Abstract
In a laboratory, a model of a mid-channel bar is built to study the turbulent flow structures in its vicinity. The present study on the turbulent flow structure around a mid-channel bar is based on unravelling the fluvial fluxes triggered by the bar’s 3D turbulent burst phenomenon. To this end, the three-dimensional velocity components are measured with the help of acoustic doppler velocimetry (ADV). The results indicate that the transverse component of turbulent kinetic energy cannot be neglected when analyzing turbulent burst processes, since the dominant flow is three-dimensional around the mid-channel bar. Due to the three-dimensionality of flow, the octant events approach is used for analyzing the flow in the vicinity of the mid-channel bar. The aim is to develop functional relationships between the stable movements that are modelled in the present study. To find the best Markov chain order to present experimental datasets, the zero-, first-, and second-order Markov chains are analyzed using the Akaike information criterion (AIC) and the Bayesian information criterion (BIC). The parameter transition ratio has evolved in this research to reflect the linkage of streambed elevation changes with stable transitional movements. For a better understanding of the temporal behaviors of stable transitional movements, the residence time vs. frequency graphs are also plotted for scouring as well as for depositional regions. The study outcome herein underlines the usefulness of the octant events approach for characterizing turbulent bursts around mid-channel bar formation, which is a precursor to the initiation of braiding configuration.
Highlights
The river Brahmaputra is well-known on the Indian subcontinent for its extreme braided condition
A new parameter has been added in this study; the transition ratio, which has been developed to depict the relationship between streambed elevation changes and steady transitional movements of 3D turbulent bursts using octant events
A key finding yielded from the present research highlights that the transverse component of the turbulent burst phenomenon has a significant contribution to turbulence generation for points present in close proximity to the bar
Summary
The river Brahmaputra is well-known on the Indian subcontinent for its extreme braided condition. As observed by [1,2,3,4,6], the braiding behavior in alluvial streams originates from the initiation of the mid-channel bar, and that is the reason for selecting its study in the present research [9]. The authors of [10,11] had performed experiments in a turbulent open channel flow They studied the space–time correlation structure of the bursting events using the conditional sampling technique. Making 3D measurements of relevant micro-scale variables in a large prototype alluvial river to get insights into the internal fluvial domain for correctly studying turbulent bursts during channel-creating or -deforming flood-flows is neither practicable nor viable. A new parameter has been added in this study; the transition ratio, which has been developed to depict the relationship between streambed elevation changes and steady transitional movements of 3D turbulent bursts using octant events
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