Measurements of pollen grain dispersal in still air and stationary, near homogeneous, isotropic turbulence

Sabban, Lilach; Hout, R. van

doi:10.1016/j.jaerosci.2011.08.001

Cited by 45 publications

(38 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Natural processes include pollen and seed dispersion in the atmosphere, Sabban and van Hout [15]; whereas industrial processes include pharmaceutical processing, Erni et al [6] and the emission of contaminants from combustion processes as in Moffet and Prather [14].…”

Section: Introductionmentioning

confidence: 99%

Edge effects on the fluttering characteristics of freely falling planar particles

2018

View full text Add to dashboard Cite

The effect of particle edge geometry on the descent motion of free falling planar particles is examined through experiments. Various planar particles, such as disk and polygons, with identical frontal areas (A p ) and different number of edges (or perimeter) are used. All particles are designed such that their values of Galileo number (G) and dimensionless moment of inertia (I * ) correspond to the previously identified fluttering regime of particle motion. Several modes of secondary motion are observed for the same particle and conditions, and these are not equally probable. This probability depends on the particle shape. Disks and heptagons were found to prefer a 'planar zig-zag' behaviour. These planar motions are composed of gliding sweeps and turning sections. As the number of sides in the polygon decreases, i.e. for hexagons and pentagons, the trajectory transition to a more three-dimensional form. These trajectories were found to be restricted to one plane per swing but the subsequent swings are in other planes. Further decrease in number of sides to a square results in the trajectories having a severe out-of-plane motion. These sub-regimes of particle motion within the fluttering regime are consistent with those reported for disks in previous studies.Based on this information, a new length scale that accounts for the frontal area of the particles and its edge geometry (i.e. perimeter) is proposed. This length scale represents the first approach to determine an equivalent disks for planar particles such that the phase digram in the Reynolds number (Re) -dimensionless moment of inertia (I * ) domain can be used to characterise the motion of planar particles with different frontal geometries. However further experiments covering other domains of the regime map are needed to verify its universality. *

show abstract

Section: Introductionmentioning

confidence: 99%

Edge effects on the fluttering characteristics of freely falling planar particles

2018

View full text Add to dashboard Cite

show abstract

“…The flow field in the wake of the spike was measured using Particle Image Velocimetry (PIV; e.g., Raffel et al 2007) and pollen released by the anthers was tracked using high speed, digital inline holographic cinematography (e.g., Sabban and van Hout 2011). In the following, both setups will be discussed in detail.…”

Section: Methodsmentioning

confidence: 99%

“…We used hologram reconstruction software (FFT based) developed by Sheng et al (2006) which allowed fast processing. Particle tracking in successive time steps was done using in‐house developed MATLAB ® based software (Sabban and van Hout 2011) consisting of the following main steps. First, noise and spatial non‐uniformities were reduced by background subtraction (Fig.…”

Section: Methodsmentioning

confidence: 99%

“…Subsequently, assuming Stokes flow for which Re c = | U r | d c /ν << 1, and U r is the relative velocity vector between clump and air, the clump still air settling velocity is given by: V c = ( N c 2 η) 1/3 V s (Martin et al 2009). Here, the measured still air settling velocity of a single ragweed pollen is, V s ≈ −1.40 cm/s (Durham 1946, Sabban and van Hout 2011). Note that the here applied procedure differs from Martin et al (2009) who based their hypothetical spherical clump on the diameter of the largest inscribed circle inside a pollen clump silhouette.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Measurement of pollen clump release and breakup in the vicinity of ragweed (A. confertiflora) staminate flowers

Sabban¹,

Jacobson²,

Hout³

2012

Ecosphere

Self Cite

View full text Add to dashboard Cite

Pollen dispersal is fundamental in a plant's reproductive ecology and as a result of fragmentation of the landscape, questions have been raised on how isolated plant populations can still exchange genetic information. A common mechanism for gene exchange is wind pollination (anemophily). A successful anemophilous species native to North America is ragweed (Ambrosia), a weed that is hard to eradicate after it takes root on crop fields and its pollen causes very strong allergenic effects (hay fever). Despite the extremely clumpy nature of ragweed pollen that should limit its long distance dispersal, ragweed has spread rapidly across the world during the last century while maintaining a high genetic diversity. One of the reasons for its success may be prolific pollen production as well as an efficient pollen clump release and breakup mechanism. Efficient pollen entrainment and dispersal into the atmosphere is highly influenced by flow field characteristics as pollen released into the atmosphere initially encounters flow structures created by the plant's morphology. Here, the flow field in the wake of a mature ragweed spike having multiple staminate flowers as well as pollen release was studied using Particle Image Velocimetry and high‐speed, inline holographic cinematography. The latter enabled to track the pollen in a 3D volume. The spike was set up in a wind tunnel and exposed to wind speeds ranging from 1 to 2 m/s. Results indicated that ragweed pollen was released in multiple sized clumps containing tens to several thousand single grains. Clumps were both “pulled apart” at the point of entrainment while exiting the flowers as well as broke up in smaller sized clumps in high shear rate flow regions not far from the spike. In addition, the largest clumps that did not travel far, deposited in the vicinity of the spike, breaking apart into many small clumps upon deposition. Based on our results, initial release and dispersal of ragweed pollen clumps is characterized by three concomitant mechanisms of clump breakup occurring at entrainment, in mid‐air and on deposition, which make it perfectly suited to disperse pollen over a wide range of spatial scales.

show abstract

“…C Turbulent dispersion of passive scalar quantities, like temperature and concentration, has been intensely studied because of the numerous environmental and industrial applications. [1][2][3][4] Large-scale studies focusing on dispersion in atmospheric flow conditions are often conducted in the field, where features such as surface roughness and vertical gradients in temperature and wind speed complicate the flow and corresponding interpretation. [5][6][7] Many dispersion studies have also been performed in more controlled laboratory settings, especially in wind tunnels where the degree of turbulence can be carefully fine-tuned using different control devices: honeycombs straighten the flow and reduce the fan swirl, fine mesh screens suppress the free stream turbulence, and contractions accelerate the flow and make it more isotropic.…”

mentioning

confidence: 99%

Turbulent dispersion via fan-generated flows

2014

View full text Add to dashboard Cite

Turbulent dispersion of passive scalar quantities has been extensively studied in wind tunnel settings, where the flow is carefully conditioned using flow straighteners and grids. Much less is known about turbulent dispersion in the "unconditioned" flows generated by fans that are ubiquitous in indoor environments, despite the importance of these flows to pathogen and contaminant transport. Here, we demonstrate that a point source of scalars released into an airflow generated by an axial fan yields a plume whose width is invariant with respect to the fan speed. The results point toward a useful simplification in modeling of disease and pollution spread via fan-generated flows.

show abstract

Measurements of pollen grain dispersal in still air and stationary, near homogeneous, isotropic turbulence

Cited by 45 publications

References 47 publications

Edge effects on the fluttering characteristics of freely falling planar particles

Edge effects on the fluttering characteristics of freely falling planar particles

Measurement of pollen clump release and breakup in the vicinity of ragweed (A. confertiflora) staminate flowers

Turbulent dispersion via fan-generated flows

Contact Info

Product

Resources

About