Control Surface Deflection

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jsale...@gmail.com

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Mar 28, 2023, 5:56:40 PM3/28/23
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Is it possible to deflect a control surface so that when I run Compgeom the output file shows a flap/aileron deflected at a specified angle in the final output file? I am attempting to create a surface mesh that I can run in CFD.

Thank you,
Joe

AGUS SUDARMAWAN

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Mar 28, 2023, 9:45:16 PM3/28/23
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I think is is possible. It is depend on what kind of control surface type you will simulate. At least there are 2 ways.
1. You deflect the control surface part in the aerofoil. By this apporach the control surface and the main aerofoil will be a unit aerofoil. By this approach you will loss the gap between control surface and the main aerofoil. When you call this aerofoil with deflected control surface in the 3D geometry, then you will have wing or tail with deflected control surface. 
2. If you really want to consider the gap between control surface and the main aerofoil then you can define each part (main and control surface) as separate aerofoil. So you weill have aerofoil for main and aerofoil for control surface. We have to save each aerofoil as *.FXS. You have aerofoil, then you can generate 3D geometry. When you already generated 3D geometry for the main part and control surface part, then you can manage the gap and the deflection.
I hope it will help. 

Brandon Litherland

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Mar 29, 2023, 5:41:58 AM3/29/23
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Back in OpenVSP 2, there was an option to set control surface deflections by modifying the airfoil itself in either slat or flap by a percent chord and angle.  This feature has not carried over to VSP3 (yet) for several reasons, one of which is likely how best to meet user's needs based on application (from a gridding/solver viewpoint as well as the type of flap).  The needs of someone trying to run VSPAERO Panel mode will be considerably different than someone wanting to use OpenVSP as the base grid for Fun3D or OVERFLOW.  Erik Olson gave a talk at the 2019 OpenVSP Workshop about modeling high-lift devices in OpenVSP (https://openvsp.org/wiki/lib/exe/fetch.php?media=workshop19:openvsp_workshop_190917_high_lift.pdf).

The recommendations or guidance that we can provide will greatly depend on your application.  What solver are you using?  What gridding software are you using?  
vsp2.3_deflected_airfoil_control.png

jsale...@gmail.com

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Mar 29, 2023, 10:21:11 AM3/29/23
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Thank you for the replies. I am trying to use Compgeom to create .tri files to run in CART3D within an optimization routine. I am using a script to create the aircraft geometry on the fly and then would like to create a .tri for each elevator/rudder deflection case at various deflection angles. Previously I was rotating the entire component to simulate a deflection and that was working well, but I would like to add a hingeline so the deflection geometry is more realistic.

Thanks,
Joe

Brandon Litherland

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Mar 29, 2023, 11:00:17 AM3/29/23
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Taking a step back, are you modeling the control surfaces as separate geometries or trying to deflect a portion of the surface?  OpenVSP's Hinge component is an excellent tool for implementing control surface motion if those are modeled as separate geometries.  It may be worth sharing some images of your models or components so we have a better idea of what you're working on.

jsale...@gmail.com

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Mar 29, 2023, 11:29:07 AM3/29/23
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Hi Brandon,

Thanks for the help. Below is a screenshot of the geometry and attached is the .vsp3 file


test.png

Example_Geometry.vsp3

Rob McDonald

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Mar 29, 2023, 11:31:45 AM3/29/23
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As others have said, it depends on the tools you are using.

Do you need to do finite (large) control deflections, or would you be satisfied with small deflections appropriate for computing control surface derivatives?

Are you using the Cart3D shape optimization framework?  OpenVSP will read and write Cart3D optimization framework *.xddm files natively.  It takes about a two line script to wrap OpenVSP and make it work with the Cart3D framework.  It has been years since I have used any of that stuff, but it should all still work fine.

If you can be satisfied with small deflections, then you can use the control surface subsurface modeling capability in OpenVSP.  You will need to run CompGeom in OpenVSP to imprint the control surface on the wing.  You can then use the adjoint version of Cart3D to calculate control surface derivatives for a 'virtual' control surface deflection.  This will require one Cart3D solve and (typically) six adjoint solves -- one for each quantity you want a derivative of -- three forces and three moments.

It won't really be appropriate to do this in conjunction with a larger optimization study -- OpenVSP's CompGeom is not smart enough to finite difference the geometry and to propagate those derivatives through to the optimization framework.  On the other hand, you could use CompGeom for the wing only (to impress the control surface shape into the wing mesh) and then combine that with the rest of the geometry using Cart3D's Intersect.  That will work as long as you aren't taking any wing variable derivatives.  This is because CompGeom will not guarantee to deliver an identical mesh topology as the wing/control surface changes...


The other approach will be to model the control surfaces as separate components -- they can be built into the model using hinge lines (as Brandon said).  You can then deflect them as much or as little as you want -- if you want to use the adjoint to calculate their derivative, you can just feed the framework the rotation about the hinge line and go from there.


Check out AIAA 2015-1016.  I believe there is a preprint copy available on the OpenVSP website if you don't have access.  Section 4C is a control surface example that you might find interesting.

Rob




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