www.sciencedirect.com/science...76042197000122
http://adsabs.harvard.edu/abs/1994AIAAJ..32.2359E
(just to name a few, there are a lot more...)

2. I also refer you to post #15

linyx · June 6, 2013, 08:24

Well, I cannot find that paper either. I did my case as they did, the same thing happend, the loop is around 25-30 angles, so the aerodynamic around these angles needs to take care. Actually their paper is not steady state all the time, during decreasing angles, the stalled wings needs to solve it unsteady.

Stall delay would happen in low freestream turbulance, single/multi-element airfoils cases. In fact, experiment also shows the stall delay or hysteresis would happen as the angle of attack increases, one degree a time to measuer the forces. See "An Experimental Investigation on Aerodynamic Hysteresis of a Low-Reynolds Number Airfoil" (you can google it for full paper), so that the last paper's CFD predition shows the trend.

As you said about the pitching/plunging motion, I think it is not only happend in this unsteady motions.

Anyway, I am doing the indepence study, but the mesh is too large (several millions)for a fine meshes, more time are needed to converge.

linyx · June 9, 2013, 07:57

I strongly suggest you to read this, which is a hysteresis in the static aerodynamic by experiment

http://web.ebscohost.com/ehost/pdfvi...4&vid=2&hid=25

Aeronautics El. K. · June 9, 2013, 08:35

Strongly? hahaha alright doc. I will

June 9, 2013, 08:35		#25
Aeronautics El. K. Senior Member Lefteris Join Date: Oct 2011 Location: UK Posts: 337 Rep Power: 15	Strongly? hahaha alright doc. I will __________________ Lefteris

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June 5, 2013, 21:42		#21
linyx Member Linyx Join Date: Mar 2011 Posts: 31 Rep Power: 15	NO, it is stead-state, it just increasing the angle of attack 1 degree a time, and decreasing 1 degree a time, difference will present in the loop of hysteresis. http://www.sciencedirect.com/science...45782501003826

June 6, 2013, 08:24		#23
linyx Member Linyx Join Date: Mar 2011 Posts: 31 Rep Power: 15	Well, I cannot find that paper either. I did my case as they did, the same thing happend, the loop is around 25-30 angles, so the aerodynamic around these angles needs to take care. Actually their paper is not steady state all the time, during decreasing angles, the stalled wings needs to solve it unsteady. Stall delay would happen in low freestream turbulance, single/multi-element airfoils cases. In fact, experiment also shows the stall delay or hysteresis would happen as the angle of attack increases, one degree a time to measuer the forces. See "An Experimental Investigation on Aerodynamic Hysteresis of a Low-Reynolds Number Airfoil" (you can google it for full paper), so that the last paper's CFD predition shows the trend. As you said about the pitching/plunging motion, I think it is not only happend in this unsteady motions. Anyway, I am doing the indepence study, but the mesh is too large (several millions)for a fine meshes, more time are needed to converge.

June 9, 2013, 07:57		#24
linyx Member Linyx Join Date: Mar 2011 Posts: 31 Rep Power: 15	I strongly suggest you to read this, which is a hysteresis in the static aerodynamic by experiment http://web.ebscohost.com/ehost/pdfvi...4&vid=2&hid=25