Plume structure

The plume structure data introduced in the previous sections provide the opportunity to assess whether multiple sensors that are spatially separated can rapidly acquire useful information [5], The correlation function for the instantaneous concentration acquired by two sensors at locations p and q, separated in the transverse direction, is defined as... 

Several laboratory studies have contributed to our understanding of turbulent chemical plumes and the effects of various flow configurations. Fackrell and Robins [25] released an isokinetic neutrally buoyant plume in a wind tunnel at elevated and bed-level locations. Bara et al. [26], Yee et al. [27], Crimaldi and Koseff [28], and Crimaldi et al. [29] studied plumes released in water channels from bed-level and elevated positions. Airborne plumes in atmospheric boundary layers also have been studied in the field by Murlis and Jones [30], Jones [31], Murlis [32], Hanna and Insley [33], Mylne [34, 35], and Yee et al. [36, 37], In addition, aqueous plumes in coastal environments have been studied by Stacey et al. [38] and Fong and Stacey [39], The combined information of these and other studies reveals that the plume structure is influenced by several factors including the bulk velocity, fluid environment, release conditions, bed conditions, flow meander, and surface waves. 

The release location influences the vertical distribution of the time-averaged concentration and fluctuations. For a bed-level release, vertical profiles of the time-averaged concentration are self-similar and agreed well with gradient diffusion theory [26], In contrast, the vertical profiles for an elevated release have a peak value above the bed and are not self-similar because the distance from the source to the bed introduces a finite length scale [3, 25, 37], Additionally, it is clear that the size and relative velocity of the chemical release affects both the mean and fluctuating concentration [4], The orientation of the release also appears to influence the plume structure. The shape of the profiles of the standard deviation of the concentration fluctuations is different in the study of Crimaldi et al. [29] compared with those of Fackrell and Robins [25] and Bara et al. [26], Crimaldi et al. [29] attributed the difference to the release orientation, which was vertically upward from a flush-mounted orifice at the bed in their study. 

The Reynolds number is the ratio of inertial to viscous forces and depends on the fluid properties, bulk velocity, and boundary layer thickness. Turbulence characteristics vary with Reynolds number in boundary layers [40], Thus, variation in the contributing factors for the Reynolds number ultimately influences the turbulent mixing and plume structure. Further, the fluid environment, air or water, affects both the Reynolds number and the molecular diffusivity of the chemical compounds. 

Based on the discussed example parameters that influence the turbulent mixing process, it is clear that plume structure can be described in general terms, but the specific characteristics are likely to be case dependent. Nevertheless, certain characteristics, such as those employed by the odor-gated rheotaxis with bilateral comparison strategy, may be similar enough to allow animals and engineered systems to track chemical plumes for a wide range of flow conditions. 

Reliable bioassays are indispensible for a successful isolation and identification of semiochemicals, especially pheromones. Recent improvements range from the construction of new olfactometers102 and the development of a delivery system for laboratory bioassays103 to measurements of odor plume structures in the wind tunnel104 and to a new method to improve olfactory responses to gas... 

Campbell I. H. and Griffiths R. W. (1990) Implications of mantle plume structure for the evolution of flood basalts. Earth Planet. Sci. Utt. 99, 79-93. 

Downwind of a canopy the cloud/plume structure resembles that in the wake of a wide obstacle of height H. Note that the concentration below the canopy is equal to the concentration at the top of the obstacles. 

A. Mafra-Neto and R.T. Carde, Influence of plume structure and pheromone concentration on upwind flight of caudra cautella males. Physiol. Entomol. 20 (1995) 117-133. 

Poudenx, R, and Kostiuk, L. W. "An Investigation of the Mean Plume Structures of a Flare in a Crosswind." Presented at The Combustion Institute, Canadian Section, 1999 Spring Technical Meeting, Edmonton, Alberta. 

The movement of a chemical substance within the vapor phase occurs by the combined driving forces of flow and diffusion. An illustration of these effects can be visualized by considering a smokestack plume in the absence of wind, the plume will rise vertically in a more or less uniform column until it reaches an elevation where density considerations result in its spreading out into a relatively broad and flat mantle. When wind is factored into the equation, the plume may move in a more nearly horizontal direction, more or less parallel to the surface of the ground, and at certain wind speeds the plume structure can break up into loops or bends due to turbulent aerodynamic effects such as eddy formation. In addition, small eddies can result in the breakdown of the coherent plume structure, with the formation of... 

A variety of experiments indicates clearly that animal orientation performance varies in different regimes as a result of changes in odor plume structure. This appears to reflect both the homogenization of the plume and the dilution of chemical concentration as the plume expands. 

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