Computational Fluid Dynamics

Although we often think that we got certain aspects of aerodynamics pretty much licked at this point, details like the optimal shape of a propeller remains hotly debated, both in- and outside of academia. This also includes wilder designs like toroidal propellers that even after more than a hundred years are still mostly just being evaluated. Recently [Neuronautics] took a shot at figuring out whether toroidal propellers even make sense.

In order to do this, first an efficiency baseline was established using a conventional and highly optimized propeller. After scanning it in to get its exact geometry and running it through a computational fluid dynamics (CFD) simulation, the software spat out a number of about 73%.

This left figuring out an optimized shape for the toroidal propeller to pit against it. While you can absolutely brute-force the seventeen shape parameters being considered here and test them in CFD, this would take insanely long. The hack here is to use multiple reference frame (MRF) to drastically speed up the selection process, though even then it still took two months. An example of using MRF with regular propellers is discussed in a 2019 paper by [Randi Franzke] et al. in Energies.

Although MRF saves a lot of simulation time, you still end up with a lot of data that has to be analyzed for interesting patterns. For this [Neuronautics] trained a artificial neural network to automate filtering the many options for the most optimal ones, until converging onto a single design.

This G1401 design was the lucky winner, though with only a simulated 62.9% efficiency. Subsequently the one aspect that had been left unchanged was also iterated through, in the form of many different airfoil shapes until the final design appeared.

This design was then 3D printed in resin, which showed the first hurdle with the selection process, in that the printed versions were too thin and flexible to be usable as propellers. Cue many hours of manual tweaking of the design to make it actually printable.

Although the final design didn’t exceed 62% efficiency in a final test, the comment section to the video rightfully points out that the comparison was between a commercially made propeller and a DIY resin-printed one, which adds a whole other batch of variables. That said, it’s unlikely that there’d have been an obvious improvement either way, otherwise we’d already have seen toroidal propellers pop up everywhere on drones and aircraft.

Continue reading “Pitting A CFD-Optimized Toroidal Propeller Against A Conventional One” →

Computational Fluid Dynamics, or CFD, and is applied to everything from aircraft design to how good of a wing a new skyscraper will be. Of course, the science of building airfoils is much older than CFD, leading to the question of how airfoil design was done before computers.

The answer, of course, is a wind tunnel. Walk around a few very good air museums, and you’ll find wind tunnels ranging from the long wooden boxes built by the Wright brothers to fantastic plywood contraptions that are exceptionally interesting to woodworkers.

[Joel] needed final project as an upcoming aeronautical engineer, but he wanted his project to be something physical, and a tool that could be used again. He decided to build a wind tunnel that’s also his entry for The Hackaday Prize.

This wind tunnel isn’t a gigantic device the size of a building. The very first wind tunnels were simple devices just a few meters long. With a fan at one end, a section to stabilize the wind, a chamber, and a place for the air to go, it’s also a very simple device. Just because something is simple doesn’t mean anyone has built one recently, though: [Joel] couldn’t find anyone who built a wind tunnel with step-by-step instructions. This project is just that – an Open Source wind tunnel.

The design of this wind tunnel is simple enough, built out of fiberglass with relatively simple molds. The design can be adapted to various electric fans, and the most fun part of the build – the smoke machine – is already complete.