A Review on Methods for Measurement of Free Water Surface

Abstract

Turbulent free-surface flows are encountered in several engineering applications and are typically characterized by the entrainment of air bubbles due to intense mixing and surface deformation. The resulting complex multiphase structure of the air–water interface presents a challenge in precise and reliable measurements of the free-water-surface topography. Conventional methods by manometers, wave probes, point gauges or electromagnetic/ultrasonic devices are proven and reliable, but also time-consuming, with limited accuracy and are mostly intrusive. Accurate spatial and temporal measurements of complex three-dimensional free-surface flows in natural and man-made hydraulic structures are only viable by high-resolution non-contact methods, namely, LIDAR-based laser scanning, photogrammetric reconstruction from cameras with overlapping field of view, or laser triangulation that combines laser ranging with high-speed imaging data. In the absence of seeding particles and optical calibration targets, sufficient flow aeration is essential for the operation of both laser- and photogrammetry-based methods, with local aeration properties significantly affecting the measurement uncertainty of laser-based methods.

Three-Dimensional Numerical Simulation of a Two-Phase Supercritical Open Channel Junction Flow

“…The highly dynamic and multiphase nature of junction flows precludes the use of simpler point measurement methods such as manometers [11], wave probes [12,13], point gauges [14], or electromagnetic/ultrasonic devices [15,16] when accurate modeling is desired. The accurate spatial and temporal measurements of complex three-dimensional free surface flows in natural and man-made hydraulic structures are only viable by highresolution non-contact methods such as LIDAR [17,18], laser triangulation [19] or photogrammetric reconstruction from cameras [20] with overlapping fields of view [21]. While photogrammetric methods are still under development, laser-based methods [10,22,23] have been proven as reasonably accurate in the measurement of such hydraulic phenomena.…”

Measurements of Complex Free Water Surface Topography Using a Photogrammetric Method

“…The free water surface flows occurring in these structures are usually turbulent and characterised by a greater or lesser degree of air entrainment, the mechanism of which has been extensively studied [3,4]. Experimental hydraulic measurements, instrumentation, and data processing have evolved over many decades of research and are described in several publications [5,6]. Characterisation of the free surface of slow, steady, and lightly aerated flows is quite straightforward and can be adequately accomplished using well-established point measurement methods, such as U-manometers, point gauges, wave probes, or ultrasonic sensors [6,7].…”

“…Experimental hydraulic measurements, instrumentation, and data processing have evolved over many decades of research and are described in several publications [5,6]. Characterisation of the free surface of slow, steady, and lightly aerated flows is quite straightforward and can be adequately accomplished using well-established point measurement methods, such as U-manometers, point gauges, wave probes, or ultrasonic sensors [6,7]. Nevertheless, measuring the instantaneous free water surface topography of highly complex, aerated, non-homogeneous, and non-stationary flows occurring at high Reynolds and Froude numbers (such as Re > 104 and Fr > 3, respectively) requires a choice of different measurement methods [8].…”

“…Nevertheless, measuring the instantaneous free water surface topography of highly complex, aerated, non-homogeneous, and non-stationary flows occurring at high Reynolds and Froude numbers (such as Re > 104 and Fr > 3, respectively) requires a choice of different measurement methods [8]. Only optical methods based on laser ranging [9,10], laser triangulation [11,12], 3D stereoscopic algorithms [13], and photogrammetric methods [6] have sufficient spatial and temporal resolution for adequate characterisation of complex three-dimensional free surface flows.…”