Chapter 27 - The hole size analysis of bursting events around mid-channel bar using the conditional method approach

Abstract

The slow accumulation of midchannel bar deposits is closely related to the turbulent burst phenomenon caused by the interaction between the fluid and bar. This channel process is revealed by researchers to be the raison d’être for initiation of the braiding process. As a result, a focused analysis of the underlying mechanics of turbulent structure near a bar deposit in the midchannel can provide crucial scientific clues for understanding the early fluvial processes that lead to manifestation of braiding. In the work detailed here, a physical model of a midchannel bar is erected in an experimental flume to analyze the turbulence burst in an area near to the bar. The Reynolds stress is calculated using the conditional averaging approach. The hole size concept is used to separate the high intensity events from the low intensity events. The effect of hole size on the bursting events is also analyzed in this chapter. The value of occurrence probability of even events increases from 0.30 to 0.36 at scouring region. The value of occurrence probability of odd events increases from 0.28 to 0.32 at depositional region. The even events are dominant at zones upstream of bar, and odd events are dominant at zones downstream of bar, and the above results indicate that the dominance of dominant events increases with value of hole size increase. The temporal structure of quadrant events is also analyzed in this chapter. The frequency of quadrant events occurrence decreases with increase in value of hole size. This clearly indicates that the high intensity quadrant events have lesser frequency of occurrence. The Q1 events persist up to time period of 0.2 s at zones downstream of midchannel bar. This indicates that the Q1 events are temporally more stable in zones downstream of the midchannel bar. The depth-wise distribution of Reynolds stress is analyzed in this study. The maximum value of Reynolds stress of Q2 and Q4 quadrant is 3.5 for 2R experimental run, and its value increases to 5 for 4R experimental run. The above results show that increase in the size of bar leads to the generation of more turbulence in its vicinity. This indicates that the increase in size of bar creates a zone which is more susceptible to deposition in its vicinity.