Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session J37: Turbulence: Particle laden flows |
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Chair: Facundo Cabrera, Portland State University; Jesse Capecelatro, University of Michigan Room: 245 |
Sunday, November 20, 2022 4:35PM - 4:48PM |
J37.00001: DNS of droplet-laden homogeneous shear turbulence Pablo I Trefftz Posada, Antonino Ferrante We have studied the effects of droplets on the evolution of incompressible homogeneous shear turbulence (HST) via direct numerical simulation (DNS). We performed DNS of droplet-laden HST using a mesh of 1200 × 600 × 600 grid points for a Reynolds number based on the Taylor length-scale of turbulence (λ) at the droplets' release-time of Reλ = 53. The flow was randomly seeded with 1260 droplets (equivalent to 5% droplet volume-fraction) of diameter approximately equal to twice λ. For the cases studied, we varied the initial Weber number based on the r.m.s. velocity of the carrier flow, Werms, from 0.02 to 0.5 while keeping the density and viscosity ratios constant (ρd/ρc = 10 and μd/μc = 10). The results show that for Werms = 0.02 and Werms = 0.5, the production of turbulence kinetic energy (TKE) is larger and smaller than that of the droplet-free case, respectively, and that increasing Werms causes a decrease in TKE production. We explain the modulation due to the droplets of TKE production and power of the surface tension, respectively, through the droplet "catching-up" and the droplet "shearing" mechanisms. |
Sunday, November 20, 2022 4:48PM - 5:01PM |
J37.00002: Exploring the parametric dependence of particle settling and preferential sweeping in two-way coupled turbulent flows Soumak Bhattacharjee, Josin Tom, Maurizio Carbone, Andrew D Bragg In Tom & Bragg (2019), we investigated the role of different scales of turbulence affecting the settling of inertial particles, advancing the idea of the preferential sweeping mechanism (Maxey 1987), which only applied to weakly inertial particles. Building upon this theory, in Tom, Carbone & Bragg (2022), we studied how the multiscale preferential sweeping mechanism enhances the settling velocities of two-way coupled particles in the dilute particle mass loading regime. We confirmed Monchaux's (2017) observation that even in this regime, two-way coupling can significantly enhance particle settling, even though the global fluid statistics are almost unaffected. However, in contrast to Monchaux (2017), we found that preferential sweeping still plays a crucial role in the settling enhancement in the limited parameter regime considered. Here we perform direct numerical simulation (DNS) to study the problem over a much larger portion of the parameter regime. We aim to understand how the conclusions of Tom, Carbone & Bragg (2022) change if the Froude number and mass loading are varied over a much wider range than were considered in that study. |
Sunday, November 20, 2022 5:01PM - 5:14PM |
J37.00003: Experiments on inertial particles in turbulent flows under microgravity. Facundo Cabrera, Karl J Cardin, Nicolas Plihon, Mickaël Bourgoin, Raúl Bayoán B Cal The dynamics of inertial particles in turbulent flows is composed of several physical ingredients that are entangled by gravity; namely particle settling and particle-turbulence couplings. Thus the study of particle-laden turbulent flows in a microgravity environment disentangles these effects and allows to successfully measure particle-turbulence couplings effects, independently of gravity effects. |
Sunday, November 20, 2022 5:14PM - 5:27PM |
J37.00004: Near-wall particle dynamics in a turbulent channel flow Miguel X Diaz-Lopez, Matt Gorman, Rui Ni The interaction of particles with turbulence close to the wall is relevant to many applications such as particle deposition in jet engines, dust transport and sedimentation in atmospheric boundary layers. The way these particles interact with the wall through collision is of particular interest because many forces play important roles, including the turbophoretic force and electrostatic imaging force. It is often difficult to separate their contribution in complicated wall-bounded turbulence. This study focuses on a new diagnostic technique which relies on using the image of a particle off a reflective surface as a way to determine the collision moment and location as well as the electrostatic imaging force. Ongoing efforts with this system will elucidate near-wall particle dynamics and collisions to better understand the dynamics of particle-wall and particle-turbulence interactions. |
Sunday, November 20, 2022 5:27PM - 5:40PM |
J37.00005: The dynamics of charged particles in a turbulent channel flow Matt Gorman, Miguel X Diaz-Lopez, Rui Ni Experiments in a new vertical channel were conducted to probe the dynamics of charged particles in turbulence. Particles, charged after passing through an ionization section at the top of the channel, are subjected to interactions with both the turbulent flow and an external electric field. To obtain particle statistics in the near-wall region, three high-speed cameras are used to capture particle trajectories in both the wall-normal and wall-parallel planes. The electric Stokes number, which is sensitive to changes in the particle charge and the external electric field, is varied throughout these experiments to explore conditions in which electrostatic effects play a significant role in the particle dynamics. These experiments reveal how electrostatic effects alter particle clustering in turbulent boundary layers and provide insight into the relationship between electrostatics and turbulence in the modulation of particle-laden flows. |
Sunday, November 20, 2022 5:40PM - 5:53PM |
J37.00006: Markov property of Lagrangian turbulence Joachim Peinke, André Fuchs, Martin Obligado, Mickael Bourgoin, Mathieu Gibert, Pablo Mininni Based on direct numerical simulations with point-like inertial particles, with Stokes numbers St = 0,0.5, 3, and 6, transported by homogeneous and isotropic turbulent flows, we present in this letter for the first time evidence for the existence of Markov property in La- grangian turbulence. We show that the Markov property is valid for a finite step size larger than a Stokes-number–dependent Einstein-Markov coherence time scale. This enables the de- scription of multi-scale statistics of Lagrangian particles by Fokker-Planck equations, which can be embedded in an interdisciplinary approach linking the statistical description of turbulence with fluctuation theorems of non-equilibrium stochastic thermodynamics and local flow structures. The formalism allows estimation of the stochastic thermodynamics entropy exchange associated with the particles Lagrangian trajectories. Entropy-consuming trajectories of the particles are related to specific evolution of velocity increments through scales and may be seen as intermittent struc- tures. Statistical features of Lagrangian paths and entropy values are thus fixed by the fluctuation theorems. |
Sunday, November 20, 2022 5:53PM - 6:06PM |
J37.00007: Large eddy simulation of turbulent particle-laden flows: effects of sub-grid scale fluctuations on dispersion and deposition of particles Farid Rousta, Goodarz Ahmadi, Bamdad Lessani Large-eddy and direct numerical simulations (LES/DNS) coupled with Lagrangian particle tracking were performed to study the effects of sub-grid scale (SGS) fluctuations on the dispersion and deposition of particles. A total of eight cases with particle Stokes numbers ranging from St=2 to St=100 with friction Reynolds numbers of Reτ = 180 and Reτ = 360 were considered. First, the fluid velocity seen by particles was assumed to be the LES filtered velocity. Then, particle deposition and dispersion with this assumption were compared with direct numerical simulation (DNS) results at the same condition to clarify the effect of SGS fluctuations. Considerable differences in deposition and dispersion of particles were observed, especially for the particles with lower Stokes number and higher friction Reynolds number. |
Sunday, November 20, 2022 6:06PM - 6:19PM |
J37.00008: On divergence, curl, and helicity of the inertial particle velocity in a 4-way coupled channel flow Kai Schneider, Thibault OUJIA, Jacob R West, Keigo Matsuda, Suhas S Jain, Kazuki Maeda Inertial particle data from three-dimensional direct numerical simulations of dilute, four-way coupled particle-laden turbulent channel flow at Reτ ≈ 230 are analyzed. Delaunay tessellation is applied to the particle positions considering a range of mass loading (10\%-300\%) and particle inertia (St+ ≈ 1-60). Using finite-time measures, we then quantify the divergence and rotation of the particle velocity and determine likewise the particle flow helicity (Oujia et al. J. Fluid Mech., 2020; Oujia et al. TSFP-12, 2022). Statistical analyses of divergence, curl, and helicity are performed, along with their dependence on the wall distance, to assess the influence of the flow anisotropy. The probability distribution functions (PDFs) of the divergence and curl show that the particle inertia affects the tails of the PDFs, which implies extreme events. Joint PDFs of the divergence and the Delaunay volume further clarifies if the divergence is most prominent in the cluster regions or in the void regions. The PDFs of the inertial particle vorticity are compared to those of the fluid vorticity and they are found to deviate from a Laplace distribution. Finally, PDFs of the particle flow helicity show that swirling motion has the tendency to be suppressed for sufficiently large particle inertia. The relationship with sweep and ejection motion of the particles will be discussed. |
Sunday, November 20, 2022 6:19PM - 6:32PM |
J37.00009: Effects of particle-laden environments on large-scale solar photovoltaic plants Sarah E Smith, Marc Calaf, Raúl B Cal, Henda Djeridi, Martin Obligado Wind-propelled debris in solar photovoltaic (PV) plants diminishes efficiency and damages panel structures. Dust particles ranging from 1 to 300 μm accumulate and heat panel surfaces, reducing generation up to 35% even in mild conditions. Greater velocities and mixing launch larger objects, increasing deposition rates and fatigue-load impact. Previous works address individual panel loading, but little is known about particle trajectories in panel wakes of PV arrays. In this study, we explore the behavior of particle-laden flow within turbulent, multi-row solar farm canopies and discuss the role of PV design variations on turbulent particle interactions. Wind tunnel experiments vary module orientation and imposed environmental conditions as observed in open landscapes. Flow behavior is captured via particle image velocimetry (PIV) in the wakes of subsequent model PV panels. Variations such as inflow velocity (U_∞= 2.5 to 10 m/s), array configuration (e.g. angle, spacing), particle concentration (ϕ_v= 0 to 2 × 10^5), and turbulence intensity represent a range of operating solar farm conditions. Results inform on fundamental behavior of particles in turbulent flat plate array wakes, while giving insight toward mitigating adverse effects of debris-laden impact on PV farm generation. |
Sunday, November 20, 2022 6:32PM - 6:45PM |
J37.00010: Encounter rates of elongated phytoplankton in turbulence José-Agustín Arguedas-Leiva, Jonasz J Slomka, Cristian C Lalescu, Roman Stocker, Michael Wilczek Phytoplankton come in a variety of shapes, however, elongated morphologies dominate. While aspect ratios above 5 are quite common for individual cells, chain-forming species can exhibit aspect ratios greater than 100. How cell shape affects encounter rates between phytoplankton in mild turbulence has been an open question. In this contribution, we present results from direct numerical simulations of elongated phytoplankton cells in turbulence, showing that encounters between elongated cells are significantly enhanced compared to spherical cells. Consequently, the timescales of marine snow formation are smaller for elongated cells than for spherical cells, which offers a potential explanation for the rapid clearance times of many phytoplankton blooms. |
Sunday, November 20, 2022 6:45PM - 6:58PM Author not Attending |
J37.00011: Algal Population in Light-Limited Conditions Filippo De Lillo, Guido Boffetta, Matteo Borgnino We investigate the population dynamics of phytoplankton (photosynthetic, one-celled algae) in turbulent waters, in conditions where light can be considered as the limiting factor for growth1. In such conditions, the negative buoyancy characterizing most phytoplankters, would condemn the population to sinking out of the photic zone at the top of the ocean, towards the dark deep waters. Turbulence may resuspend them long enough to reproduce and reach a stationary population. While classic models for the development of algal blooms are one-dimensional and purely diffusive, recent numerical investigations point to the relevance of the different flow scales for bloom conditions3,4. We perform numerical simulations of a turbulent flow to study how the population correlates with the flow and how the large-scale and small-scale components of turbulence influence the vertical profile and horizontal inhomogeneity of the population and its fluctuations. 1 De Lillo et al. (in preparation, 2022). 2 Huisman et al., Limnol. Oceanogr. 44, 1781 (1999). 3 Tergolina et al., Phys. Rev. E 104, 065106 (2021). |
Sunday, November 20, 2022 6:58PM - 7:11PM |
J37.00012: Dynamics of complex snowflakes in a broad range of surface-atmosphere turbulence Dhiraj K Singh, Eric R Pardyjak, Timothy J Garrett We present the first direct measurements of Lagrangian snowflake trajectories and their microphysical properties, mass, and density in surface-layer atmospheric turbulence. We deployed three primary instruments at the Alta-Collins snow study plot at a high elevation site in Utah: a 3-D sonic anemometer, a snowflake velocity laser-tracking system, and the Differential Emissivity Imaging Disdrometer (DEID), which provides precise estimates of hydrometeor mass, density, and size. The particle tracking system measured the actual fall velocity of snowflakes in a turbulent atmosphere. In contrast, the snowflake terminal velocity in still air was derived from DEID microphysical measurements using well-known aerodynamic formulations. We observed a broad range of turbulence and particle conditions covering Kolmogorov-scale Stokes numbers ($St$) and Reynolds numbers $R_{\lambda}$ ranging from 0.12 to 3.50 and from 400 to 70,000, respectively. The actual fall velocity is found to be greater and less than the associated terminal velocity in still air, indicating that turbulence enhances (sweeping) and reduces (loitering) settling, depending on conditions. We find for a very broad range of turbulence where the probability distribution function of normalized individual Lagrangian snowflake accelerations follows a Laplacian distribution ($exp(-3/2 a/a_{rms}$)) with a nearly constant slope -3/2, which is independent of $St$ and $R_{\lambda}$.Surprisingly, an identical Laplacian distribution applied to pseudo-accelerations was calculated from Eulerian temporal variability in both observed snowflakes mean vertical velocities and the mean terminal fall velocity expected in still air. Furthermore, fat tails compose 1\% of acceleration distribution with values as high as 142\,m\,s$^{-2}$ However, the question remains to be determined why the value of the coefficient is $3/(2 a_{\rm{rms}})$ in the distribution of Lagrangian and Eulerian |
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