A. W. Nolle
Dept. of Phys., Univ. of Texas at Austin, Austin, TX 78705
Jets of stream velocity 8 to 20 m/s, 0.5 to 1.5 mm thick, are deflected by lateral flow either localized at the orifice or distributed as in an organ pipe. Synchronous hot-wire samples yield smoothly oscillating jet profiles to a downstream distance of some eight times the thickness. The frequency is 50 to 900 Hz. In disagreement with theory, the phase velocity of jet centerline displacement does not fall with decreasing frequency. For a parabolic velocity profile, this phase velocity rises near the orifice, remaining well defined. For a tophat profile the entry-zone velocity rise is more severe, but the phase velocity becomes ambiguous because the shear layers are unmerged, with out-of-phase varicose oscillations as predicted by Crighton. Lateral variation of velocity modulation phase is quite different for the two profiles. The phase of jet displacement relative to the acoustic pressure gradient is examined. The top-hat entry profile occurs in most flue organ pipes. A pipe with parallel-wall flue, giving the less usual parabolic profile, is demonstrated. In the zero-frequency limit, also studied, jet deflection is predictable from the momentum fluxes. Zero-frequency deflection produces jet self-centering in stopped pipes.