The slip velocity of nearly neutrally buoyant tracers for large-scale PIV

Faleiros, David Engler; Tuinstra, Marthijn; Sciacchitano, Andrea; Scarano, Fulvio

doi:10.1007/s00348-021-03274-9

Cited by 6 publications

(6 citation statements)

References 46 publications

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“…We begin by summarizing previous results on inertial particle dynamics [19,20] using the Maxey-Riley equation [21], which predicts the motion of a small spherical particle of density ρ p , diameter d p , and velocity V p in a fluid of dynamic viscosity µ, density ρ f and velocity U. After introducing corrections for finite particle Reynolds number, the force balance reads [19]…”

Section: Inertial Particle Dynamicsmentioning

confidence: 99%

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Lagrangian particle tracking in the atmospheric surface layer

Conlin,

Even,

Wei

et al. 2024

Meas. Sci. Technol.

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Field measurements in the atmospheric surface layer (ASL) are key to understanding turbulent exchanges in the atmosphere, such as fluxes of mass, water vapor, and momentum. However, current field measurement techniques are limited to single-point time series or large-scale flow field scans. Extending image-based laboratory measurement techniques to field-relevant scales is a promising route to more detailed atmospheric flow measurements, but this requires significant increases in the attainable measurement volume while keeping the spatiotemporal resolution high. Here, we present an adaptable particle tracking system using helium-filled soap bubbles, mirrorless cameras, and high-power LEDs enabling volumetric ASL field measurements. We conduct analyses pertinent to image-based field measurement systems and develop general guidelines for their design. We validate the particle tracking system in a field experiment. Single-point Eulerian velocity statistics are presented and compared to data from concurrently operated sonic anemometers. Lagrangian displacement statistics are also presented with a comparison to Taylor’s theory of dispersion. The system improves the state-of-the-art in field measurements in the lower atmosphere and enables unprecedented insights into flow in the ASL.

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Section: Inertial Particle Dynamicsmentioning

confidence: 99%

“…Transfer function analysis shows how the influence of different forces varies with St [19,20,23,24]. Inserting V p = Vp e −iωt and U = Ûe −iωt into equation (1) the ratio H = Vp / Û can be derived, which describes the attenuation, or amplification, of fluid velocity fluctuations by the particle…”

Section: Inertial Particle Dynamicsmentioning

confidence: 99%

Lagrangian particle tracking in the atmospheric surface layer

Conlin,

Even,

Wei

et al. 2024

Meas. Sci. Technol.

View full text Add to dashboard Cite

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“…The last (fifth) term describes the temporal development of the boundary layer surrounding the particle (e.g., thickening) and therefore results in a memory term. This so-called Basset history term is often ignored in the studies considering heavy particles, however, there is an increasing number of recent studies demonstrating that it has a significant influence when the particle is close to neutrally buoyant [22][23][24][25][26][27]. Incorporating this history term is very costly not only in terms of computation but also the memory requirement due to the very slowly decaying kernel, therefore we opted for the efficient second-order method of van Hinsberg et al [26].…”

Section: Particle Solvermentioning

confidence: 99%

Direct numerical simulation of the distribution of floating microplastic particles in an open channel flow

Sakai

Manhart

2023

Applied Research

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Microplastic fragments in the aquatic environment constitute a major threat for the health and fitness of organisms. However, our quantitative understanding in the microplastic load in typical natural river systems is severely limited due to the large uncertainties associated with the sources and the pathways of the microplastic contamination. To address this knowledge gap, we performed direct numerical simulations of the dynamics and distribution of microplastic particles in turbulent open channel flow at moderate Reynolds numbers. The particle dynamics is characterised by four nondimensional parameters, namely: Reynolds number of the open channel flow (), nondimensional particle diameter () and Galileo () and Stokes () numbers of the particles of which the latter two include the particle‐fluid density ratio (). To limit our scope to the most relevant configuration, we focused on the distribution of weakly buoyant microplastic particles at , whereas the remaining parameters were adjusted to cover the orders of magnitude that can be found in a typical laboratory facility, as well as a natural river. Our simulation results show that the steady‐state microplastic distribution in the turbulent flow is influenced by the Stokes and the Galileo numbers significantly, which ranges from the complete accumulation on the free surface to the homogeneous distribution, and somewhere in between. Moreover, the Galileo number, alongside the flow Reynolds number, were also shown to influence the temporal scaling of the transient behaviour of the gradual accumulation of the microplastics towards the free surface. Both of our findings highlight the complex nature of the particle–turbulence interactions, and motivate further investigations in this approach.

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“…The glare point diameter in the object space depends not only on the bubble size but also on the imaging conditions, since these affect the subtended angle of light captured by the lens. As discussed by Faleiros et al (2021), this may be approximated as:…”

Section: Imagingmentioning

confidence: 99%

On the scalability of PIV experiments with helium filled soap bubbles

Guerra,

Scarano,

Sciacchitano

2023

Preprint

Self Cite

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The scalability of experiments using PIV relies upon several parameters, namely illumination power, camera sensor and primarily the tracers light scattering capability. Given their larger cross section, helium-filled soap bubbles (HFSB) allow measurements in air flows over a significantly large domain compared to traditional oil or fog droplets. Controlling their diameter translates into scalability of the experiment. This work presents a technique to extend the control of HFSB diameter by geometrical variations of the generator. The latter expands the more limited range allowed by varying the relative helium-air mass flow rates. A theoretical model predicts the bubble size and production rate, which is verified experimentally by high-speed shadow visualization. The overall range of HFSB produced in a stable (bubbling) regime varies from 0.16 mm to 2.7 mm. Imaging by light scattering of such tracers is also investigated, in view of controversies in the literature on whether diffraction or geometrical imaging dominate the imaging regime. The light scattered by scaled HFSB tracers is imaged with a high-speed camera orthogonal to the (LED) illumination. Both the total energy collected on the sensor for a single tracer, as well as its peak intensity are found to preserve scaling with the square of the diameter at object magnification of 10-1 or below, typical of PIV experiments. For large-scale volumetric applications, it is shown that varying the bubble diameter allows increasing both the measurement domain as well as the working distance of the imagers at 10 m and beyond. A scaling rule is proposed for the latter.

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The slip velocity of nearly neutrally buoyant tracers for large-scale PIV

Cited by 6 publications

References 46 publications

Lagrangian particle tracking in the atmospheric surface layer

Lagrangian particle tracking in the atmospheric surface layer

Direct numerical simulation of the distribution of floating microplastic particles in an open channel flow

On the scalability of PIV experiments with helium filled soap bubbles

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