|MadSci Network: Physics|
I think that you're exactly right. The hot gauze will cause air to rise in the tube, and the rising air will form turbulent eddies. The eddies will most likely set up a standing wave in the tube. Can you estimate the frequency/wavelength from the tone, and does it correspond to a standing wave for the tube? This may not be easy, because turbulent eddies will most likely excite numerous resonances in the tube. For a 1 m tube, acting as a resonator with one end open, the first four resonances are at 85, 255, 408, and 595 Hz (Halliday, Resnick & Walker, or any other intro physics text).
Another test would be to see if the tone either changes goes away when the tube is held horizontally or upside down. The form of any eddies should be different then, or even exiting through the other end of the tube.
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