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Old   May 1, 2014, 02:55
Default CFD to analyse tip stall
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Hedley
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I have a composite plane with NACA 64212.5 root / chord 1.6 meters and a NACA 64210 tip . 3 degrees sweepback and 3 degrees washout / twist . The airplane has a tendancy to drop a wing without warning . I started off trying to understand tip stall aerodynamics and can not find one complete discussion which discusses planform , washout , renyolds number effect SO I thought I should do a CFD analysis of the wing and thought I could take the 3D model and place it in a flow field and then change the angle of attack dynamically around the stalling AOA and in realtime visualise the stall progression - modify wing profile and rinse and repeat .

1. Am I dreaming or can this be done. ?
2. Are there any complete texts on tip stalling ?
3. Does CFD work at the stall ? only 80 KTS and Reynolds number +- 4 Million depending on station .
4. I downloaded SU2 and fell into the black hole of complexity but is this solver capable of doing what I want ?
5. I realized that meshing is as important as the solver so after much assistance from Pointwise downloaded their trial meshing software which looks awesome .
6. Is there a dictionary of jargon throughout the toolchain as when asked questions I do not understand the question let alone the formulation of a response ?
7. Are there books that go through principles and the toolchain without breaking your cranium on the underlying Math ?
8. My current toolchain is - Solid Edge -> .stp 3D model -> Pointwise eval licence 30 days -> SU2 3.1 -> Paraview .
9. I worked through some examples in SU2 eg Onera M6 and get a pretty picture in Paraview but can not find an explanation of what I am looking at in the output visualisation .

In summary I was hoping to see a color shaded visualisation of the stall progression on the wing as AOA changed -I guess this is achieved by looking at the pressure gradient ? If the tip section stalls first then model a leading edge droop and continue until I get some idea of a solution . Tufting the airplane and flight testing would be a long arduous and potentially terminal .
process.

Any responses would be highly appreciated.
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Old   May 1, 2014, 06:26
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1. Yes, it can be done. Why do you have sweepback in such an airplane anyway? I would start with that probably rather than with the airfoil

3. Yes.

As for the stall, you can look at pressure, near wall velocity, skin friction, olflow…

EDIT: also trying and control the tip vortex might be of help here…

Last edited by lovecraft22; May 1, 2014 at 09:23.
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Old   May 1, 2014, 12:09
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Quote:
Originally Posted by lovecraft22 View Post
1. Yes, it can be done. Why do you have sweepback in such an airplane anyway? I would start with that probably rather than with the airfoil

3. Yes.

As for the stall, you can look at pressure, near wall velocity, skin friction, olflow…

EDIT: also trying and control the tip vortex might be of help here…
The airplane is a falcomposite furio - www.falcomposite.com nased on Italian Stelio Frati design the sweepback on leading edge is not severe but from planform view it has 1.6m root chord and 800mm tip chord . This means differing renyolds numbers across span as compared to a plank plus the thinning airfoil section hence the washout or twist . The parent of this plane is the SF260 which needed turbulators placed near tip to compensate for tip stalls that were experienced in the slow flight normally when turning finals with gear down .
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Old   May 1, 2014, 12:47
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Actually it doesn't look like the wing has a sweep angle (as would be reasonable at that cruise speed), it only features taper.
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Old   May 1, 2014, 13:24
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yes that is correct if sweep is defined as a sweepback of the 25% MAC line . thanks
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Old   May 1, 2014, 17:08
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Can CFD to this? Depends. How accurate do you want the results to be?

The wing tip vortex is challenging to model. I don't think there is even agreement on what type of turbulence model to use. If applicable, you'll need to decide between a turbulence model with or without a rotation correction. That puts you on the cutting edge of things.
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Old   May 1, 2014, 17:12
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Oh, in general, turbulence models perform poorly under stalled conditions, and the unset of stall.
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