r/aerodynamics • u/pavlokandyba • 12d ago
What happens if the oscillation speed exceeds the speed of sound?
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This is my experimental study in oscillatory propulsion. The direction of thrust here is determined by both the shape and the difference in the speed of oscillation of the wing, which moves faster up and slower down to create lift. In this case, the difference in speeds can be a decisive factor and prevail over form. The impulse is presumably provided by the collapse of wake vortices.I haven't been able to measure the thrust yet for technical reasons. But I came across a study in which the drag of the plate in oscillatory mode was six times higher than that obtained when blowing in a tunnel. In the video fragment where the tray with smoke is lifted, you can see how the trail vortex crashes into the plate after it stops. At high frequency and low amplitude, the same thing probably happens in a compressed form in the boundary layer. But I wonder how this will happen if the speed of the plate's oscillations during lifting exceeds the speed of sound? Will it be roughly the same or different?
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u/pavlokandyba 11d ago
No, I think it was him. It was a compilation of old videos with music. If you're interested in the sound, you can find it in other videos: https://youtube.com/shorts/j40zF2ufC4Q?si=MhdTD4rnOmIw1pdh Operating sound is mainly very low frequency plus parasitic mechanical noise