Vorlax vs Cart3D

[B-ROB]

Although VSP does not contain or support Vorlax anymore, it still is used by people using version 1.9 or before.

 

Has anyone compared the accuracy of Vorlax vs Cart3D?  How much better is Cart3D, and in what regimes?

[Rob McDonald]

I don't know of any published comparisons of Vorlax and Cart3D.
However, you should be able to find references which evaluate each
separately.

Vorlax is a vortex lattice code. My experience with Vorlax is that it
gives results far better than you have any right to expect. However,
it is a linearized potential flow code and is subject to all of the
limitations that come with that set of simplifications. It is pretty
good at what it can do - and worthless for everything else.

Cart3D is an Euler code. My experience with Cart3D is that it is
extremely productive when used with the adjoint based mesh adaptation
capability. It is very good at what it can do - and it can do a lot
more than a vortex lattice code.

Do you have a specific application in mind?

Rob

[B-ROB]

Hi Rob,

Two applications:

1. Determining subsonic aerodynamic characteristics of an aircraft in cruise condition.

2. Determining stability and control derivatives for said aircraft.

[Rob McDonald]

'Subsonic aerodynamic characteristics' can mean a lot of things.

Assuming your aircraft is solidly subsonic (not transonic), then
Vorlax or another vortex lattice code (AVL, VLAERO, etc) is probably
adequate for your use.

A Vortex lattice code will do a decent job of modeling:
Lift, linear lift curve, zero lift angle of attack, lift curve slope,
lift distribution, major aerodynamic loads, induced drag, pitching
moment, control surface effects, control derivatives, etc.

A Vortex lattice code will not adequately model:
Wave drag, transonic drag rise, transonic nonlinear effects, viscous
effects - stall, skin friction drag, form drag, etc.

Hope this helps,

Rob

On Mon, May 28, 2012 at 11:19 PM, B-ROB <brenta...@yahoo.com> wrote:

[B-ROB]

Thanks, Rob.  I appreciate your replies.

[Nathan Van Ymeren]

Hi Rob,

Have you used either AVL or VLAERO? Would you recommend one over the other as a replacement for those of us who can't get/don't have Vorlax?

N

[Mark Moore]

I would personally recommend XFLR5, which is freely available on the internet.  In several ways it is better than Vorlax in that the 2D viscous induced drag is calculated because it builds up the 3D analysis from 2D XFOIL analysis.  So all the specific 2D airfoil data is captured, in a better way than Vorlax's flat plate method (that doesn't include the 2D effects).

I would  love to be able to go straight from VSP to XFLR5, but haven't looked  into doing that.  Putting in an XFLR5 model is very easy - but it would be nice to do a  direct export from VSP. 

We  have  used this for our UAS studies and  have gotten very good results.  Even thought XFLR5 says to be careful not to use for full size aircraft (as mostly this tool is used for small UAV sized aircraft).  Everything is valid for larger aircraft.

But I would be interested in hearing other peoples opinion about this.

Mark

[Rob McDonald]

My students have used AVL, I have no personal experience with AVL or
VLAero. There are plenty of other vortex lattice codes out there as
well.

Mark mentioned XFLR5. It is an open-source mashup of XFoil and AVL.
It does not have the academic pedigree of pure AVL, but it does have
an enthusiastic community of users who work hard on it.

I have spoken with industry users who have gone with VLAero because
they get high quality support from the company. It isn't free, but
having a phone number to call for help has a lot of value.

None of these tools have a strong record of published
validation/verification articles. You're left to trust that the
developers have performed lots of tests along the way. No matter
what, you'll want to do some tests of your own to make sure you're
getting the kind of results you need.

Rob

[Nathan Van Ymeren]

Thanks Rob and Mark, I appreciate the insight.