Efficiency of a Digital Particle Image Velocimetry (DPIV) Method for Monitoring the Surface Velocity of Hyper-Concentrated Flows

Donatella Termini,Alice Di Leonardo

doi:10.3390/geosciences8100383

Abstract

Digital particle image velocimetry records high resolution images and allows the identification of the position of points in different time instants. This paper explores the efficiency of the digital image-technique for remote monitoring of surface velocity and discharge measurement in hyper-concentrated flow by the way of laboratory experiment. One of the challenges in the application of the image-technique is the evaluation of the error in estimating surface velocity. The error quantification is complex because it depends on many factors characterizing either the experimental conditions or/and the processing algorithm. In the present work, attention is devoted to the estimation error due either to the acquisition time or to the size of the sub-images (interrogation areas) to be correlated. The analysis is conducted with the aid of data collected in a scale laboratory flume constructed at the Hydraulic laboratory of the Department of Civil, Environmental, Aerospace and of Materials Engineering (DICAM)—University of Palermo (Italy) and the image processing is carried out by the help of the PivLab algorithm in Matlab. The obtained results confirm that the number of frames used in processing procedure strongly affects the values of surface velocity; the estimation error decreases as the number of frames increases. The size of the interrogation area also exerts an important role in the flow velocity estimation. For the examined case, a reduction of the size of the interrogation area of one half compared to its original size has allowed us to obtain low values of the velocity estimation error. Results also demonstrate the ability of the digital image-technique to estimate the discharge at given cross-sections. The values of the discharge estimated by applying the digital image-technique downstream of the inflow sections by using the aforementioned size of the interrogation area compares well with those measured.

Highlights

Accurate knowledge of flow discharge is of crucial importance especially for hydrologist and fluvial geomorphologists
From the “Introduction” and the results reported in previous works [34,35], it is clear that both dimension of the interrogation area and a high dimension of data sample could determine modeling the number of frames and the dimension of the processes too much time-consuming
For the examined case, the estimation error assumes a low and an almost constant value as the number of processed pairs of frames is greater than 1200; the size of the interrogation area plays an important role in the surface velocity estimation

Summary

Introduction

Accurate knowledge of flow discharge is of crucial importance especially for hydrologist and fluvial geomorphologists. In a context of a changing climate, significant hazards associated with both floods and debris or mud flows occur more and more frequently, causing significant changes in topography and river morphology [1]. Traditional techniques usually are based on current-meter measurements (from bridges or set across the channel width) and on the linking of water depth with the discharge through the rating flow velocity curve. Due to the limited accuracy of the current-meter, more modern and accurate instruments, such as Acoustic Doppler Velocimeters (ADV), are used to measure distribution [2,3]. The use of the aforementioned measurement techniques presents many practical difficulties and requires long acquisition times.

Methods

Results

Conclusion