Comparison of LLT and VLM method

[Parul]

Hi
1. I am doing XFLR analysis for a rectangular wing with high AR, I am getting differnt values of CL and CD for differnt methods i.e. LLT and Horseshoe Vortex(VLM1). Can you please explain the reason and which one is accurate? Also, why LLT method is not available in Stability Analysis?
2. In VLM analysis, why CL doesn't vary with velocity and density?

LLT Method:

Vel	alpha	CL	CD
10	7	1.305	0.060
15	7	1.386	0.056

Horseshoe Vortex Method (VLM1)

Vel	alpha	CL	CD
10	6	1.586	0.078
15	6	1.586	0.069

LLT & VLM1

Vel	alpha	CL	CD
15	7	1.683	0.111
15	7	1.386	0.056

Thanks
Parul

[André]

1. No method is accurate
2. Panel methods are based on the Euler equations which are invisicid, and therefore results do not depend on velocity.

[Parul]

If one is to be chosen out of them which one shall I use for low subsonic incompressible flow?
Thanks

[Rohan]

This is a good question. LLT should be more accurate, Andre' to confirm....

[Marko J.]

Anf if your wing has a AR of 6 or higher and your sweep angle is 0 or has a very small angle. The LLT is the best method for you. LLT is also nonlinear.
The other Methods VLM and Panel are only linear but give you sufficent accurate results when you have small AR and/or large sweep angle.
In the guidlines of XFLR5 you could read a more detailed description

[Chantell Black]

Hi,

André you say that:
Panel methods are based on the Euler equations which are invisicid, and therefore results do not depend on velocity.

Apparently Euler equations are compressible? Is that correct? And if so, I thought XFLR5 does not account for compressibility? So how does panel methods use Euler? Sorry for all the questions.

Kind Regards,

Chantell