Flow analysis in a channel with flexible vegetation using double-averaging method

• Autorzy: Righetti M.
• Języki publikacji: EN

Abstrakty

EN

The paper addresses the problem of the resistance due to vegetation in an open channel flow, characterized by partially and fully submerged vegetation formed by colonies of bushes. The flow is characterized by significant spatial variations of velocity between vertical profiles that make the traditional approach based on time averaging of turbulent fluctuations inconvenient. A more useful procedure, based on time and spatial averaging (Double-Averaging Method) is applied for the flow field analysis and characterization. The vertical distribution of mean velocity and turbulent stresses at different spatial locations has been measured with a 3D Acoustic Doppler Velocimeter (ADV) for two different vegetation densities where fully submerged real bushes (salix pentandra) have been used. Velocity measurements were completed together with the measurements of drag exerted on the flow by bushes at different flow depths. The analysis of velocity measurements allows depicting the fundamental characteristics of both the mean flow field and turbulence. The experimental data show that the contribution of form-induced stresses to the momentum balance cannot be neglected. The mean velocity profiles and the spatially averaged turbulent intensity profiles allow inferring that the vegetation density is a driving parameter for the development of a mixing layer at the canopy top in the case of submerged vegetation. Moreover, the net upward turbulent momentum flux, evaluated with the methodology proposed by Lu and Willmarth (1973), appears to be damped for increased vegetation density; this finding can rationally explain the reduction of the suspended sediment transport capacity typically observed in free surface flows over a vegetated bed.

Słowa kluczowe

EN

vegetated channels; turbulence; Double-Averaging Method

• Wydawca: Instytut Geofizyki PAN ; Springer
• Czasopismo: Acta Geophysica
• Rocznik: 2008
• Tom: Vol. 56, no. 3
• Strony: 801--823
• Opis fizyczny: bibliogr. 37 poz.

Twórcy

autor

Righetti M.

• Department of Civil and Environmental Engineering, University of Trento, Trento, Italy,

Bibliografia

• Armanini, A., M. Righetti, and P. Grisenti (2005), Direct measurements of vegetation resistance in prototipe scale, J. Hydraul. Res. 43, 5, 481-487.
• Carollo, F.G., V. Ferro, and D. Termini (2002), Flow velocity measurements in vegetated channels, J. Hydraul. Eng. ASCE 127, 7, 664-673.
• Christensen, B.A. (1985), Open channel and sheet flow over flexible roughness, Proceedings of the 21st IAHR Congress in Melbourne, Australia, 462-467.
• Fathi-Maghadam, M., and N. Kouwen (1997), Nonrigid, nonsubmerged, vegetative roughness on floodplains, J. Hydraul. Eng. ASCE 123, 1, 51-57.
• Finnigan, J. (2000), Turbulence in plant canopies, Ann. Rev. Fluid Mech. 32, 519-571.
• Freeman, G.E., W. Rahmeyer, and R.R. Copeland (2000), Determination of resistance due to shrubs and woody vegetation, Technical Report TA7 E8, Stock Number AD A383 997 DTIC, U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS.
• Ghisalberti, M., and H. Nepf (2002), Mixing layers and coherent structures in vegetated aquatic flow, J. Geophys. Res. 107, C2, 1-11.
• Ghisalberti, M., and H. Nepf (2004), The limited growth of vegetated shear-layers, Water Resour. Res. 40, W07502, DOI: 10.1029/2003WR002776.
• Ghisalberti, M., and H. Nepf (2005), Mass transfer in vegetated shear flows, Environ. Fluid Mech. 5, 6, 527-551, DOI: 10.1007/s10652-005-0419-1.
• Ikeda, S., and M. Kanazawa (1996), Three-dimensional organized vortices above flexible water plants, J. Hydraul. Eng. ASCE 122, 634-640.
• Jarvela, J. (2002), Flow resistance of flexible and stiff vegetation: a flume study with natural plants, J. Hydrol. 269, 44-54(11).
• Kaftori, D., G. Hetsroni, and S. Banerjee (1995), Particle behavior in the turbulent boundary layer: I. Motion, deposition and entrainment, Phys. Fluids 7, 5, 1095-1106.
• Katul, G.G., P. Wiberg, J.D. Albertson, and G.W. Hornberger (2002), A mixing layer theory for flow resistance in shallow streams, Water Resour. Res. 38, 11, art. no. 1250.
• Klopstra, D., J.M. Barneveld, and E.H. van Noortwijk (1997), Analytical model for hydraulic roughness of submerged vegetation. Managing water: Coping with scarcity and adbundance, Proceedings of XXVII AIHR Conference, San Francisco, CA USA, August 1997.
• Kouwen, N., T.E. Unny, and H.M. Hill (1969), Flow retardance in vegetated channels, J. Irrigation and Drainage Division ASCE, 95, IR2, 329-342.
• Lindner, K. (1982), Der Strömungswiderstand von Pflanzenbeständen, Mitteilungen Leichtweiss-Institut für Wasserbau, TU Braunschweig, Heft 75.
• Lopez, F., and M.H. García (2001), Open-channel flow through simulated vegetation: mean flow and turbulence modeling, J. Hydraul. Eng. 127, 392-402.
• Lu, S.S., and W.W. Willmarth (1973), Measurement of structure of the Reynolds stress in a turbulent boundary layer, J. Fluid Mech. 60, 481-511.
• Ming, R.H., and H.W. Shen (1973), Effect of tall vegetations on flow and sediment, J. Hydraul. Res. ASCE 99, HY5, 793-814.
• Nepf, H.M. (1999), Drag, turbulence and diffusion in flow through emergent vegetation, Water Resour. Res. 35, 479-489.
• Nepf, H.M., and E.R. Vivoni (1999), Turbulence structure in depth-limited vegetated flows: Transition between emergent and submerged regimes, Proceedings of the XXVIII AIHR Conference, Graz, Austria, September 1999.
• Nikora, V., D. Goring, I. McEwan, and G. Griffiths (2001), Spatially averaged open-channel flow over rough bed, J. Hydraul. Eng. ASCE 127, 2, 123-133.
• Nikora, V., K. Koll, I. McEwan, S. McLean, and A. Dittrich (2004), Velocity distribution in the roughness layer of rough-bed flows, J. Hydraul. Eng. ASCE 130, 10, 1036-1042.
• Nobile, I. (2007), Dendrometric analysis of riparian vegetation in mountain streams (in Italian), Ph.D. Thesis, University of Trento, Italy.
• Oplatka, M. (1998), Stabilität von Weidenverbauungen an Flussufern, Mitteilungen der Versuchsnastalt für Wasserbau, Hydrologie und Glaziologie 156.
• Pasche, E., and G. Rouvé (1985), Overbank flow with vegetatively roughened flood plains, J. Hydraul. Eng. 111, 9, 1262-1278.
• Petryk, S., and G. Bosmajian III (1975), Analysis of flow through vegetation, J. Hydraul. Div. ASCE 101, HY7, 871-884.
• Poggi, D., A. Porporato, L. Ridolfi, J.D. Albertson, and G.G. Katul (2004), The effect of vegetation density on canopy sub-layer turbulence, Bound.-Layer Meteor. 111, 565-587.
• Pokrajac, D., McEwan, and Nikora, V. (2008), Spatially averaged turbulent stress and its partitioning, Experiments in Fluids, DOI: 10.1007/s00348-008-0463-y.
• Raupach, M.R., and R.H. Shaw (1982), Averaging procedures for flow within vegetation canopies, Bound.-Layer Meteor. 22, 79-90.
• Raupach, M.R., J.J. Finnigan, and Y. Brunet (1996), Coherent eddies and turbulence in vegetation canopies: The mixing layer analogy, Bound.-Layer Meteor. 78, 351-382.
• Righetti, M., and A. Armanini (2002), Flow resistance in open channel flows with sparsely distributed bushes, J. Hydrol. 269, 55-64.
• Righetti, M., and G.P. Romano (2004), Particle-fluid interactions in a plane nearwall turbulent flow, J. Fluid Mech. 505, 93-121.
• Rogers, M.M., and R.D. Moser (1994), Direct simulation of a self-similar turbulent mixing layer, Phys. Fluids A, 6, 2, 903-923.
• Stephan, U., and D. Gutknecht (2002), Hydraulic resistance of submerged flexible vegetation, J. Hydrol. 269, 27-43.
• Sumer, M.B., and R. Deigaard (1981), Lift forces on moving particles near boundaries, Part 2, J. Fluid Mech. 109, 311-337.
• Wilson, N.R., and R.H. Shaw (1977), A higher order closure model for canopy flow, J. Appl. Meteorol. 16, 1197-1205.