Fluid Simulations in the Kitchen Sink

In an age of ultra-powerful GPUs and cheap processors, computational techniques which were once only available to those with a government-sized R&D budgets are now available to the everyday hacker. An example of industry buzzword turned desktop software is the field of “computational fluid dynamics”, which put simply allow modeling how gasses or liquids will behave when moving through a cavity under specific conditions. Extensive utilization of these fluid simulations are often cited as one of breakthrough techniques which allowed SpaceX to develop their engine technology so rapidly when compared to Apollo and Shuttle era methods.

But just because anyone with a decent computer has access to the technology used for developing rocket engines doesn’t mean they have to use it. What if you prefer to do things the old-fashioned way? Or what if, let’s me honest, you just can’t figure out how to use software like Autodesk CFD and OpenFOAM? That’s exactly where [Desi Quintans] found himself when developing GUST, his cooling duct for i3-type 3D printers.

[Desi] tried to get the big name fluid simulation projects working with his prototype designs for an improved cooling duct, but had no end of trouble. Either the learning curve was too steep, or the simulation wasn’t accurate enough to give him any useful data. But remembering that air is itself a fluid, [Desi] took his simulation from the computer to the sink in order to better visualize what his cooling duct was doing to the airflow.

[Desi] printed up a box with a hole in the bottom that would connect up to his nozzles under test. As the volume of water in the box would be a constant between tests, he reasoned that this would allow him to evaluate the different nozzles at the same pressure. Sure enough, he found that the original nozzle design he was using caused chaotic water flow, which backed up what he was seeing in his experiments when mounted onto the printer.

After several iterations he was able to tame the flow of water by using internal baffles and fins, which when tested in water created something of a laminar flow effect. When he tried this version on the printer, he saw a clear improvement in part cooling, verifying that the behavior of the air and water was close enough for his purposes.

We’ve seen other projects that successfully used fluid simulations in their design before, but the quick and dirty test procedure [Desi] came up with certainly has its charms.

Compressed Air Levitation and the Coanda Effect

What do you want to levitate today? [Latheman666] uses his air compressor to make all kinds of stuff float in mid air. Light bulb, key chain, test tube, ball bearing, tomato… pretty neat trick to try in your shop.

It is interesting to see what physics explain this behavior. The objects do not float just because they are pushed upwards by the airflow, that would be an unstable equilibrium situation. Instead, they obtain lift in a very similar way as the wings of an airplane. Not all objects will levitate using this trick: the object has to be semi-spherical at the top.

[Applied Science] nicely shows this behavior by levitating a screwdriver first, then an identical object but with a flat top. The flat top screwdriver fails to levitate. The curvature provides the path for a smooth airflow, because of the Coanda effect, creating a zone of low pressure at the top, making the situation analogous to that of an airplane wing. Therefore, for this to work, you need an object with some kind of airfoil shaped surface. Another great demonstration is that of [NightHawkInLight], using a high speed camera.

A very impressive experiment that needs nothing more than an air compressor!, we are sure you will try it next time you work with one. For more on this topic of levitation with air streams, check the ping pong ball levitation machine.

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Peculiar Fluid Dynamics Creates Hot and Cold Air

We’re fascinated by things with no moving parts or active components that work simply by virtue of the shape they contain — think waveguides and resonators for microwave radiation. A similarly mystical device from the pneumatics world is the Hilsch Vortex Tube, and [This Old Tony] decided to explore its mysteries by whipping up a DIY version in his shop.

Invented in the 1930s, vortex tubes are really just hollow tubes with an offset swirl chamber. Incoming compressed air accelerates in the swirl chamber and heads up the periphery of the long end of the tube, gaining energy until it hits a conical nozzle. Some of the outer vortex escapes as hot air, while the rest reflects off the nozzle and heads back down the pipe as a second vortex inside the outer one. The inner vortex loses energy and escapes from the short end as a blast of cold air – down to -50°C in some cases. [Tony]’s build doesn’t quite approach that performance, but he does manage to prove the principle while getting a few good-natured jabs into fellow vloggers [AvE] and [Abom79].

We’ve covered vortex tubes before, but as usual [Tony]’s build shines because he machines everything himself, and because he tries to understand what’s making it work. The FLIR images and the great video quality are a bonus, too.

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Brain controlled fluid simulation

Here’s another video demo of [Eric]’s Besmoke interactive fluid simulation that we covered earlier. It was put together for the BIL Conference last weekend. This time around he’s strapped the iPhone to his head (complying with California’s handsfree laws). To make things interesting, he’s also added OCZ’s Neural Impulse Actuator to provide brainwave input.

Besmoke – fluid dynamics

Besmoke is a fluid dynamics engine. It is compatible with any multitouch system, as well as the accelerometer in an iPhone. It also accepts audio input. The audio input can turn it into a fancy music visualizer that would even work with live or acoustic music. Different frequencies cause fluid to be injected from different “emitters”. There’s great info on his page, including the papers that he based this off of. We’ve covered [Eric]’s work before with his election party light system.