## Curvature of airfoils

## Curvature of airfoils

(OP)

Hi,

Does anyone know whether there exists a standard way, or any other method, to smoothen the curvature of airfoils without changing the geometry too much?

Thanks in advance,

Gerrit

Does anyone know whether there exists a standard way, or any other method, to smoothen the curvature of airfoils without changing the geometry too much?

Thanks in advance,

Gerrit

## RE: Curvature of airfoils

## RE: Curvature of airfoils

I want to slightly change the nodes, especially with respect to eachother, to smooth the curvature, without really changing the geometry too much.

...but not by hand, so I'm looking for a method...

## RE: Curvature of airfoils

Have you double checked the source data and your transposition of it?

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## RE: Curvature of airfoils

(The source data is whimsical, that's why)

## RE: Curvature of airfoils

## RE: Curvature of airfoils

The point is that continuity in the second derivative doesn't assure smoothness in the curvature at all, it just assures you continuity (and I wonder whether continuity in the 3rd derivative will... so, some kind of filter or smoother has to be applied).

## RE: Curvature of airfoils

## RE: Curvature of airfoils

## RE: Curvature of airfoils

## RE: Curvature of airfoils

if you know the airfoil section you wanted, like from NACA data, it'd be alot easier ... but then you wouldn't be fussing with this stuff ...

## RE: Curvature of airfoils

## RE: Curvature of airfoils

Exactly how rubbish are the points you have? Do you have a high density of noisy points, or just a few points that need to be joined up gracefully?

Cheers

Greg Locock

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## RE: Curvature of airfoils

I'll have a look at octave, anyway I use to use fortran to to this stuff.

And yes, I could do curve fitting, using whatever kind of tool, but I'm looking for a reasonable objective criterion to do local fitting automatically by some fortran code.

Even though the density of the nodes I happen to have now is rather low, I'd prefer a day of coding in stead of starting up some curve tool (having to learn it) and doing the process by hand.

That is why I asked for a method. With a method I meant a mathematical criterion to exclude or deviate or include points in your local fitting scheme to be able to automate the task. To do so, you need to filter the whimsical curvature data and use that as a goal within a maximum allowed deviation from the original geometry.

Obviously, if you do it by hand, and you pull some Beziers, it's straightforward indeed and a natural fit with Beziers is an option, but I'm not looking for that option.

Anyway, I'll look at octave, because I've heard more positive things about it.

Thanks,

Gerrit

## RE: Curvature of airfoils

If the latter than you may need to change approach as you work around the perimeter.

Cheers

Greg Locock

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## RE: Curvature of airfoils

1. Far better computational convergence at los Reynoldsnumbers in programs like Xfoil.

2. Easier to convert it into a CAD surface automatically.

When you talk about noisy data, you probably refer to measurements from an already manufactured surface, that's not the case.

Gerrit

## RE: Curvature of airfoils

## RE: Curvature of airfoils

Ultimately it's NURBS, the mathmatical basis for all "Computer Graphics" today.

## RE: Curvature of airfoils

google for Xfoil or Profili2, IIRC Xfoil can do smoothing of airfoil coordinates.

Michael

## RE: Curvature of airfoils

Thanks for all your answers.

@rb1957:

No, I didn't mislead you. I don't want to interpolate between sparse data, I'd like to change the curvature of a discretised airfoil, slightly moving the same nodes. I think this can be done in a discretised way, without any curve fit.

@sreid

Nurbs is about the worst choice for aerodynamic surfaces, the curvature of any automatically generatied nurbs are like the rocky mountains, even if they look nice smooth and shiny at first. A good surface is defined by single bezier surfaces.

@mihumihu

What are these programs about? I found profili, but not IIRC

Gerrit

## RE: Curvature of airfoils

it sounds as though you are using synthetically generated profiles, in which case that is not the problem.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

## RE: Curvature of airfoils

IIRC = If I Recall Correctly. Not a software program, just a common shorthand.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.