page_title: Physics of whistles
section_title: Ring tone
hierarchical_section_title: Physics of whistles / Dipole-like whistles / Ring tone
caption_attribution_description: English: Ring sound
context_page_description: A whistle is a device that makes sound from blowing air. The physical theory of the sound-making process is an example of the application of the science of fluid dynamics. Knowledge of the geometry, dimensions and fluid properties can allow prediction of the properties of the whistle. The principles relevant to whistle operation also have applications in other areas such as fluid flow measurement.
context_section_description: The word "ring" here refers to the shape and not to the bell sound. The flow from a circular orifice impinging on a toroidal ring of the same diameter as the orifice will result in a tone; it is called a ring tone. It is similar to the hole tone described above, except that because the plate was replaced by a ring, a fundamental change in the resultant sound field occurs. Small disturbances at the ring feed back to the orifice to be amplified by the flow instability (class I). The unstable flow creates a set of symmetric (ring) vortices that later impinge on the physical ring.
  The passage of a vortex by the ring is shown schematically in the figure on the right in three steps. The flow vectors in the figure are merely suggestive of direction.
  When two vortices are equidistant from the ring, one being beyond and the other approaching, the net circulation around the ring is zero; the null point for the flow oscillation. Each vortex creates a circular (ring) flow field whose axis varies slightly from the vertical as it passes. The figure suggests that the main component of the force on the physical ring is in the direction of the jet flow. If the vortex is a true ring (all parts are in phase), a dipole sound field directed along the jet axis is created.
  The figure also suggests that there is a lateral component of force, which can only be interpreted as a weak radial dipole. Experiments have been performed on the ring tone. The lower figure on the right shows the relationship of frequency to Reynolds number. If the Strouhal number were graphed instead of the frequency, it would have shown that contours were reasonably constant similar to those for the hole tone. Close examination of the data in the figure showed a slight negative dependence of Strouhal number on Reynolds number.
  It appears that this whistle has only two stages. The sound field was measured and clearly indicated a dipole, whose axis was aligned with the jet axis. Since there were no reflecting surfaces near the source, the data also indicated that a weaker radial dipole component also existed. Such a field can only exist if there is a time delay at a distant point between each of the force components.
caption: Ring flow field
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