Fluid Flow at a Small Hole due to Vibration

Abstract

I SHOULD like to acknowledge my indebtedness to Prof. Andrade¹ for directing my attention to the work, of H. Sell². As a result, I have made a careful examination, by means of strong lateral illumination, of the way in which the smoke particles enter and leave the orifice in the resonator. There is no doubt about the general accuracy of H. Sell's explanation, and this is particularly well demonstrated when the smoke is made to issue in the space between two parallel plates of glass kept apart by a distance piece the thickness of which is approximately that of the diameter of the orifice. The smoke particles can then be seen as bright dots on a dark ground, and their paths easily traced. As well as the back-flow near the surface of the resonator, vortex motion occurs. If, however, the smoke be allowed to issue from a V-shaped mouthpiece formed by sealing two flat pieces of glass between the plates, then, provided the excitation is not too powerful, both the vortex motion and the back-flow cease. There now occurs what appears to the eye as a slow steady motion of the smoke outwards. Examination of the particles with a low-power microscope shows them, however, no longer as dots but as little lines, so that a vibratory motion is superimposed on the general forward motion.