Abstract
We present an experimental study of resonant generation of superharmonic internal waves as a result of interaction between horizontally propagating vertical internal wave modes and at frequency in a uniformly stratified finite-depth fluid. Thorpe [J. Fluid Mech. 24, 737 (1966)] has shown theoretically that modes and at frequency and mode at frequency are in triadic resonance at specific values of . We demonstrate the occurrence of this triadic resonance by forcing a primary wave field of modes and at various using a novel internal wave generator, and observing the spontaneous growth (or lack thereof) of the superharmonic mode at frequency . A superharmonic wave field with a predominantly mode- structure is observed over a finite range of frequency () around the resonant value, where is the uniform buoyancy frequency. The spatial growth of the superharmonic wave field is then quantitatively measured, to subsequently compare with the predictions from amplitude evolution equations at resonance at various forcing amplitudes, thereby validating this model. It is furthermore shown that a large-scale spatial evolution of the wave field is more suited to describe our experiments than the slow temporal evolution approach. The paper concludes with a brief discussion of viscous effects.
5 More- Received 11 December 2019
- Accepted 7 July 2020
DOI:https://doi.org/10.1103/PhysRevFluids.5.074804
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