Spatial Variability of the Flow and Turbulence Within a Model Canopy

Harman, Ian N.; Böhm, Margi; Finnigan, John; Hughes, Dale

doi:10.1007/s10546-016-0150-0

Cited by 18 publications

(16 citation statements)

References 52 publications

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“…This parameter restricts the use of 3D-PTV in turbulent flows with a significant mean flow to very high-speed imaging and short recording times. However, inhomogeneous canopy flows require long measurement durations for the statistics to be convergent and independent; typical wind tunnel experiments 3,9,12,14,15 use minutes of recording times at each point of interest, resulting in combined sampling periods on the order of hours.…”

Section: Introductionmentioning

confidence: 99%

Extended 3D-PTV for direct measurements of Lagrangian statistics of canopy turbulence in a wind tunnel

Shnapp

Shapira²,

Peri

et al. 2019

Sci Rep

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Direct estimation of Lagrangian turbulence statistics is essential for the proper modeling of dispersion and transport in highly obstructed canopy flows. However, Lagrangian flow measurements demand very high rates of data acquisition, resulting in bottlenecks that prevented the estimation of Lagrangian statistics in canopy flows hitherto. We report on a new extension to the 3D Particle Tracking Velocimetry (3D-PTV) method, featuring real-time particle segmentation that outputs centroids and sizes of tracer particles and performed on dedicated hardware during high-speed digital video acquisition from multiple cameras. The proposed extension results in four orders of magnitude reduction in data transfer rate that enables to perform substantially longer experimental runs, facilitating measurements of convergent statistics. The extended method is demonstrated through an experimental wind tunnel investigation of the Lagrangian statistics in a heterogeneous canopy flow. We observe that acceleration statistics are affected by the mean shear at the top of the canopy layer and that Lagrangian particle dispersion at small scales is dominated by turbulence in the wake of the roughness elements. This approach enables to overcome major shortcomings from Eulerian-based measurements which rely on assumptions such as the Taylor’s frozen turbulence hypothesis, which is known to fail in highly turbulent flows.

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Section: Introductionmentioning

confidence: 99%

Extended 3D-PTV for direct measurements of Lagrangian statistics of canopy turbulence in a wind tunnel

Shnapp

Shapira²,

Peri

et al. 2019

Sci Rep

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“…In heterogeneous forested terrain, full-scale field experiments have been made near forest edges (Raynor, 1971;Irvine et al, 1997;Dellwik et al, 2014), and larger scale experiments in heterogeneous forested terrain are currently carried out (Mann et al, 2017). However, much of our knowledge on wind flows over and in forests relies on wind tunnel studies using single-scale tree models like cylinders (Seginer et al, 1976;Poggi et al, 2004;Zhu et al, 2006;Segalini et al, 2013), strips (Raupach et al, 1986;Harman et al, 2016) or flexible stalks (Stacey et al, 1994). Also real trees have previously been put into wind tunnels (Vollsinger et al, 2005, e.g.,][), however, with the focus of studying the effect of wind on the tree, rather than the effect of the tree on the wind.…”

Section: Introductionmentioning

confidence: 99%

Observed and modeled near-wake flow behind a solitary tree

Dellwik

Laan

Angelou

et al. 2019

Agricultural and Forest Meteorology

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“…An observation that is unique to the coral H / h c > 1 cases is the increase of the integral scales in the lower part of the wake zone, showing a peak around z / h c ~0.2. Such a peak was not reported in other canopy flows (e.g., Shaw et al, , also cited by Finnigan, ; Harman et al, ; and Duman, ). A common explanation would be the effect of the larger void space found in the lower part of the coral canopy on the eddy formation.…”

Section: Resultsmentioning

confidence: 89%

“…As the velocity must reach zero at the bed, a second inflection point must exist in that region. With that in mind, while the mean velocity profiles at the canopy interface ( z / h c ~1) rapidly converge to a single uniform curve which universally demonstrates an inflection point, the velocity profiles are highly variable in space within the canopy (see Harman et al, , for a demonstration of the spatial variations in the velocity profiles). Therefore, the existence and the location of an inflection point in the wake zone will strongly depend on the location of the vertical profile within the horizontal plane.…”

Section: Resultsmentioning

confidence: 99%

The Effect of Water Depth and Internal Geometry on the Turbulent Flow Inside a Coral Reef

Asher

Shavit

2019

JGR Oceans

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The flow of water through coral reefs controls the transport of mass, momentum, and energy and, as a result, affects key processes such as feeding, photosynthesis, and reproduction. While it is often analyzed as a typical canopy flow, the flow through coral reefs is different from both terrestrial and aquatic canopies. A combination of a nonuniform vertical distribution of porosity and resistance and variations in relative submergence generates regions of high‐velocity gradients, increased integral length scales and instabilities which have not previously been quantified in detail. Here we report on velocity measurements inside and above a laboratory reef made of 81 Pocillopora Meandrina skeletons, for a range of relative submergence and flow rates. Under the action of a pressure gradient, the mean velocity shows an increase in the wake zone, generating a potential source for mixing due to a second inflection point. Unlike classical boundary layers and other canopy flows, a quadrant analysis shows that the number of inward/outward interactions events is larger than sweeps/ejections inside the canopy wake zone, due to the sign change in the mean velocity gradient. The vertical distribution of the integral length scales shows a local maximum in the lower part of the wake zone. Finally, under fully submerged conditions, the stream‐wise turbulent energy spectra inside the reef follow an approximate kx−7/3, as opposed to the expected kx−5/3 behavior above the reef. Under near‐emergent conditions, no fit to such a power law could be obtained.

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Spatial Variability of the Flow and Turbulence Within a Model Canopy

Cited by 18 publications

References 52 publications

Extended 3D-PTV for direct measurements of Lagrangian statistics of canopy turbulence in a wind tunnel

Extended 3D-PTV for direct measurements of Lagrangian statistics of canopy turbulence in a wind tunnel

Observed and modeled near-wake flow behind a solitary tree

The Effect of Water Depth and Internal Geometry on the Turbulent Flow Inside a Coral Reef

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