"Optimisation of a Multi-Element Airfoil for a Fixed-Wing Airborne Wind Energy System"

From 23 papers on AWE published in open access journal Energies :


Airborne wind energy systems benefit from high-lift airfoils to increase power output. This paper proposes an optimisation approach for a multi-element airfoil of a fixed-wing system operated in pumping cycles to drive a drum-generator module on the ground. The approach accounts for the different design objectives of the tethered kite’s alternating production and return phases. The airfoil shape is first optimised for the production phase and then adapted for the requirements of the return phase by modifying the flap setting. The optimisation uses the multi-objective genetic algorithm NSGA-II in combination with the fast aerodynamic solver MSES. Once the optimal shape is determined, the aerodynamic performance is verified through CFD RANS simulations with OpenFOAM. The resulting airfoil achieves satisfactory performance for the production and return phases of the pumping cycles, and the CFD verification shows a fairly good agreement in terms of the lift coefficient. However, MSES significantly underpredicts the airfoil drag.

Extracts from page 11:

3.1.1. Production Phase […]

The polars indicate a maximum lift coefficient of 𝐶L,max=2.95, which leads to a design lift coefficient of 𝐶L,des=2.36.[…]

3.1.2. Return Phase

As shown in Figure 15, the airfoil optimised for the production phase reaches a 𝐶L,min≈0.5 at 𝛼=−10°.

From page 14:

Figure 20. Verification of the lift and drag polars for the airfoil optimised for the production phase with the flap down.

Figure 21. Verification of the lift and drag polars for the airfoil optimised for the return phase with the flap up.

High lift by using multi-element airfoil was discussed in High lift coefficient and biplane kite flying in hovering (fly-gen) mode, but now it is a monoplane flying in bounding (reeling, pumping, yo-yo…) mode, and Kitemill is involved in this study. Thus the next steps for Kitemill look promising.

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Good detective work, Pierre:
This illustrates what I was wondering with the spinning sausage shape - what about just using an airfoil.
I must admit though, I’m perplexed that the polars graphed for the production and return phase look so similar. Not sure how “promising” it looks for any company though, versus just more idle musing about possible configurations.

Doug, you never read the information given and therefore only spout negative nonsense about almost all subjects.

The difference between the polars on Figures 20 and 21 is quite huge, when considering the given angle of attack of -10° during the return phase.

Well as someone who had a track record in AWE and manufacturing wind turbines before the current hype-cycle got started, I could clearly see the field of AWE in general was pretty-much clueless about wind energy, and it was not always necessary to read every word to see when some proposal or project was going nowhere. I think after 15 years of nothing running on a regular basis, my off-the-cuff opinions been confirmed.

However you may note that I’ve always expressed dismay about why there were so few examples of kites pulling boats, having been an early enthusiastic proponent, and I did just include a video of a pretty fast catamaran being pulled by a kite with those two guys and even dad on board. That looks promising. The yacht pulled by a kite - looked like it was going too slow to even generate a wake. I’m now thinking the shots of the same boat using no kite, with a thick propeller wake, were taken with the diesel engine running - who knows…

Beyond that, it is easy for me to miss something. I’m still taking your subject matter seriously here. Obviously, some things escape my attention, and I guess this is one example, because I don’t see what you are saying. Oh well, I know a lot, but I don’t know everything. The graphs look very similar to me. Maybe I’m missing a finer point? Not sure why I’m not seeing what you are saying. :slight_smile:

Within a purely scientific context.

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3 posts were merged into an existing topic: Preprint: Towards a gigantic Magnus balloon with motorized belts

Maybe also in other ways. We’ll see

Doug, you are fully off-topic. Have you read the publication linked in the initial topic? The answer is no, as usual. I don’t care about your general considerations. So I put it again: