The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Josef Daniel Ackerman - One of the best experts on this subject based on the ideXlab platform.
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Adding ecology to particle capture models: numerical simulations of capture on a moving cylinder in crossflow.
Journal of theoretical biology, 2014Co-Authors: Julian Krick, Josef Daniel AckermanAbstract:The particle capture efficiency, η, of systems that remove suspended particles from ambient flow (e.g. suspension feeding, abiotic pollination) has been studied using static collectors in steady flows. Particle deposition on collectors moving due to fluid flow remains largely unknown, despite its ecological relevance. We used numerical modeling to simulate particle deposition on a 2D circular cylinder subject to flow-induced oscillation in a cross flow. Using parameter values relevant to wind pollination and other natural biological systems, we examined the influence of the Direction, amplitude and frequency of the oscillation, the Stokes number (Stk=0.01-5, characterizing particle behavior), as well as the Reynolds number (Re=662 and 3309, characterizing flow regime) in steady and unsteady flow, on η. The numerical model was validated with empirical results for parts of the parameter space. Particle capture occurred via "inertial impaction", "Direct Interception" and "leeward deposition", as well as via a new mechanism, "collector chasing" for moving collectors. The η of an oscillating cylinder varied significantly relative to a static cylinder, depending on the parameters used, and on the magnitude of a numerical error that caused loss of particles. This variance of η was due to a change in relative momentum between the particle and the moving collector, which depends on Re, Stk and the oscillation parameters. Collector oscillation transverse to oncoming flow Direction strongly increased η, whereas collector motion parallel to flow had little effect on capture efficiency. The oscillation also changed leeward capture significantly in some cases. For most conditions, however, leeward deposition was small. Results suggest that collector motion could have significant influence on the particle capture efficiency of natural systems, which indicates the need to incorporate these ecologically more relevant findings into current models. Empirical studies, however, are still necessary to validate these results and provide reliable data.
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Submarine pollination in the marine angiosperm Zostera marina (Zosteraceae). I. The influence of floral morphology on fluid flow.
American journal of botany, 1997Co-Authors: Josef Daniel AckermanAbstract:An understanding of the process of submarine pollination should provide insight into the evolutionary and reproductive ecology of the marine angiosperms (seagrasses). The flow around the reproductive organs of the seagrass Zostera marina L. (Potamogetonales) was, therefore, examined in a flow chamber. The phenological emergence of flowers during (1) pollen capture and (2) pollen release, and by fruit during (3) seed release, led to a reduction in flow rate toward the inflorescence. This change in flow due to floral emergence was associated with a 50% increase in the fluid shear stress [tau = (2.2 _ 0.3) x 10-3 Pa for an immature flower vs. tau = (3.1 _ 0.5) x 10-3 Pa for a receptive flower]. The Reynolds number (Re) and fluid shear stress around inflorescences and infructescences were comparable, indicating a dynamic similarity in the processes of pollen capture and fruit dehiscence [Re = 47 _ 5, tau = (1.6 _ 0.3) x 10-3 Pa for inflorescences; Re = 38 _ 5, tau = (1.3 _ 0.1) x 10-3 Pa for infructescences]. These results indicate that the emergence of reproductive organs leads to changes in fluid shear stress, which will affect the release, transport, and capture of particles including pollen. Theoretical considerations of these observations using aerosol-filtration theory suggest that pollen capture in Z. marina occurs through Direct Interception of pollen by stigmas.
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Submarine pollination in the marine angiosperm Zostera marina (Zosteraceae). II. Pollen transport in flow fields and capture by stigmas.
American journal of botany, 1997Co-Authors: Josef Daniel AckermanAbstract:Flow chamber observations of the filamentous pollen of Zostera marina L. (Potamogetonales) revealed that pollen rotated and moved toward inflorescences where they were captured by stigmas. The mechanics of this abiotic pollination process were examined and found to be related to the flow environment around emergent flowers. The translational movement of pollen was imparted by the advection of the fluid (e.g., pollen kinetic energy, K, ranged from 0.8 x 10-14 to 2.4 x 10-14 J, and the average K of the fluid was _ 0.7 x 10-14 J), while the rotational motion was imparted by the fluid shear stress (tau) within the velocity gradient (e.g., pollen shear stress, sigmat = omegamu where omega is the rotational velocity and mu is the dynamic viscosity, ranged from 3.4 x 10-4 to 26 x 10-4 Pa, and the average fluid shear stress was tau _ 10 x 10-4 Pa; Ackerman, 1997, American Journal of Botany 84: 1099-1109). These results indicate that there is a greater potential for pollination by filamentous pollen relative to spherical pollen. Functionally, while spherical pollen needs to be Directly upstream from stigmas to be captured, filamentous pollen need only be in the vicinity of inflorescences and flowers to be captured by stigmas. Thus, in addition to Direct Interception on stigmas, filamentous pollen can be captured while they rotate past flowers or when they are reDirected through the velocity gradient towards flowers. Filamentous pollen is an adaptation to submarine pollination in seagrasses.
Emmanuel Waz - One of the best experts on this subject based on the ideXlab platform.
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Analysis of non-Brownian particle deposition from turbulent liquid-flow
AIChE Journal, 2016Co-Authors: Magali Dupuy, Herve Duval, Arunvady Xayasenh, Emmanuel WazAbstract:The deposition of non-Brownian particles from turbulent liquid-flow onto channel walls is numerically analyzed. The approach combines Lagrangian particle tracking with a kinematic model of the near-wall shear layer. For nonbuoyant particles, Direct Interception is the main deposition mechanism and the deposition velocity scales as the particle diameter (in wall units) to the power of 1.7. When wall/particle hydrodynamic interactions are taken into account, the deposition velocity is significantly reduced and the correction factor scales as the cubic root of the wall roughness to particle diameter ratio. For buoyant particles, sedimentation is usually the predominant deposition mechanism and the hydrodynamic interactions significantly affect the deposition velocity when the drainage characteristic time driven by buoyancy is of the order of the particle residence time close to the wall. Last, a wall-function for the suspended particles is proposed.
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Analysis of non‐Brownian particle deposition from turbulent liquid‐flow
AIChE Journal, 2015Co-Authors: Magali Dupuy, Herve Duval, Arunvady Xayasenh, Emmanuel WazAbstract:The deposition of non-Brownian particles from turbulent liquid-flow onto channel walls is numerically analyzed. The approach combines Lagrangian particle tracking with a kinematic model of the near-wall shear layer. For nonbuoyant particles, Direct Interception is the main deposition mechanism and the deposition velocity scales as the particle diameter (in wall units) to the power of 1.7. When wall/particle hydrodynamic interactions are taken into account, the deposition velocity is significantly reduced and the correction factor scales as the cubic root of the wall roughness to particle diameter ratio. For buoyant particles, sedimentation is usually the predominant deposition mechanism and the hydrodynamic interactions significantly affect the deposition velocity when the drainage characteristic time driven by buoyancy is of the order of the particle residence time close to the wall. Last, a wall-function for the suspended particles is proposed. © 2015 American Institute of Chemical Engineers AIChE J, 2015
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ANALYSIS OF PARTICLE DEPOSITION FROM TURBULENT LIQUID-FLOW ONTO SMOOTH CHANNEL WALLS
2014Co-Authors: Magali Dupuy, Pierre Brun, Arunvady Xayasenh, Emmanuel Waz, Herve DuvalAbstract:In this study, we analyse the motion of hydrosol particles in the near-wall shear layer of a turbulent channel flow. The liquid flow-field is described using the kinematic model proposed by Fan and Ahmadi (1995) combined with Lagrangian particle tracking. Numerical simulations were performed for friction velocity ranging from 1.5 mm. to 15 mm. , particle diameter from 5 to 50, particle to liquid density ratio from 1 to 1.4 and wall roughness height from to. The results show that the inertia effects are very weak. For nonbuoyant particles, Direct Interception is the main deposition mechanism and a law giving the deposition velocity as a function of the different parameters is proposed. For buoyant particles the deposition is controlled by sedimentation for the smallest values of friction velocity. When friction velocity increases, the Direct Interception contribution increases as well, and may prevail on sedimentation.
Guoquan Zhang - One of the best experts on this subject based on the ideXlab platform.
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Deposition of Particles on a Single Cylinder by a Coulombic Force and Direct Interception
Aerosol Science and Technology, 1993Co-Authors: Ian Colbeck, Guoquan ZhangAbstract:The deposition efficiency of particles on a single cylinder by a coulombic force and Direct Interception is theoretically investigated by combining the methods of Duchin-Deryaguin and Pich. The cases in which the particles and cylinder are charged with same and reverse sign are considered, also with potential and viscous flows. The results obtained are compared with existing theories and experiments.
T. Blanuša - One of the best experts on this subject based on the ideXlab platform.
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The influence of plant type on green roof rainfall retention
Urban Ecosystems, 2019Co-Authors: S. Kemp, P. Hadley, T. BlanušaAbstract:Green roofs can mitigate the flood risk by reducing the volume of runoff through Direct Interception and subsequent evapotranspiration (ET), but the planting choices can influence the extent of this service. Glasshouse experiments were carried out in spring/summer using simulated rainfall to compare the rainfall retention capacity of three physiologically active broadleaf species ( Heuchera micrantha , Salvia officinalis and Stachys byzantina ), which have previously shown to provide improved rooftop cooling, to an industry standard green roof species, Sedum spurium . Furthermore, the impact of varying ambient temperature and humidity conditions on the ability of these species to restore the substrate retention capacity through ET was also tested in a series of controlled-environment experiments simulating a range of potential UK summertime scenarios. Canopies alone retained up to 17% ( Sedum ) of the total rainfall in this study, with Salvia and Stachys also retaining in excess of 10%, and can make a substantial contribution to rainfall retention on a green roof. Rainfall retention was also strongly correlated with total ET in the preceding 72 h (R^2 = 0.94; P
Magali Dupuy - One of the best experts on this subject based on the ideXlab platform.
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Analysis of non-Brownian particle deposition from turbulent liquid-flow
AIChE Journal, 2016Co-Authors: Magali Dupuy, Herve Duval, Arunvady Xayasenh, Emmanuel WazAbstract:The deposition of non-Brownian particles from turbulent liquid-flow onto channel walls is numerically analyzed. The approach combines Lagrangian particle tracking with a kinematic model of the near-wall shear layer. For nonbuoyant particles, Direct Interception is the main deposition mechanism and the deposition velocity scales as the particle diameter (in wall units) to the power of 1.7. When wall/particle hydrodynamic interactions are taken into account, the deposition velocity is significantly reduced and the correction factor scales as the cubic root of the wall roughness to particle diameter ratio. For buoyant particles, sedimentation is usually the predominant deposition mechanism and the hydrodynamic interactions significantly affect the deposition velocity when the drainage characteristic time driven by buoyancy is of the order of the particle residence time close to the wall. Last, a wall-function for the suspended particles is proposed.
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Analysis of non‐Brownian particle deposition from turbulent liquid‐flow
AIChE Journal, 2015Co-Authors: Magali Dupuy, Herve Duval, Arunvady Xayasenh, Emmanuel WazAbstract:The deposition of non-Brownian particles from turbulent liquid-flow onto channel walls is numerically analyzed. The approach combines Lagrangian particle tracking with a kinematic model of the near-wall shear layer. For nonbuoyant particles, Direct Interception is the main deposition mechanism and the deposition velocity scales as the particle diameter (in wall units) to the power of 1.7. When wall/particle hydrodynamic interactions are taken into account, the deposition velocity is significantly reduced and the correction factor scales as the cubic root of the wall roughness to particle diameter ratio. For buoyant particles, sedimentation is usually the predominant deposition mechanism and the hydrodynamic interactions significantly affect the deposition velocity when the drainage characteristic time driven by buoyancy is of the order of the particle residence time close to the wall. Last, a wall-function for the suspended particles is proposed. © 2015 American Institute of Chemical Engineers AIChE J, 2015
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ANALYSIS OF PARTICLE DEPOSITION FROM TURBULENT LIQUID-FLOW ONTO SMOOTH CHANNEL WALLS
2014Co-Authors: Magali Dupuy, Pierre Brun, Arunvady Xayasenh, Emmanuel Waz, Herve DuvalAbstract:In this study, we analyse the motion of hydrosol particles in the near-wall shear layer of a turbulent channel flow. The liquid flow-field is described using the kinematic model proposed by Fan and Ahmadi (1995) combined with Lagrangian particle tracking. Numerical simulations were performed for friction velocity ranging from 1.5 mm. to 15 mm. , particle diameter from 5 to 50, particle to liquid density ratio from 1 to 1.4 and wall roughness height from to. The results show that the inertia effects are very weak. For nonbuoyant particles, Direct Interception is the main deposition mechanism and a law giving the deposition velocity as a function of the different parameters is proposed. For buoyant particles the deposition is controlled by sedimentation for the smallest values of friction velocity. When friction velocity increases, the Direct Interception contribution increases as well, and may prevail on sedimentation.
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Direct numerical simulation of oxide inclusion turbulent deposition at liquid steel/slag interface
2013Co-Authors: Arunvady Xayasenh, Magali Dupuy, Laurent Joly, Herve DuvalAbstract:The present study focuses on the inclusion behaviour near the liquid metal/slag interface. Inclusion turbulent deposition is investigated using Direct numerical simulation of the liquid flow combined with Lagrangian particle tracking under conditions of one-way coupling. The interface is modelled as a non-deformable free-slip surface. Unsheared turbulence is generated by random forcing in a finite-height region parallel to the free-slip surface. In between, the turbulence diffuses toward the free surface. The inclusions are randomly introduced in the forcing region and tracked through the diffusion region up to the interface. In the particle dynamic equation, the buoyancy force, the Stokes drag, the pressure drag and the added mass are considered. Close to the interface, the hydrodynamic interactions (i.e. lubrication effects) between the inclusion and the free surface may be taken into account as well as the Van der Waals forces. Numerical simulations were performed with surface Reynolds numbers ranging from 68 to 235. The inclusion diameter varied between 10-5 m and 5.10-5 m and the particle to liquid density ratio between 0.5 and 1. For these sets of parameters, it appears that the inertia effects are very weak. The deposition of buoyant inclusions is controlled by sedimentation whereas for nonbuoyant inclusions, Direct Interception is the only deposition mechanism. In the latter case, the deposition velocity strongly depends on. It is shown that the deposition velocity made dimensionless by the free surface characteristic velocity scales as the inclusion diameter made dimensionless by the Kolmogorov length scale calculated at the free surface. Lastly, the effect of lubrication is examined: it can significantly reduce the Direct Interception contribution of the deposition velocity.