[cfd-jg]

Hi all,

I am doing my thesis on aerodynamic shape optimisation of winglets. However, I am struggling to make this work on SU2.

My aim is to minimize drag maintaining lift fixed. The approach I was following is setting an FFD box around the winglet (taking part of the wing as well). Then setting control points, which are allowed to move vertically (so it can adjust the cant angle, radius of rotation of the winglet, AoA and twist). And once I had this working, my plan is to add more complexity letting the control points to move both in x and z directions (to optimise sweep angle as well).

However, I am having issues with implementing this. The problem I am finding is that the objective function (drag) is reduced minimally (only 4th decimal place). I first thought that the problem might be that I had to tune the parameters OPT_GRAD_FACTOR and OPT_RELAX_FACTOR, so I tried it with multiple values (see fig Cd-gradFactor-4.jpg), but none of them reduced drag significantly, while a couple of them diverged.

To give an example of the output: (fig surface_deformed-relaxFactor_600.jpg) this is what the solver generates (first few iterations). This mainly modifies the AoA to reduce drag but not the cant angles much. Also, despite having the 2nd derivative continuity constraint on the configuration file, the output produced is not physically viable. This is because the gradients on the control points next to the boundary between wing-winglet are quite high compared to the rest of control points (seen in fig gradients.jpg).

I was expecting the deformation of the geometry to be larger (at least in cant angle). Interestingly, when I set a larger OPT_GRAD_FACTOR (1E3) the cant angle was deformed significantly (see fig surface_deformed-relaxFactor_1E3.jpg) but maintaining the discontinuity in the boundary between wing and winglet. As a result, the adjoint solution diverges after this point.

I have also tried with different scales in the objective function, but similar results are obtained.

To check if there was something wrong in my configuration file, I checked its validity with the ONERA wing mesh tutorial, and it worked fine (for that mesh and FFD box configuration). Therefore I suspect that my approach may not be the correct one for my case.

I would highly appreciate if anyone more experienced could help or indicate how to approach this optimisation or any suggestion that could help me.


Thank you very much for your help in advance,


The configuration file I am using is: EULER-winglet-shapeOptimisation.txt