Working Principles of Lamina(r) flow thermoacoustic engines

[kessler1]

I'm assuming you're familiar with these engines a few people on youtube are experimenting with. If not, here's a link:
https://www.youtube.com/watch?v=wg96lDw7sNw

There doesn't seem to be a proven or agreed upon mechanism of action for these devices. At first glance, it's peculiar to me how the stack is being heated on the opposite end that a normal thermoacoustic engine's stack is heated. Does anybody know what's going on here? My knowledge on this subject is limited I admit, but I've been reading Gregory Swift's Thermoacoustics, and the reasoning for heating the stack on the side facing the closed end is clear: standing waves have peak pressure on the ends and peak velocity in the center, and we want to inject heat at high pressure and reject at low pressure. So what's going on here? Is this simply a sterling engine that resonates and not a thermoacoustic engine? Are we pumping a higher harmonic? Is there a complicated interference pattern going on that's hard to realize?

Any ideas and explanations will be greatly appreciated. I've never been so stumped!

[VincentG]

Here's my two cents.

There are so many factors at play with these types of engines that all influence the resonant frequency and have kept me from putting much thought into them. The speed of the piston, the heat itself, the length of the tube, the steel wool vibrating due to heat and airflow, standing waves, pressure waves, etc.

I think the rpm of the crankshaft should be measured, and a digital tuner or microphone can be used to help find out which order of harmonic is prevailing, as well as what effects what and how to harmonize them all together. If we can also add small lightweight and very responsive diaphragms or manometers at different points along the tube, a high speed camera could be used to follow the pressure waves. There are also some effective speaker tuning methods that simply use rice or beads to visualize the harmonics. Perhaps this could help as well.

LES_Thermodynamics seems to have made the most progress with similar engines.

[Tom Booth]

There is a lot of precise measurement and mathematics involved in creating standing waves, in a tube full of air, like the tubes of a wind chime for example:


https://youtu.be/rqrsNYLofCo?si=jQBdma_HvDbnjpZk


However, I can't see a wind chime actually working if there was a cork in one end and the other end was stuffed full of steel wool.

[Bumpkin]

I could well be wrong, but the lower frequency and the nozzle design of that engine suggests to me that it is a thermal lag engine. Tibsim’s site has some interesting thermoacoustic stuff. The videos at the bottom are interesting.
https://tibsim-thermoacoustics1488.blogspot.com/

Bumpkin

[Fool]

I think they work with a similar principal to the jam jar jet engine, and a put put boat.