Non-Contact Acoustic Characterisation of the Dynamic Patterns at the Free Surface of Shallow Turbulent Flows

A recent experimental study characterised the patterns at the free surface of shallow subcritical turbulent flows over a homogeneously rough bed. Detailed wave probe array measurements indicated the pattern of the frequency-wave number spectra at a range of Froude Numbers. Acoustic scattering data was collected simultaneously. The present analysis demonstrates the application of an acoustic technique to obtain the same water surface wave characterisation remotely. The technique reconstructs the free surface elevation based on the measurement of the airborne scattered acoustic field with an array of transducers. Using this method, the dispersion relation of the free surface patterns is measured for a range of flow conditions in a laboratory flume. The study shows the potential of acoustic non-contact measurements for the detailed monitoring of the hydraulic flow conditions in shallow sub-critical turbulent flows.