Surface-wave Doppler velocimetry in a liquid metal: inferring the bifurcations of the subsurface flow

TL;DR

This paper presents a novel surface-wave Doppler velocimetry technique for detecting small subsurface flow velocities in liquid metals, providing a simple, sensitive method to analyze flow bifurcations such as the Hopf bifurcation in Galinstan.

Contribution

The paper introduces a new surface-wave Doppler method that directly links surface phase shifts to subsurface flow, enabling easier and more sensitive flow measurements in liquid metals.

Findings

Successfully detected small flow velocities in liquid metal

Identified the Hopf bifurcation in a Kolmogorov flow of Galinstan

Demonstrated high sensitivity and ease of implementation

Abstract

We introduce a velocimetry technique based on the Doppler-shift of surface waves propagating between an emitter and a receiver. In the limit of scale separation between the wavelength and the scale of the flow, we derive the direct connection between the subsurface flow and the measured phase shift between emitter and receiver. Because of its ease of implementation and high sensitivity, this method is useful to detect small velocities in liquid metal flows, where acoustical and optical methods remain challenging. As an example, we study the Hopf bifurcation of a Kolmogorov flow of Galinstan.