Wave blocking and partial transmission in subcritical flows over an obstacle

TL;DR

This study combines experimental measurements and theoretical analysis to investigate wave transmission and blocking over an obstacle in subcritical flows, highlighting the importance of transmission coefficients in wave behavior near critical frequencies.

Contribution

It provides a detailed comparison between theory and experiment for wave transmission in subcritical flows, emphasizing the role of transmission coefficients across a range of frequencies.

Findings

Sharp transition between total transmission and wave-blocking observed

Theoretical predictions match experimental data for transition width and frequency

Transmission coefficient significantly affects wave behavior at lower frequencies

Abstract

We study and measure the transmission coefficient of counter-propagating shallow-water waves produced by a wave generator and scattered by an obstacle. To precisely compare theoretical predictions and experimental data, we consider $\sim 25$ frequencies for 5 subcritical background flows, where the maximum value of the Froude number ranges from $0.5$ to $0.75$. For each flow, the transmission coefficient displays a sharp transition separating total transmission from wave-blocking. Both the width and the central frequency of the transition are in good agreement with their theoretical values. The shape of the obstacle is identical to that used by the Vancouver team in the recent experiment aiming at detecting the analogue of stimulated Hawking radiation. Our results are compatible with the observations that have been reported. They complete them by establishing that the contribution of the transmission coefficient cannot be neglected for the lower half of the probed frequency range.