Experimental study on bursting events around a bar in physical model of a braided channel

Lama

et al. 2022

Water

Self Cite

The many hydrodynamic implications associated with the geomorphological evolution of braided rivers are still not profoundly examined in both experimental and numerical analyses, due to the generation of three-dimensional turbulence structures around sediment bars. In this experimental research, the 3D velocity fields were measured through an acoustic Doppler velocimeter during flume-scale laboratory experimental runs over an emerging sand bar model, to reproduce the hydrodynamic conditions of real braided rivers, and the 3D Turbulent Kinetic Energy (TKE) components were analyzed and discussed here in detail. Given the three-dimensionality of the examined water flow in the proximity of the experimental bar, the statistical analysis of the octagonal bursting events was applied to analyze and discuss the different flume-scale 3D turbulence structures. The main novelty of this study is the proposal of the 3D Hole Size (3DHS) analysis, used for separating the extreme events observed in the experimental runs from the low-intensity events.

Section: Analysis Of Three-dimensional Hole Size (3dhs)mentioning

confidence: 88%

Three-Dimensional Hole Size (3DHS) Approach for Water Flow Turbulence Analysis over Emerging Sand Bars: Flume-Scale Experiments

Lama

et al. 2022

Water

Self Cite

“…The skewness coefficients detect the existence of turbulent bursts of high-value presence in velocity signals [17] (Lacey and Rennie 2012). This indicates that the skewness is linked with the turbulent events that are instrumental in the transport of sediments [18] (Bennett and Best 1995). Despite the importance of higher moments of turbulence, still no research is found in the literature related to the turbulence parameters such as turbulent production, skewness coefficients, turbulent kinetic energy flux, and associated bursting events for regions in the vicinity of the mid-channel bar.…”

Section: Introductionmentioning

confidence: 92%

“…The analysis of turbulence in the proximity of the bar is critically important for studying the fluid-and-bar interaction [3,4] ( Khan et al, 2017, Khan andSharma 2018). In this context, an in-depth analysis of the flow turbulence in the vicinity of the bar was performed in the present study.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Turbulent Flow Structure with Its Fluvial Processes around Mid-Channel Bar

et al. 2021

Sustainability

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Researchers have recognized that the successive growth of mid-channel bar deposits can be entertained as the raison d’être for the initiation of the braiding process, which is closely interlinked with the growth, decay, and vertical distribution of fluvial turbulent kinetic energy (TKE). Thus, focused analysis on the underlying mechanics of turbulent flow structures in the proximity of a bar deposit occurring in the middle of the channel can afford crucial scientific clues for insight into the initiating fluvial processes that give rise to braiding. In the study reported herein, a physical model of a mid-channel bar is constructed in an experimental flume to analyze the turbulence parameters in a region close to the bar. Notably, the flow velocity plays an important role in understanding the flow behavior in the scour-hole location in the upstream flow divergence zone as well as near the downstream zone of flow convergence in a mid-channel bar. Therefore, the fluctuating components of turbulent flow velocity are herein discussed and analyzed for the regions located close to the bar. In the present study, the impact of the mid-channel bar, as well as its growth in turbulent flow, on higher-order velocity fluctuation moments are investigated. For near-bed locations, the results show the dominance of ejection events in upstream zones and the dominance of sweep events at locations downstream of the mid-channel bar. In scour-hole sections, the negative value of the stream-wise flux of turbulent kinetic energy and the positive value of the vertical flux of turbulent kinetic energy indicate energy transport in downward and forward directions, respectively. The downward and forward energy transport processes lead to scouring at these locations. The maximum turbulent production rate occurs in the wake region of the bar. The high rate of turbulence production has occurred in that region, which can be ascribed to the process of shedding turbulent vortices. The results show that the impact of the presence of the bar is mainly restricted to the lower layers of flow. The turbulent dissipation rate monotonically decreases with an increase in the vertical distance from the bed. The turbulent production rate first increases and then decreases with successive increases in the vertical distance from the bed. The paper concludes with suggestions for the future potential use of the present research for the practical purpose of examining braid bar occurrences in alluvial rivers to develop an appropriate response through training measures.

“…p ijk = n ijk n ik (7) n ijk is the number of i events followed by j events, then j events followed by k events. n ik is the number of i events followed by k events.…”

Section: Zero-order Markov Chainmentioning

confidence: 99%

“…Several researches, namely [4,[6][7][8], found that the creation and deformation of midchannel bars in an alluvial channel are observed to be transient. Significantly, 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].…”

Section: Introductionmentioning

confidence: 99%

Mid-Channel Braid-Bar-Induced Turbulent Bursts: Analysis Using Octant Events Approach

et al. 2022

Water

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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.