Skip to main content
    • Aa
    • Aa

Impact of height heterogeneity on canopy turbulence

  • A. M. Hamed (a1), M. J. Sadowski (a1), H. M. Nepf (a2) and L. P. Chamorro (a1) (a3) (a4)

The flow development above and within homogeneous and heterogeneous canopies was experimentally studied using particle image velocimetry in a refractive-index-matching channel. The experiments were designed to gain insight into the effect of height heterogeneity on the structure and spatial distribution of the turbulence. The homogeneous model (base case) is constituted of elements of height $h$ arranged in a staggered configuration; whereas the heterogeneous canopy resembled a row canopy and consisted of elements of two heights $h_{1}=h+(1/3)h$ and $h_{2}=h-(1/3)h$ alternated every two rows. Both canopies had the same density, element geometry and mean height. The flow was studied under three submergences $H/h=2$ , 3 and 4, where $H$ denotes the flow depth. The experiments were performed at Reynolds number $Re_{H}\simeq 6500$ , 11 300 and 12 300 and nearly constant Froude number $Fr\simeq 0.1$ . Turbulence statistics complemented with quadrant analysis and proper orthogonal decomposition reveal richer flow dynamics induced by height heterogeneity. Topography-induced spatially periodic mean flows are observed for the heterogeneous canopy. Furthermore, and in contrast to the homogeneous case, non-vanishing vertical velocity is maintained across the entire length of the heterogeneous canopy with increased levels at lower submergence depths. Further alternations were induced in the magnitude and distribution of the turbulent kinetic energy, Reynolds shear stress and characteristics of the canopy mixing layer, evidencing enhanced mixing and turbulent transport for the heterogeneous canopy especially at lower submergence depths. Overall, the results indicate that heterogeneous canopies exhibit greater vertical turbulent exchange at the canopy interface, suggesting a potential for greater scalar exchange and a greater impact on channel hydraulic resistance than a homogeneous canopy of similar roughness density.

Corresponding author
Email address for correspondence:
Hide All
K. Bai  & J. Katz 2014 On the refractive index of sodium iodide solutions for index matching in PIV. Exp. Fluids 55, 16.

K. Bai , J. Katz  & C. Meneveau 2015 Turbulent flow structures inside a canopy with complex multi-scale elements. Boundary-Layer Meteorol. 155 (3), 435457.

E. S. Belcher 2005 Mixing and transport in urban areas. Phil. Trans. R. Soc. Lond. A 363, 29472968.

S. E. Belcher , I. N. Harman  & J. J. Finnigan 2011 The wind in the willows: flows in forest canopies in complex terrain. Annu. Rev. Fluid Mech. 44, 479504.

S. E. Belcher , N. Jerram  & J. C. R. Hunt 2003 Adjustment of a turbulent boundary layer to a canopy of roughness elements. J. Fluid Mech. 488, 369398.

G. Berkooz , P. Holmes  & J. L. Lumley 1993 The proper orthogonal decomposition in the analysis of turbulent flows. Annu. Rev. Fluid Mech. 25 (1), 539575.

A. Chahine , S. Dupont , C. Sinfort  & Y. Brunet 2014 Wind-flow dynamics over a vineyard. Boundary-Layer Meteorol. 151 (3), 557577.

Z. Chen , C. Jiang  & H. M. Nepf 2013 Flow adjustments at the leading edge of a submerged quatic canopy. Water Resour. Res. 49, 55375551.

O. Coceal  & S. E. Belcher 2004 A canopy model of mean winds through urban areas. Q. J. R. Meteorol. Soc. 130, 13491372.

W. C. Dennison , R. J. Orth , K. A. Moore , J. C. Stevenson , V. Carter , S. Kollar , P. W. Bergstorm  & R. A. Batiuk 1993 Assessing water quality with submersed aquatic vegetation. BioScience 43 (2), 8694.

J. T. Dijkstra  & R. E. Uittenbogaard 2010 Modeling the interaction between flow and highly flexible aquatic vegetation. Water Resour. Res. 46 (12), W12547.

J. Finnigan 2000 Turbulence in plant canopies. Annu. Rev. Fluid Mech. 32 (1), 519571.

M. S. Fonseca  & J. A. Cahalan 1992 A preliminary evaluation of wave attenuation by four species of seagrass. Estuar. Coast. Shelf Sci. 35, 565576.

M. Ghisalberti 2009 Obstructed shear flows: similarities across systems and scales. J. Fluid Mech. 641, 5161.

A. M. Hamed , A. Kamdar , L. Castillo  & L. P. Chamorro 2015 Turbulent boundary layer over 2D and 3D large scale wavy walls. Phys. Fluids 27, 106601.

C. P. Hawkins , M. L. Murphy , N. H. Anderson  & M. A. Wilzbach 1983 Density of fish and salamanders in relation to riparian canopy and physical habitat in streams of the northwestern United States. Can. J. Fish. Aquat. Sci. 40.

J. L. Heilman , K. J. McInnes , M. J. Savage , R. W. Gesch  & R. J. Lascano 1994 Soil and canopy energy balances in a west Texas vineyard. Agric. Forest Meteorol. 71 (1–2), 99114.

C. Lai , G. Katul , R. Oren , D. Ellsworth  & K. Schäfer 2000 Modeling CO2 and water vapor turbulent flux distributions within a forest canopy. J. Geophys. Res. Atmos. 105 (D21), 2633326351.

S. S. Lu  & W. W. Willmarth 1973 Measurements of the structure of the Reynolds stress in a turbulent boundary layer. J. Fluid Mech. 60 (03), 481511.

M. Luhar  & H. M. Nepf 2011 Flow-induced reconfiguration of buoyant and flexible aquatic vegetation. Limnol. Oceanogr. 56 (6), 20032017.

M. Luhar  & H. M. Nepf 2013 From the blade scale to the reach scale: a characterization of aquatic vegetative drag. Adv. Water Resour. 51, 305316.

A. P. Morse , B. A. Gardiner  & B. J. Marshall 2002 Mechanisms controlling turbulence development across a forest edge. Boundary-Layer Meteorol. 103 (2), 227251.

H. M. Nepf 2012 Flow and transport in regions with aquatic vegetation. Annu. Rev. Fluid Mech. 44, 123142.

H. M. Nepf  & E. R. Vivoni 2000 Flow structure in depth-limited, vegetated flow. J. Geophys. Res. Oceans 105 (C12), 2854728557.

I. Nezu  & M. Sanjou 2008 Turbulent structure and coherent motion in vegetated canopy open-channel flows. J. Hydro Environ. Res. 2, 6290.

D. Poggi , A. Porporato , L. Ridolfi , J. D. Albertson  & G. G. Katul 2004 The effect of vegetation density on canopy sub-layer turbulence. Boundary-Layer Meteorol. 111 (3), 565587.

M. R. Raupach , J. J. Finnigan  & Y. Brunet 1996 Coherent eddies and turbulence in vegetation canopies: the mixing-layer analogy. Boundary-Layer Meteorol. 78 (3–4), 351382.

M. R. Raupach  & A. S. Thom 1981 Turbulence in and above plant canopies. Annu. Rev. Fluid Mech. 13 (1), 97129.

J. T. Rominger  & H. M. Nepf 2011 Flow adjustment and interior flow associated with a rectangule porous obstruction. J. Fluid Mech. 680, 636659.

L. Sirovich 1987 Turbulence and the dynamics of coherent structures. Part I: coherent structures. Q. Appl. Maths 45 (3), 561571.

C. Souch  & S. Grimmond 2006 Applied climatology: urban climate. Prog. Phys. Geog. 30 (2), 270.

Y. Tanino  & H. M. Nepf 2008 Laboratory investigation of mean drag in a random array of rigid, emergent cylinders. J. Hydraul. Engng ASCE 134, 3441.

A. Weiss  & L. H. Allen 1976 Air-flow patterns in vineyard rows. Agric. Meteorol. 16 (3), 329342.

B. L. White  & H. M. Nepf 2007 Shear instability and coherent structures in shallow flow adjacent to a porous layer. J. Fluid Mech. 593, 132.

W. Zhu , R. van Hout  & J. Katz 2007 On the flow structure and turbulence during sweep and ejection events in a wind-tunnel model canopy. Boundary-Layer Meteorol. 124 (2), 205233.

Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
  • URL: /core/journals/journal-of-fluid-mechanics
Please enter your name
Please enter a valid email address
Who would you like to send this to? *



Full text views

Total number of HTML views: 17
Total number of PDF views: 206 *
Loading metrics...

Abstract views

Total abstract views: 470 *
Loading metrics...

* Views captured on Cambridge Core between 27th January 2017 - 18th October 2017. This data will be updated every 24 hours.