Investigation of Coherent Flow Turbulence in the Proximity of Mid-channel Bar

다국어 초록 (Multilingual Abstract)

The turbulent flow characteristics in the vicinity of mid-channel bar are studied in this paper. The velocity is measured with the help of the acoustic Doppler velocimetry (ADV). Fractal modelling is done for analysing the fractal nature of bursting events. The conditional Reynolds stress structure was analysed by using the quadrant technique. Decomposition of Reynolds stress help in studying the distribution of stress among the four quadrants. The hole-size concept is utilized for segregating the extreme bursting events from the low intensity events. Variation of quadrants stresses with the hole-size is analysed. The result of hole-size study indicates that the extreme turbulent burst is produced by the mid channel bar. The new parameter inclination ratio is evolved in this research to reflect streambed elevation changes. The results indicate that the high-level turbulence is generated at region near upstream end of mid-channel bar. The presence of mid-channel bar causes the critical changes to the turbulent structure of flow, where high Reynolds stresses are generated at region near upstream region of mid-channel bar. Third order moments are computed for vertical lines in the proximity of mid-channel bar. High value of third order moments for bar condition indicate that the intense turbulent mixing and momentum exchange take place.

참고문헌 (Reference)

1 L. Cea, "Velocity measurements on highly turbulent free surface flow using ADV" Springer Science and Business Media LLC 42 (42): 333-348, 2007

2 R. I. Ferguson, "Understanding braiding processes in gravel-bed rivers: progress and unsolved problems" Geological Society of London 75 (75): 73-87, 1993

3 M. W. Schmeeckle, "The role of velocity, pressure, and bed stress fluctuations in bed load transport over bed forms: numerical simulation downstream of a backward-facing step" Copernicus GmbH 3 (3): 105-112, 2015

4 NORMAN D. SMITH, "The Braided Stream Depositional Environment: Comparison of the Platte River with Some Silurian Clastic Rocks, North-Central Appalachians" Geological Society of America 81 (81): 2993-3014, 1970

5 Sharma, N., "The Brahmaputra basin water resources" Springer 229-260, 2004

6 O. COCEAL, "Structure of turbulent flow over regular arrays of cubical roughness" Cambridge University Press (CUP) 589 : 375-409, 2007

7 Saeed Jafari Mianaei, "Spatio-temporal variation of transition probability of bursting events over the ripples at the bed of open channel" Springer Science and Business Media LLC 22 (22): 257-264, 2008

8 Victor Sapozhnikov, "Self-Affinity in Braided Rivers" American Geophysical Union (AGU) 32 (32): 1429-1439, 1996

9 Jonathan M. Nelson, "Role of Near-Bed Turbulence Structure in Bed Load Transport and Bed Form Mechanics" American Geophysical Union (AGU) 31 (31): 2071-2086, 1995

10 Leopold, L., "River channel patterns" 3 (3): 347-354, 1957

11 Maarten G. Kleinhans, "River channel and bar patterns explained and predicted by an empirical and a physics-based method" Wiley 36 (36): 721-738, 2011

12 Mohamed Gad-el-Hak, "Reynolds Number Effects in Wall-Bounded Turbulent Flows" ASME International 47 (47): 307-365, 1994

13 Keshavarzi, A., "Probability analysis of instantaneous shear stress and entrained particles from the bed" 2002

14 Ali Reza Gheisi, "Markovian–Octant analysis based stable turbulent shear stresses in near-bed bursting phenomena of vortex settling chamber" Springer Science and Business Media LLC 6 (6): 549-572, 2006

15 PHILIP J. ASHWORTH, "MID-CHANNEL BAR GROWTH AND ITS RELATIONSHIP TO LOCAL FLOW STRENGTH AND DIRECTION" Wiley 21 (21): 103-123, 1996

16 Peter E. Ashmore, "Laboratory modelling of gravel braided stream morphology" Wiley 7 (7): 201-225, 1982

17 P. Saha, "Investigation of coherent structures in a turbulent channel with built-in longitudinal vortex generators" Elsevier BV 104 : 178-198, 2017

18 Vladimir Nikora, "Flow Turbulence over Fixed and Weakly Mobile Gravel Beds" American Society of Civil Engineers (ASCE) 126 (126): 679-690, 2000

19 S. A. SCHUMM, "Experimental Study of Channel Patterns" Geological Society of America 83 (83): 1755-1770, 1972

20 Coraline L. Wintenberger, "Dynamics of nonmigrating mid-channel bar and superimposed dunes in a sandy-gravelly river (Loire River, France)" Elsevier BV 248 : 185-204, 2015

21 Peter Ashmore, "Confluence scour in coarse braided streams" American Geophysical Union (AGU) 19 (19): 392-402, 1983

22 Peter Ashmore, "Channel Morphology and Bed Load Pulses in Braided, Gravel-Bed Streams" Informa UK Limited 73 (73): 37-52, 1991

23 Md. Amir Khan, "Analysis of turbulent flow characteristics around bar using the conditional bursting technique for varying discharge conditions" 대한토목학회 22 (22): 2315-2324, 2018

24 Kyle B. Strom, "ADV Measurements around a Cluster Microform in a Shallow Mountain Stream" American Society of Civil Engineers (ASCE) 133 (133): 1379-1389, 2007

25 A. Scotti, "A fractal model for large eddy simulation of turbulent flow" Elsevier BV 127 (127): 198-232, 1999