Best way to model fowler flaps?

[Jeremy S]

What's the best approach to model a fowler flap that translates aft .3*chord?

Is there already a feature that does this that I'm not finding?

Or for that section of the wing with fowler flaps should I model the wing section 30% longer? In which case I'd need two separate models to analyze with and without flap deflection. But the longer chord length would also increase the airfoil thickness for that section, which isn't exactly accurate either. 

Thoughts?

Not looking to find CLmax or stall AoA, interested in predicting the changes to pitching moment, downwash angle, predicting stability derivatives. Goal is to compare VLM results to MATLAB script I've wrote.

Thanks,

Jeremy

[Rob McDonald]

Erik Olson has a paper on this that you should look for.

In the simplest approach, I would copy/paste your main wing segment.  Then change the airfoil to your flap airfoil.  Then use the 'Modify' tab to translate / rotate / scale the flap element into position (relative to the main element).

This way, you can still use the main wing planform parameters to match -- aspect ratio, span, sweep, etc.

Rob

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[Brad Walker]

Hey Rob,

I'm an amateur airplane builder and lurk on this list.

Would you be so kind as to post a reference to the paper by Erik Olson. I would be really interested in this..

Thanks.

-brad w.

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[Rob McDonald]

He gave a presentation at the 2019 Workshop...

http://openvsp.org/wiki/lib/exe/fetch.php?media=workshop19:openvsp_workshop_190917_high_lift.pdf

And there was this paper

https://arc.aiaa.org/doi/10.2514/6.2016-1274

Which is available from NTRS

https://ntrs.nasa.gov/citations/20170006246

Rob

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[Rob McDonald]

Miro,

FYI.  The supplied image is from a CompGeom mesh, not a CFDMesh.

Rob

On Mon, Jan 3, 2022 at 12:51 PM Miroslav Grulovic <miro_g...@yahoo.com> wrote:

Hello Erik, happy new year.

I have tried to understand your method of creating flaps while waiting for more comprehensive and elegant way for modeling control surfaces ( ailerons, rudder etc.. )

I am in little project which uses PMARC14, and while experimenting with PMARC14 geometry modeling I came across one of  your article with picture depicted below.

 I have found and downloaded your model from HANGAR  ( File # 415 ) since picture looks like VSP output in CFD stl format as half mesh, I tried  to replicate.

Unfortunately  VSP ( 3.25 & 3.26 ) crashed while executing.

From your published papers  I have concluded that your piece of software HOrDE was used at some point but I could not figure where and how.

 Some times ago I have with NASA permission obtained a copy oh HOrDE but even with your assistance I was not able to even launch it.

Now, at this point of time I am interested only to steps needed to create CFD stl file of half mesh of EET AR=12 ( your model # 415) obviously there is something that I could not figure out all by myself. I tried many time using different configuration but always VSP crashed.

So It will be  much appreciated if you could outline steps you have taken to generate mentioned.

I believe that entire  VSP community will applaud to such info.

Cheers

Miro

On Thursday, December 23, 2021, 11:20:16 AM EST, 'Erik Olson' via OpenVSP <ope...@googlegroups.com> wrote:

Jeremy,

I don't think VLM properly models the physics of the slot airflow so there's no point in trying to separate the wing and flap surfaces. IMO the best way to model fowler flaps in VLM is to increase the chord of the wing to account for the flap chord extension. You do have to apply a "lift effectiveness" factor or you'll overpredict the lift augmentation. I wrote a paper that discusses the process in detail. If you go this route you don't have to make separate VSP models for the clean and high lift configurations; you can create both wing components and assign them to sets.

Separating the wing and flap components like in the paper Rob cited is appropriate if you're using a higher-order method such as a panel code or Euler (see this paper). There's a model in the VSP Hangar that implements the geometry modeling process I described in the paper. It includes the custom "Flap Track" component that can be used to specify the translation of the flap.

Erik

https://groups.google.com/d/msgid/openvsp/b338b290-30fb-4a8d-bdd4-e9eaa6ad9cf0n%40googlegroups.com

.

[Miroslav Grulovic]

Thanks Rob, but this is very very confusing.

Comp Geom is producing  only txt, csv and tsv files, and there is no graphic output as per Erik's paper that I could figure out. There is your old presentation for old VSP2 which mentioned CART3D etc....

Also there is Flaightsteram presenation mentioning  VSP COMP GEOM, but with no specifics.

Please explain if you could  how COMP GEEOM output could be transferred to manageable visualized format ( msh, stl, obj ..... etc ) if of course possible.

Thanks in advance

Miro  

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[Miroslav Grulovic]

Hello Erik, happy new year.

I have tried to understand your method of creating flaps while waiting for more comprehensive and elegant way for modeling control surfaces ( ailerons, rudder etc.. )

I am in little project which uses PMARC14, and while experimenting with PMARC14 geometry modeling I came across one of  your article with picture depicted below.

 I have found and downloaded your model from HANGAR  ( File # 415 ) since picture looks like VSP output in CFD stl format as half mesh, I tried  to replicate.

Unfortunately  VSP ( 3.25 & 3.26 ) crashed while executing.

From your published papers  I have concluded that your piece of software HOrDE was used at some point but I could not figure where and how.

 Some times ago I have with NASA permission obtained a copy oh HOrDE but even with your assistance I was not able to even launch it.

Now, at this point of time I am interested only to steps needed to create CFD stl file of half mesh of EET AR=12 ( your model # 415) obviously there is something that I could not figure out all by myself. I tried many time using different configuration but always VSP crashed.

So It will be  much appreciated if you could outline steps you have taken to generate mentioned.

I believe that entire  VSP community will applaud to such info.

Cheers

Miro

On Thursday, December 23, 2021, 11:20:16 AM EST, 'Erik Olson' via OpenVSP <ope...@googlegroups.com> wrote:

Jeremy,

I don't think VLM properly models the physics of the slot airflow so there's no point in trying to separate the wing and flap surfaces. IMO the best way to model fowler flaps in VLM is to increase the chord of the wing to account for the flap chord extension. You do have to apply a "lift effectiveness" factor or you'll overpredict the lift augmentation. I wrote a paper that discusses the process in detail. If you go this route you don't have to make separate VSP models for the clean and high lift configurations; you can create both wing components and assign them to sets.

Separating the wing and flap components like in the paper Rob cited is appropriate if you're using a higher-order method such as a panel code or Euler (see this paper). There's a model in the VSP Hangar that implements the geometry modeling process I described in the paper. It includes the custom "Flap Track" component that can be used to specify the translation of the flap.

Erik

On Sunday, December 12, 2021 at 7:04:05 PM UTC-5 Rob McDonald wrote:

https://groups.google.com/d/msgid/openvsp/b338b290-30fb-4a8d-bdd4-e9eaa6ad9cf0n%40googlegroups.com

.

[Rob McDonald]

1) Build or open a model

2) Run Analysis.... CompGeom...  Execute

2b) A new MeshGeom should be created and can be manipulated in the 3D window.

3) Go to File... Export... and choose your favorite format STL, etc.  Follow the dialog to save.

Rob

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[Miroslav Grulovic]

Thanks Rob, it was working after few attempts.

Following your instructions I was able to make stll export, and later on decent structured mesh suitable for PMARC14 solver.

 Needs some improvements in falps density and wake definition, but basic geometry handling is established.

Cheers

Miro.

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