Hostname: page-component-745bb68f8f-v2bm5 Total loading time: 0 Render date: 2025-02-03T00:23:41.415Z Has data issue: false hasContentIssue false
  • English
  • Français

Flow separation at convex banks in open channels

Published online by Cambridge University Press:  17 August 2015

K. Blanckaert
K. Blanckaert*
Affiliation:
Ecole Polytechnique Fédérale Lausanne (EPFL), School of Architecture, Civil and Environmental Engineering (ENAC), Laboratory of Hydraulic Constructions (LCH), Station 18, 1015 Lausanne, Switzerland
*
†Email address for correspondence: koen.blanckaert@epfl.ch
Get access Rights & Permissions [Opens in a new window]

Abstract

Laboratory experiments in an open channel bend provide insight into the physics of convex bank flow separation occurring in a variety of channel configurations, including confluences and bifurcations. The edge of the zone of flow separation is characterized by a shear layer, enhanced velocity gradients, tke, turbulent shear stresses and reversal of the streamwise vorticity and vertical velocity. The latter result from turbulence-induced secondary flow near the convex bank. When bankline curvature abruptly increases, flow tends to move away from the convex bank along a straight path, as represented by the inertial forces – including the centrifugal force – in the transverse momentum equation written in curvilinear coordinates. Mass accumulation at the opposite bank leads to a transverse tilting of the water surface, and a pressure gradient towards the convex bank that causes the flow to change direction. The pressure gradient force lags spatially behind the inertial forces, which promotes flow separation. Flow separation typically occurs downstream of the location of maximum change in the bankline curvature, because an abrupt increase in bankline curvature also leads to water surface gradients that cause local flow redistribution towards the convex bank that opposes flow separation. The zone of convex bank flow separation is shaped by the secondary flow induced by streamline curvature and turbulence. The latter is conditioned by the production rate of tke, which crucially depends on the accurate description of the Reynolds stresses. Hydrodynamic, geometric and sedimentologic control parameters of convex bank flow separation are identified and discussed.

JFM classification

Boundary Layers: Boundary layer separation Geophysical and Geological Flows: River dynamics Geophysical and Geological Flows: Shallow water flows
Type
Papers
Information
Journal of Fluid Mechanics , Volume 779 , 25 September 2015 , pp. 432 - 467
Check for updates
Copyright
© 2015 Cambridge University Press 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Abad, J. D. & Garcia, M. H. 2009 Experiments in a high-amplitude Kinoshita meandering channel: 1. Implications of bend orientation on mean and turbulent flow structure. Water Resour. Res. 45, W02401.Google Scholar
Bagnold, R. A.1960 Some aspects of the shape of river meanders. US Geological Survey Professional Paper 282-E, US Geological Survey, Washington, DC.Google Scholar
Batchelor, G. K. 1970 An Introduction to Fluid Dynamics. Cambridge University Press.Google Scholar
Best, J. L. & Reid, I. 1984 Separation zone at open-channel junctions. J. Hydraul. Engng ASCE 110 (11), 1588–1594.Google Scholar
Biron, P. M., Lane, S. N., Roy, A. G., Bradbrook, K. F. & Richards, K. S. 1998 Sensitivity of bed shear stress estimated from vertical velocity profiles: the problem of sampling resolution. Earth Surf. Process. Landf. 23 (2), 133–139.Google Scholar
Biron, P. M., Robson, C., Lapointe, M. F. & Gaskin, S. J. 2004 Comparing different methods of bed shear stress estimates in simple and complex flow fields. Earth Surf. Process. Landf. 29 (11), 1403–1415.Google Scholar
Blanckaert, K. 2009 Saturation of curvature-induced secondary flow, energy losses and turbulence in sharp open-channel bends. Laboratory experiments, analysis and modeling. J. Geophys. Res. 114, F03015.Google Scholar
Blanckaert, K. 2010 Topographic steering, flow recirculation, velocity redistribution and bed topography in sharp meander bends. Water Resour. Res. 46, W09506.Google Scholar
Blanckaert, K. 2011 Hydrodynamic processes in sharply-curved river bends and their morphological implications. J. Geophys. Res. 116, F01003.Google Scholar
Blanckaert, K., Duarte, A., Chen, Q. & Schleiss, A. J. 2012 Flow processes near smooth and rough (concave) outer banks in curved open channels. J. Geophys. Res. 117, F04020.Google Scholar
Blanckaert, K., Kleinhans, M. G., McLelland, S. J., Uijttewaal, W. S. J., Murphy, B. J., van de Kruijs, A., Parsons, D. R. & Chen, Q. 2013 Flow separation at the inner (convex) and outer (concave) banks of constant-width and widening open-channel bends. Earth Surf. Process. Landf. 38, 696–716.Google Scholar
Blanckaert, K. & Lemmin, U. 2006 Means of noise reduction in acoustic turbulence measurements. J. Hydraul Res. IAHR 44 (1), 3–17.Google Scholar
Blanckaert, K. & de Vriend, H. J. 2004 Secondary flow in sharp open-channel bends. J. Fluid Mech. 498, 353–380.Google Scholar
Blanckaert, K. & de Vriend, H. J. 2010 Meander dynamics: a 1D flow model without curvature restrictions. J. Geophys. Res. 115, F04011.Google Scholar
Boyer, C., Roy, A. G. & Best, J. L. 2006 Dynamics of a river channel confluence with discordant beds: Flow turbulence, bed load sediment transport, and bed morphology. J. Geophys. Res. 111, F04007.Google Scholar
Bulle, H. 1926 Untersuchungen über die Geschiebeableitung bei der Spaltung von Wasserläufen. Forsch. Gebiete Ing. 282, 57–84; (in German).Google Scholar
Burge, L. M. & Smith, D. G. 2009 Confined meandering river eddy accretions: sedimentology, channel geometry and depositional processes. In Fluvial Sedimentology VI (ed. Smith, N. D. & Rogers, J.), Special Publication of Internat, Association of Sedimentologists, vol. 28, pp. 113–130. Blackwell Science.Google Scholar
Chow, V. T. 1959 Open Channel Hydraulics. McGraw-Hill.Google Scholar
Constantinescu, G., Kashyap, S., Toyay, T., Rennie, C. D. & Townsend, R. D. 2013 Hydrodynamic processes and sediment erosion mechanisms in an open-channel bend of strong curvature with deformed bathymetry. J. Geophys. Res. 118 (2), 480–496.Google Scholar
Constantinescu, G., Miyawaki, S., Rhoads, B., Sukhodolov, A. & Kirkil, G. 2011 Structure of turbulent flow at a river confluence with momentum and velocity ratios close to 1: insight provided by an eddy resolving numerical simulation. Water Resour. Res. 47, W05507.Google Scholar
Crosato, A.2008 Analysis and modelling of river meandering. PhD thesis, Delft University of Technolgy.Google Scholar
Dargahi, B. 2004 Three-dimensional flow modelling and sediment transport in the River Klaralven. Earth Surf. Process. Landf. 29, 821–852.Google Scholar
De Serres, B., Roy, A. G., Biron, P. M. & Best, J. L. 1999 Three dimensional structure of flow at a confluence of river channels with discordant beds. Geomorphology 26, 313–335.CrossRefGoogle Scholar
Dietrich, W. E. & Whiting, P. 1989 Boundary shear stress and sediment transport in river meanders of sand and gravel. In River Meandering (ed. Ikeda, S. & Parker, G.), Water Resour. Monogr. Ser., vol. 12, pp. 1–50. AGU.Google Scholar
Duarte, A.2008 An experimental study on main flow, secondary flow and turbulence in open-channel bends with emphasis on their interaction with the outer-bank geometry. PhD thesis, no 4227, Ecole Polytechnique Fédérale Lausanne.Google Scholar
Engel, F. L. & Rhoads, B. L. 2012 Interaction among mean flow, turbulence, bed morphology, banks failures and channel planform in an evolving compound meander loop. Geomorphology 163–164, 70–83.Google Scholar
Engelund, F. 1974 Flow and bed topography in channel bends. J. Hydraul. Div. ASCE 100 (HY11), 1631–1648.Google Scholar
Ferguson, R. I., Parsons, D. R., Lane, S. N. & Hardy, R. J. 2003 Flow in meander bends with recirculation at the inner bank. Water Resour. Res. 39 (11), 1322–1333.Google Scholar
Frothingham, K. M. & Rhoads, B. L. 2003 Three-dimensional flow structure and channel change in an asymmetrical compound meander loop, Embarras River, Illinois. Earth Surf. Process. Landf. 28 (6), 625–644.Google Scholar
Hardy, R. J., Lane, S. N. & Yu, D. 2011 Flow structures at an idealized bifurcation: a numerical experiment. Earth Surf. Process. Landf. 36 (15), 2083–2096.Google Scholar
Hickin, E. J. 1974 The development of meanders in natural river-channels. Am. J. Sci. 274 (April), 414–442.Google Scholar
Hinze, J. O. 1975 Turbulence. McGraw-Hill.Google Scholar
Hooke, J. 2003 River meander behaviour and instability: a framework for analyses. Trans. Inst. Brit. Geogr. 28 (2), 238–253.Google Scholar
Hurther, D. & Lemmin, U. 1998 A constant beamwidth transducer for three-dimensional Doppler profile measurements in open channel flow. Meas. Sci. Technol. 9 (10), 1706–1714.Google Scholar
Jamieson, E., Post, G. & Rennie, C. D. 2010 Spatial variability of three dimensional Reynolds stresses in a developing channel bend. Earth Surf. Process. Landf. 35, 1029–1043.Google Scholar
Jin, Y.-C. & Steffler, P. M. 1993 Predicting flow in curved open channels by the depth-averaged method. J. Hydraul. Engng ASCE 119 (1), 109–124.Google Scholar
Kim, S. C., Friedrichs, C. T., Maa, J. P. Y. & Wright, L. D. 2000 Estimating bottom stress in tidal boundary layer from Acoustic Doppler Velocimeter data. J. Hydraul. Engng ASCE 126 (6), 399–406.Google Scholar
Kleinhans, M. G., Ferguson, R. I., Lane, S. N. & Hardy, R. J. 2013 Splitting rivers at theirs seams: bifurcations and avulsion. Earth Surf. Process. Landf. 38, 47–61.Google Scholar
Kleinhans, M. G., Schuurman, F., Bakx, W. & Markies, H. 2009 Meandering channel dynamics in highly cohesive sediment on an intertidal mud flat in the Westerschelde estuary, The Netherlands. Geomorphology 105, 261–276.Google Scholar
Koken, M., Constantinescu, G. & Blanckaert, K. 2013 Hydrodynamic processes, sediment erosion mechanisms, and Reynolds-number-induced scale effects in an open channel bend of strong curvature with flat bathymetry. J. Geophys. Res. 118, 1–17.Google Scholar
Leeder, M. R. & Bridges, P. H. 1975 Flow separation in meander bends. Nature 253 (5490), 338–339.Google Scholar
Leite Ribeiro, M., Blanckaert, K., Roy, A. G. & Schleiss, A. J. 2012 Flow and sediment dynamics in channel confluences. J. Geophys. Res. 117, F01035.Google Scholar
Lemmin, U. & Rolland, T. 1997 Acoustic velocity profiler for laboratory and field studies. J. Hydraul. Engng ASCE 123 (12), 1089–1098.Google Scholar
Markham, A. J. & Thorne, C. R. 1992 Geomorphology of gravel-bed river bends. In Dynamics of Gravel-Bed Rivers (ed. Billi, P., Hey, R. D., Thorne, C. R. & Tacconi, P.), pp. 433–456. Wiley.Google Scholar
Nanson, R. A. 2010 Flow fields in tightly curving meander bends of low width-depth ratio. Earth Surf. Process. Landf. 35 (2), 119–135.Google Scholar
Neary, V. S. & Odgaard, A. J. 1993 3-Dimensional flow structure at open-channel diversions. J. Hydraul. Engng ASCE 119 (11), 1223–1230.Google Scholar
Nelson, J. E.1988 Mechanics of flow and sediment transport over nonuniform erodible beds, PhD dissertation, University of Washington, Seattle, WA, p. 277.Google Scholar
Nezu, I. & Nakagawa, H. 1993 Turbulence in Open-Channel Flows, IAHR-Monograph. Balkema.Google Scholar
Ottevanger, W.2013 Modelling and parameterizing the hydro- and morphodynamics of curved open channels. PhD thesis, Delft University of Technology.Google Scholar
Rhoads, B. L. & Kenworthy, S. T. 1995 Flow structure at an asymmetrical stream confluence. Geomorphology 11 (4), 273–293.Google Scholar
Rhoads, B. L. & Massey, K. 2012 Flow structure and channel change in a sinuous grass-lined stream within an agricultural drainage ditch: implications for ditch stability and aquatic habitat. River Res. Appl. 28 (1), 39–52.Google Scholar
Rhoads, B. L. & Sukhodolov, A. N. 2001 Field investigation of three-dimensional flow structure at stream confluences: 1. Thermal mixing and time-averaged velocities. Water Resour. Res. 37 (9), 2393–2410.Google Scholar
Rozovskii, I. L. 1957 Flow of Water in Bends of Open Channels. Acad. Sci. Ukraine. SSR; Israeli. Progr. Sci. Transl; 1961.Google Scholar
Schnauder, I. & Sukhodolov, A. N. 2012 Flow in a tightly curving meander bend: effects of seasonal changes in aquatic macrophyte cover. Earth Surf. Process. Landf. 37 (11), 1142–1157.Google Scholar
Sime, L. C., Ferguson, R. I. & Church, M. 2007 Estimating shear stress from moving boat acoustic Doppler velocity measurements in a large gravel bed river. Water Resour. Res. 43 (3), W03418.Google Scholar
Simpson, R. L. 1989 Turbulent boundary-layer separation. Annu. Rev. Fluid Mech. 21, 205–234.Google Scholar
Simpson, R. L. 1996 Aspects of turbulent boundary-layer separation. Prog. Aerosp. Sci. 32, 457–521.Google Scholar
Sukhodolov, A. N. 2012 Structure of turbulent flow in a meander bend of a lowland river. Water Resour. Res. 48, W01516.Google Scholar
Sukhodolov, A., Thiele, M. & Bungartz, H. 1998 Turbulence structure in a river reach with sand bed. Water Resour. Res. 34 (5), 1317–1334.Google Scholar
Termini, D. & Piraino, M. 2011 Experimental analysis of cross-sectional flow motion in a large amplitude meandering bend. Earth Surf. Process. Landf. 36, 244–256.Google Scholar
Van Balen, W., Blanckaert, K. & Uijttewaal, W. S. J. 2010 Analysis of the role of turbulence in curved open-channel flow at different water depths by means of experiments, LES and RANS. J. Turbul. 11, Art. No. N 12.Google Scholar
de Vriend, H. J. 1977 A mathematical model of steady flow in curved shallow channels. J. Hydraul. Res. IAHR 15 (1), 37–54.Google Scholar
Wilcock, P. R. 1996 Estimating local bed shear stress from velocity observations. Water Resour. Res. 32 (11), 3361–3366.Google Scholar
Yang, Q. Y., Wang, X. Y., Lu, W. Z. & Wang, X. K. 2009 Experimental study on characteristics of separation zone in confluence zones in rivers. J. Hydrol. Engng 14 (2), 166–171.Google Scholar
Zeng, J., Constantinescu, G., Blanckaert, K. & Weber, L. 2008 Flow and bathymetry in sharp open-channel bends: experiments and predictions. Water Resour. Res. 44, W09401.Google Scholar
Zinger, J., Rhoads, B. L., Best, J. L. & Johnson, K. K. 2014 Flow structure and channel morphodynamics of meander bend chute cutoffs: a case study of the Wabash River, USA. J. Geophys. Res. 118 (4), 2468–2487.Google Scholar