Experimental evidence of a triadic resonance of plane inertial waves in a rotating fluid

TL;DR

This study provides experimental evidence of triadic resonance in plane inertial waves within a rotating fluid, demonstrating energy transfer mechanisms relevant to rotating turbulence.

Contribution

First experimental validation of triadic resonance of inertial waves in a controlled rotating water tank environment.

Findings

Secondary waves match theoretical resonance predictions

Secondary wavevectors are more normal to the rotation axis

Energy transfer toward quasi two-dimensional motions observed

Abstract

Plane inertial waves are generated using a wavemaker, made of oscillating stacked plates, in a rotating water tank. Using particle image velocimetry, we observe that, after a transient, the primary plane wave is subject to a subharmonic instability and excites two secondary plane waves. The measured frequencies and wavevectors of these secondary waves are in quantitative agreement with the predictions of the triadic resonance mechanism. The secondary wavevectors are found systematically more normal to the rotation axis than the primary wavevector: this feature illustrates the basic mechanism at the origin of the energy transfers towards slow, quasi two-dimensional, motions in rotating turbulence.