Generation of higher harmonic internal waves by oscillating spheroids

Natalia Shmakova, Evgeny Ermanyuk, Jan Bert Flór

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

Oscillating bodies in stratified fluids may emit higher harmonics in addition to fundamental waves. In the present experimental study, we consider higher harmonics of an internal wave field generated by a horizontally oscillating spheroid in a linearly stratified fluid for moderate to high oscillation amplitudes, i.e., scaled oscillation amplitude A/a≥0.5, with a the minor radius of the spheroid. Three different spheroid shapes are tested. The results are discussed in the context of the different theories on the generation of higher harmonics. Higher harmonics are observed at the intersections of fundamental wave beams, and at the critical points of the topography where the topographic slope equals the wave slope. The velocity amplitudes of the fundamental, second, and third harmonic waves grow respectively linearly, quadratically, and with the third power of the scaled oscillation amplitude A/a. Though these amplitudes are generally higher when the object's slope is larger, the increase in amplitude above and below the axisymmetric oscillating objects is found to be due to the effect of focusing. In order to discern the relative importance of the harmonics to the fundamental wave, the horizontal structure of the wave amplitude is measured. The results suggest that the nth harmonic of the internal wave field is associated with a radiation diagram corresponding to a multipole of order 2n, with 2n directions of propagation.

Original languageEnglish
Article number114801
Number of pages13
JournalPhysical Review Fluids
Volume2
Issue number11
DOIs
Publication statusPublished - 7 Nov 2017

Keywords

  • VIBRATING ELLIPTIC CYLINDERS
  • STRATIFIED FLUID
  • PART 1
  • VISUALIZATION
  • TOPOGRAPHY
  • BEAMS
  • FIELD

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