Aerodynamics

Kundu, Pijush K.

doi:10.1016/b978-0-12-405935-1.00014-9

Cited by 119 publications

(191 citation statements)

References 2 publications

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“…In addition to this mechanical constraint, an upward pressure force due to lubrication between the particles and the wall may become significant when the distance is less than one major axis length, which would suppress both the concentration and settling velocity in this region (Kundu et al. 2012). The lubrication effect would be stronger for disks than fibres due to their larger planar area, which may explain why the near-wall concentration deficit is larger for disks than for fibres.…”

Section: Resultsmentioning

confidence: 99%

“…One mechanism for particle tumbling near the wall is the direct interaction with the wall itself. Due to the particles’ extended dimensions and finite slip velocity, friction due to direct contact or lubrication (Kundu, Cohen & Dowling 2012) with the wall could exert significant torques on particles. To isolate the effect of wall contact, we consider particles located within one semimajor axis length from the wall and compare between those that are contacting the wall and those that are not.…”

Section: Resultsmentioning

confidence: 99%

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Experimental investigation of inertial fibres and disks in a turbulent boundary layer

Baker

Coletti²

2022

J. Fluid Mech.

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We study experimentally the behaviour of negatively buoyant disks and fibres in a turbulent boundary layer. The regime is relevant to the transport of natural sediment or plastic particles in water, with density ratio $\rho _p/\rho _f \sim O(1)$ , major axis lengths $D_p^+ \sim 50$ , friction Stokes numbers $\mbox { {St}}^+ \sim O(10)$ and friction Reynolds number $\mbox { {Re}}_\tau = 620$ . The translational and rotational motion, as well as concentration and dispersion, are compared with those of spheres of similar inertia. Disks and fibres both oversample high-speed fluid near the wall, in agreement with particle-resolved numerical simulations. Fibres tend to orient mostly in the streamwise direction while disks maintain their symmetry axis quasi-normal to the wall. This alignment is more stable for disks than for fibres: the latter undergo strong tumbling near the wall in response to the mean shear and turbulent fluid velocity fluctuations, whereas the former wobble about their preferential wall-normal orientation. The translational and rotational accelerations indicate that, despite the nominal relaxation times being similar, the disks are slower than the fibres in responding to wall turbulence. For both, wall contact causes strong and intermittent tumbling. The concentration profiles follow Rouse–Prandtl theory over a limited portion of the boundary layer, deviating near the wall and in the outer region. This is largely due to the non-uniform settling velocity, which decreases steeply approaching the wall for all particle types. This is, in turn, a consequence of the reduced particle diffusivity, which closely matches the profile of the eddy viscosity.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Experimental investigation of inertial fibres and disks in a turbulent boundary layer

Baker

Coletti²

2022

J. Fluid Mech.

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“…However, since the heat source (namely, the cotton patch) is positioned on the wall of the cuvette, where the liquid flow vanishes (due to the no-slip boundary condition), the heat gradients in the vicinity of the heat source are not reduced as efficiently by the stirring as in the bulk of the sample. Indeed, Figure (a) shows that the azimuthal flow velocity (parallel to the cuvette wall) forms the well-known boundary layer , whereby the flow velocity drops linearly toward the cuvette wall. As a result, heat drainage away from the heat source position is not as effective as in other parts of the sample.…”

Section: Representative Analysismentioning

confidence: 97%

The Role of Heat Generation and Fluid Flow in Plasmon-Enhanced Reduction–Oxidation Reactions

Sivan

2021

ACS Photonics

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Recently, we have shown that thermal effects play a crucial role in speeding up the rate of bond-dissociation reactions. This was done by applying a simple temperature-shifted Arrhenius law to the experimental data, corroborated with a detailed account of the heat diffusion occurring within the relevant samples and identification of errors in the temperature measurements. Here, we provide three important extensions of our previous studies. First, we analyze thermal effects in reduction−oxidation (redox) reactions, where charge transfer is an integral part of the reaction. Second, we analyze not only the spatial distribution of the temperature but also its temporal dynamics. Third, we also model the fluid convection and stirring. An analysis of two exemplary experimental studies allows us to show that thermal effects can explain the experimental data in one of the experiments (Baumberg and co-workers) but not in the other (Jain and co-workers), showing that redox reactions are not necessarily driven by nonthermal charge carriers.

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“…Previous theoretical approaches to this problem have either been in terms of variables that are difficult to control experimentally, such as the array growth rate, or have only analyzed the dominant interactions, without providing practical guidelines for the fabrication of these structures . To capture the effect of the relevant parameters in the opal coverage, we studied the fluid dynamics of the self-assembly process with the lubrication approximation , (a detailed derivation is provided in Section S5 of the Supporting Information). This approach allows us to obtain a governing equation for the effect of gravity and evaporation on the evolution of the liquid thickness over the substrate h ( x , t ) where μ, ρ, and ṁ evap ″ are the viscosity, density, and evaporation flux (kg/m 2 s) of the solution, respectively.…”

Section: Resultsmentioning

confidence: 99%

Rational Fabrication of Nano-to-Microsphere Polycrystalline Opals Using Slope Self-Assembly

et al. 2021

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Self-assembly of artificial opals has garnered significant interest as a facile nanofabrication technique capable of producing highly ordered structures for optical, electrochemical, biomolecular, and thermal applications. In these applications, the optimum opal particle diameter can vary by several orders of magnitude because the properties of the resultant structures depend strongly on the feature size. However, current opal fabrication techniques only produce high-quality structures over a limited range of sphere sizes or require complex processes and equipment. In this work, the rational and simple fabrication of polycrystalline opals with diameters between 500 nm and 10 μm was demonstrated using slope self-assembly of colloids suspended in ethanol–water. The role of the various process parameters was elucidated through a scaling-based model that accurately captures the variations of opal substrate coverage for spheres of size 2 μm or smaller. For spheres of 10 μm and larger, capillary forces were shown to play a key role in the process dynamics. Based on these insights, millimeter-scale monolayered opals were successfully fabricated, while centimeter-scale opals were possible with sparse sphere stacking or small uncovered areas. These insights provide a guide for the simple and fast fabrication of opals that can be used as optical coatings, templates for high power density electrodes, molecule templates, and high-performance thermo-fluidic devices.

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Aerodynamics

Cited by 119 publications

References 2 publications

Experimental investigation of inertial fibres and disks in a turbulent boundary layer

Experimental investigation of inertial fibres and disks in a turbulent boundary layer

The Role of Heat Generation and Fluid Flow in Plasmon-Enhanced Reduction–Oxidation Reactions

Rational Fabrication of Nano-to-Microsphere Polycrystalline Opals Using Slope Self-Assembly

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