Velocimetry Based on Self-Generated Surface Wave Patterns

Hao-Che Ho,Ying-Tien Lin,Marian Muste

doi:10.3390/w12092342

Hao-Che Ho, Ying-Tien Lin + Show 1 more

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https://doi.org/10.3390/w12092342

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Abstract

This paper introduces an image analysis technique applied to an artificially-created disturbance at the free surface of a moving water body as a means of quantifying the average velocity of the water stream for shallow flows. The disturbance was created by a thin object penetrating the free surface with different submerged distances. A V-shaped wake pattern was created by the object of interest through its variation with the water body velocity, the submergence and shape of the piercing body. The angle of the wake pattern decreased with the increase of the velocity for a depth-based Froude number ranging from 0.15 to 0.96. The proof-of-concept experiments presented in this paper, therefore, are usable to quantify the velocity based on the wake angle only in subcritical flow conditions. The results showed the shape of the wake was only slightly influenced by the shape of the object geometry and its submergence. Observations on various types of surface wakes have been documented before, but it is the conversion of these observations into a relatively inexpensive and robust method to estimate the velocity of the moving body that is deemed innovative.

Highlights

The methodology for velocity estimation described in this paper pertains to the family of approaches for determining velocities in open-channel flows with the ultimate target for estimation of discharges
The effect of the submergence (d) of the rod on the wake angles was studied in a 0.6 m-wide
The laboratory experiments summarized in this paper illustrate that the Kelvin wake angle for a thin object piercing the free surface of a moving water stream decreases as the velocity increases for all

Summary

Introduction

The methodology for velocity estimation described in this paper pertains to the family of approaches for determining velocities in open-channel flows with the ultimate target for estimation of discharges. From this perspective, it is useful to call upon one of the classifications of these methods that categorize them as intrusive or nonintrusive approaches. The advent of acoustic velocimetry has enabled us to acquire more efficient velocity measurements in the water column by placing the probes (such as an acoustic Doppler current profiler) in contact with the free surface [1,2]. Irrespective of their operating principle (e.g., mechanical, electrical or acoustic), probes that require submergence or contact with the water are associated with deployment of personnel and/or floating platforms (e.g., boats or instrument-attached rafts) in the stream, making their operation more complicated and at times even hazardous.

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