Abstract
Floating vegetation island (FVI) provides an effective way to remove excessive nutrition and pollutants in rivers. The Reynolds stress model (RSM) is employed to investigate the hydrodynamic characteristics induced by varied canopy densities of FVI in an open channel. In longitudinal direction, four regions are subdivided according to the flow development process: upstream adjustment region (LUD), diverging flow region (LDF), shear layer growth region (LSD), and fully developed region. The increasing canopy density accelerates the flow adjustment in the diverging flow region and shear layer growth region, signaling a shorter distance to reach an equilibrium stage, while LUD keeps a constant. The vertical profiles of the normalized velocity are found to be self-similar downstream of the diverging flow region. In the vertical direction, the streamwise velocity profiles in the mixing layer collapse for all densities and obey the hyperbolic tangent law. Normalized penetration depth into the canopy was fitted as a function of dimensionless canopy density given by δc / hc = 0.404(CDahc)−0.316. This finding indicates a large space for rapid water renewal between the canopy region and the underlying water driven by the shear-scale vortices. In the lateral direction, the intensification of secondary current and the increasing number of secondary current cells with increasing canopy density reveal that dense floating canopies contribute to strong momentum exchange. The centers of vortices move as canopy density increases, while the vortices in canopy region do not merge with those in the gap region, as limited by the height and width of the canopy region. The distribution of longitudinal velocity in the transects is significantly influenced by secondary current.
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References
Headley T. R., Tanner C. C. Application of floating wetlands for enhanced stormwater treatment: A review [C]. NIWA Client Report: HAM, Hamilton, New Zealand, 2006.
Zhao M. D., Fan Z. L. Emergent vegetation flow with varying vertical porosity [J]. Journal of Hydrodynamics, 2019, 31(5): 1043–1051.
Yang Z. H., Bai F. P., Huai W. X. Lattice Boltzmann method for simulating flows in open-channel with partial emergent rigid vegetation cover [J]. Journal of Hydrodynamics, 2019, 31(4): 717–724.
Tanner C. C., Headley T. R. Components of floating emergent macrophyte treatment wetlands influencing removal of stormwater pollutants [J]. Ecological Engineering, 2011, 37(3): 474–486.
Murray-Gulde C. L., Huddleston G. M., Garber K. V. et al. Contributions of schoenoplectus californicus in a constructed wetland system receiving copper contaminated wastewater [J]. Water, Air, and Soil Pollution, 2005, 163(1): 355–378.
Neori A., Reddy K., Čížková-Končalová H. et al. Bioactive chemicals and biological-biochemical activities and their functions in rhizospheres of wetland plants [J]. The Botanical Review, 2000, 66: 350–378.
Belcher S. E., Jerram N., Hunt J. C. R. Adjustment of a turbulent boundary layer to a canopy of roughness elements [J]. Journal of Fluid Mechanics, 2003, 488: 369–398.
Rominger J. T., Nepf H. M. Flow adjustment and interior flow associated with a rectangular porous obstruction [J]. Journal of Fluid Mechanics, 2011, 680: 636–659.
Nepf H., Ghisalberti M., White B. et al. Retention time and dispersion associated with submerged aquatic canopies [J]. Water Resources Research, 2007, 43(4): W04422.
Ghisalberti M., Nepf H. M. Mixing layers and coherent structures in vegetated aquatic flows [J]. Journal of Geophysical Research-Oceans, 2002, 107(2): 1–11.
Plew D. R. Depth-averaged drag coefficient for modeling flow through suspended canopies [J]. Journal of Hydraulic Engineering, ASCE, 2011, 137(2): 234–247.
Zhao F., Huai W. X., Li D. Numerical modeling of open channel flow with suspended canopy [J]. Advances in Water Resources, 2017, 105: 132–143.
Okamoto T., Nezu I. Spatial evolution of coherent motions in finite-length vegetation patch flow [J]. Environmental Fluid Mechanics, 2013, 13(5): 417–434.
Huai W. X., Xue W. Y., Qian Z. D. Large-eddy simulation of turbulent rectangular open-channel flow with an emergent rigid vegetation patch [J]. Advances in Water Resources, 2015, 80: 30–42.
Yu W. Y., Jiang C. B., Shi Y. et al. Experimental study of the impact of the floating-vegetation island on mean and turbulence structure [J]. Journal of Hydrodynamics, 2019, 31(5): 922–930.
White B. L., Nepf H. M. Shear instability and coherent structures in shallow flow adjacent to a porous layer [J]. Journal of Fluid Mechanics, 2007, 593: 1–32.
Huai W. X., Zhang J., Katul G. G. et al. The structure of turbulent flow through submerged flexible vegetation [J]. Journal of Hydrodynamics, 2019, 31(2): 274–292.
Dupuis V., Proust S., Berni C. et al. Mixing layer development in compound channel flows with submerged and emergent rigid vegetation over the floodplains [J]. Experiments in Fluids, 2017, 58(4): 30.
Proust S., Fernandes J. N., Peltier Y. et al. Turbulent nonuniform flows in straight compound open-channels [J]. Journal of Hydraulic Research, 2013, 51(6): 656–667.
Choi S., Kang H. Characteristics of mean flow and turbulence statistics of depth-limited flows with submerged vegetation in a rectangular open-channel [J]. Journal of Hydraulic Research, 2016, 54(5): 527–540.
Choi S., Kang H. Numerical investigations of mean flow and turbulence structures of partly-vegetated open-channel flows using the Reynolds stress model [J]. Journal of Hydraulic Research, 2010, 44(2): 203–217.
Sonnenwald F., Guymer I., Stovin V. A CFD-based mixing model for vegetated flows [J]. Water Resources Research, 2019, 55(3): 2322–2347.
King A. T., Tinoco R. O., Cowen E. A. A k - ε turbulence model based on the scales of vertical shear and stem wakes valid for emergent and submerged vegetated flows [J]. Journal of Fluid Mechanics, 2012, 701: 1–39.
Cheng W. W., Sun Z. C., Liang S. X. Numerical simulation of flow through suspended and submerged canopy [J]. Advances in Water Resources, 2019, 127: 109–119.
Lien F. S., Leschziner M. A. Assessment of turbulence-transport models including non-linear RNG eddy-viscosity formulation and second-moment closure for flow over a backward-facing step [J]. Computers and Fluids, 1994, 23(8): 983–1004.
Launder B. E. Second-moment closure and its use in modelling turbulent industrial flows [J]. International Journal for Numerical Methods in Fluids, 1989, 9(8): 963–985.
Launder B. E. Second-moment closure: present … and future? [J]. International Journal of Heat and Fluid Flow, 1989, 10(4): 282–300.
Gibson M. M., Launder B. E. Ground effects on pressure fluctuations in the atmospheric boundary layer [J]. Journal of Fluid Mechanics, 1978, 86(3): 491–511.
Fu S., Launder B. E., Leschziner M. A. Modelling strongly swirling recirculating jet flow with Reynolds-stress transport closures [C]. 6th Symposium on Turbulent Shear Flows, Toulouse, France, 1987.
Choi S., Kang H. Numerical investigations of mean flow and turbulence structures of partly-vegetated open-channel flows using the Reynolds stress model [J]. Journal of Hydraulic Research, 2006, 44(2): 203–217.
Choi S., Kang H. Reynolds stress modeling of vegetated open-channel flows [J]. Journal of Hydraulic Research, 2004, 42(1): 3–11.
Lopez F., Garcia M. H. Mean flow and turbulence structure of open-channel flow through non-emergent vegetation [J]. Journal of Hydraulic Engineering, ASCE, 2001, 127(5): 392–402.
Kim H. S., Kimura I., Park M. Numerical simulation of flow and suspended sediment deposition within and around a circular patch of vegetation on a rigid bed [J]. Water Resources Research, 2018, 54(10): 7231–7251.
Dimitris S., Panayotis P. Effect of a vegetation patch on turbulent channel flow [J]. Journal of Hydraulic Research, 2011, 49(2): 157–167.
Dimitris S., Panayotis P. Macroscopic turbulence models and their application in turbulent vegetated flows [J]. Journal of Hydraulic Engineering, 2011, 137(3): 315–332.
Liu Z. W., Chen Y. C., Wu Y. Y. et al. Simulation of exchange flow between open water and floating vegetation using a modified RNG k — ε turbulence model [J]. Environmental Fluid Mechanics, 2017, 17(2): 355–372.
Brito M., Fernandes J., Leal J. B. Porous media approach for rans simulation of compound open-channel flows with submerged vegetated floodplains [J]. Environmental Fluid Mechanics, 2016, 16(6): 1247–1266.
Koftis T., Prinos P. Reynolds stress modelling of flow in compound channels with vegetated floodplains [J]. Journal of Applied Water Engineering and Research, 2018, 6(1): 17–27.
Morse A. P., Gardiner B. A., Marshall B. J. Mechanisms controlling turbulence development across a forest edge [J]. Boundary-Layer Meteorology, 2002, 103(2): 227–251.
Chen Z. B., Jiang C. B., Nepf H. Flow adjustment at the leading edge of a submerged aquatic canopy [J]. Water Resources Research, 2013, 49(9): 5537–5551.
Yang B., Raupach M. R., Shaw R. H. et al. Large-eddy simulation of turbulent flow across a forest edge. Part I: Flow statistics [J]. Boundary-Layer Meteorology, 2006, 120(3): 377–412.
Zong L. J., Nepf H. Flow and deposition in and around a finite patch of vegetation [J]. Geomorphology, 2010, 116(3–4): 363–372.
Tseung H. L., Kikkert G. A., Plew D. Hydrodynamics of suspended canopies with limited length and width [J]. Environmental Fluid Mechanics, 2016, 16(1): 145–166
Li W. Q., Wang D., Jiao J. L. et al. Effects of vegetation patch density on flow velocity characteristics inan open channel [J]. Journal of Hydrodynamics, 2019, 31(5): 1052–1059.
Coceal O., Belcher S. E. A canopy model of mean winds through urban areas [J]. Quarterly Journal of the Royal Meteorological Society, 2004, 130(599): 1349–1372.
Raupach M. R., Finnigan J. J., Brunei Y. Coherent eddies and turbulence in vegetation canopies: the mixing-layer analogy [J]. Boundary-Layer Meteorology, 1996, 78(3): 351–382.
Nepf H. M. Hydrodynamics of vegetated channels [J]. Journal of Hydraulic Research, 2012, 50(3): 262–279.
Yule A. Two-dimensional self-preserving turbulent mixing layers at different free stream velocity ratios [R]. London, UK: HM stationary Office, 1972.
Ho C. M., Huerre P. Perturbed free shear layers [J]. Annual Review of Fluid Mechanics, 1984, 16(1): 365–422.
Winant C. D., Browand F. K. Vortex pairing: The mechanism of turbulent mixing-layer growth at moderate Reynolds number [J]. Journal of Fluid Mechanics, 1974, 63: 237–255.
Ghisalberti M., Nepf H. M. The limited growth of vegetated shear layers [J]. Water Resources Research, 2004, 40(7): W07502.
Yan C., Nepf H. M., Huang W. X. et al. Large eddy simulation of flow and scalar transport in a vegetated channel [J]. Environmental Fluid Mechanics, 2017, 17(3): 497–519.
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Biography: Yi-dan Ai (1998-), Female, Ph. D. Candidate
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Ai, Yd., Liu, My. & Huai, Wx. Numerical investigation of flow with floating vegetation island. J Hydrodyn 32, 31–43 (2020). https://doi.org/10.1007/s42241-020-0004-6
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DOI: https://doi.org/10.1007/s42241-020-0004-6