- #1

Graviman

- 19

- 0

Kind aerospace folk,

Preamble:

I'm trying to write my own aerofoil vortex panel method, but have run into some difficulties. The method is designed to work in Excel, so is limited in matrix size for reliable inversion (for vortex / velocity matrix). This means that the traditional method of a large number of panels in unrealistic. The original aerofoil data is limited to 11 points each for top and bottom surfaces and leading and trailing edge radii.

Having read Abbott & Doenhoff, I have decided to try to update the original 1940s aerofoil analysis methods. This means that i define both top and bottom surface geometries each as a polynomial, with a maximum of 10 terms. To me it seemed logical that the surface vortex distribution would also be a polynomial of similar order, with separate equations for top and bottom surfaces.

So far the method looks promising, with the surface normal velocities all meeting the no through flow boundary condition. But, i have run into difficulties with the tangential velocity distribution. Specifically how to implement the Kutta condition for no trailing edge circulation (at low AOA). Having read various papers i decided that although equal and opposite trailing edge vortices are often quoted, what is really required are equal top & bottom surface trailing edge tangential velocities. This then begs the question of how do i achieve the correct trailing edge outflow velocities (relative to free field velocity), and ensure the correct overall tangential velocity distribution.

The question(s):

Has anyone here had a go at writing their own vortex panel method?

Do any of the difficulties described here sound familiar?

Are there any techniques not documented in the literature that i am overlooking?

My plan is to compare the results i get with this code:

http://www.engapplets.vt.edu/fluids/vpm/index.html

The final step will be validation by CFD, and then some physical testing (maybe).

Thanks in advance,

Mart

Preamble:

I'm trying to write my own aerofoil vortex panel method, but have run into some difficulties. The method is designed to work in Excel, so is limited in matrix size for reliable inversion (for vortex / velocity matrix). This means that the traditional method of a large number of panels in unrealistic. The original aerofoil data is limited to 11 points each for top and bottom surfaces and leading and trailing edge radii.

Having read Abbott & Doenhoff, I have decided to try to update the original 1940s aerofoil analysis methods. This means that i define both top and bottom surface geometries each as a polynomial, with a maximum of 10 terms. To me it seemed logical that the surface vortex distribution would also be a polynomial of similar order, with separate equations for top and bottom surfaces.

So far the method looks promising, with the surface normal velocities all meeting the no through flow boundary condition. But, i have run into difficulties with the tangential velocity distribution. Specifically how to implement the Kutta condition for no trailing edge circulation (at low AOA). Having read various papers i decided that although equal and opposite trailing edge vortices are often quoted, what is really required are equal top & bottom surface trailing edge tangential velocities. This then begs the question of how do i achieve the correct trailing edge outflow velocities (relative to free field velocity), and ensure the correct overall tangential velocity distribution.

The question(s):

Has anyone here had a go at writing their own vortex panel method?

Do any of the difficulties described here sound familiar?

Are there any techniques not documented in the literature that i am overlooking?

My plan is to compare the results i get with this code:

http://www.engapplets.vt.edu/fluids/vpm/index.html

The final step will be validation by CFD, and then some physical testing (maybe).

Thanks in advance,

Mart

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