A (train of) parasail(s) as AWES ?

[PierreB]

The issue of wake effect can be harmful for trains of parasails or other parachute kites or any static kites.

This issue is mentioned on https://repository.tudelft.nl/file/File_4816ada5-be86-4040-b6f7-da37711e3bf9?preview=1 (from the Book of Abstracts from AWEC2024).

I put again an excerpt of this one page PDF:

@PierreB

In the parachute-based AWES, the shape of the parachute and the distance between neighboring parachutes are key factors affecting the flow field, the aerodynamic drag force, and hence the efficiency in harvesting wind energy. It is conceivable that wake separation induced by the parachute cascade could be a major threat to the efficiency of downstream parachutes. However, due to the limited research in this direction, the wake influence on the whole parachute-based AWES unit remains largely unclear.

To tackle this problem, we numerically investigate the thrust coefficient (Ct) of the parachute cascade with a nominal power of 2.4 MW. The impacts of different states of the parachutes (open or closed) and the distance between neighboring parachutes are quantified. The results clearly manifest a large-scale separation flow that significantly damages the performance of downstream parachutes. It is demonstrated that an increase of the distance of neighboring parachutes (to 1000 m) substantially mitigates the wake effect and enhances the lift force of the whole system.

With only one high Cd (at low wind speed) giant unit, the power available in the wind in pumping mode could perhaps be higher than expected (4/27) if we don’t take account of the surface of the disturbed airflow around the parachute.

But the wake effect would lose a lot of energy density due to the need for spacing, if confirmed and depending on the degree.

I wonder if the wake loss from tether-aligned kites in trains would not be even worse than for cascades of crosswind kites like those of Kiteswarms.

Indeed parachute kites block a significant wind area, perhaps more than crosswind kites which work like blades of wind turbines at equivalent wind power.

And it does not seem that the wake effect penalizes the SuperTurbine ™ rotors…