Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session A22: Particle-Laden Flows: General I |
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Chair: Martin Obligado, Laboratoire de Mecanique des Fluides de Lille Room: 250 F |
Sunday, November 24, 2024 8:00AM - 8:13AM |
A22.00001: Aerodynamics of the square-back Ahmed body under rainfall and turbulent conditions Martin Obligado, Nicolas Mazellier We report an experimental investigation on the aerodynamics of the square-back Ahmed body, a simplified road vehicle, under rainfall conditions and different background turbulent flows. Wind tunnel tests using different grids (passive and active) and a uniform grid of injectors installed upstream of the body were used to characterize both the bi-stability and the base drag of the body. With this aim, a set of 81 pressure taps was installed at the body base. To study the role of rainfall in the dynamics of the Ahmed body, three different volume fractions of droplets were injected under passive-grid-generated turbulence conditions. On the other hand, the role of the turbulent inflow was assessed by testing the body in dry conditions, in an empty test section (laminar inflow), and under passive-grid- (low turbulence intensity) and active-grid-generated (moderate-to-high intensity) turbulence. |
Sunday, November 24, 2024 8:13AM - 8:26AM |
A22.00002: Direct Numerical Simulations of the particle laden flow over a cylinder Siddhi Arya, Partha S Goswami Fluid flow around the bluff body has applications in various industrial fields and natural phenomena. Particles present in the flow add to the complexity due to interaction between the particle and fluid phases as well as particle collisions that can lead to flow modification. Our initial DNS study on particle clustering in a vertical channel flow showed that particle dispersion in the flow is greatly affected by the Reynolds number, particle Stokes number and mass loading. The cluster area is found to be larger at the channel center in comparison to the near-wall region. Also, turbulence suppression is observed at higher particle loading leading to uniform particle distribution. The current study focuses on the effect of Reynolds number and particle Stokes number on vortex shedding and particle clustering occurring in the flow. Flow over the cylinder is carried out using fully coupled Direct Numerical Simulations (DNS). Here, the point-particle approach is used for the suspended phase and the particle collisions are assumed to be perfectly elastic in nature. The vortex structures are identified by the Q-criterion and voronoi tessellation is employed to study the particle clustering in the flow. The effect of bluff body induced vortex separation over particle dispersion will be discussed. |
Sunday, November 24, 2024 8:26AM - 8:39AM |
A22.00003: Sediment transport on rippled beds. Octavio Guevara, Liheng Guan, Nadim Zgheib, Jorge S Salinas, S Balachandar We conduct an Euler-Lagrange, direct numerical simulation of a turbulent channel flow at a shear Reynolds number of $Re_{\tau}=180$ over an erodible particle bed. |
Sunday, November 24, 2024 8:39AM - 8:52AM |
A22.00004: Flocculation and Settling of Clay from a Radially Spreading Intrusion in a Two-Layer Fluid Diego Martinez Oritz, Bruce R Sutherland In the process of deep-sea mining, poly-metallic nodules on the ocean abyssal floor are carried to the surface along with bottom sediments. After the nodules are extracted, the sediments are re-injected into the ocean at depth. This motivates the present study of how a mixture of clay and water injected vertically into the stratified fluid spreads laterally at its neutral buoyancy level and how the clay eventually descends from this intrusion. Laboratory experiments are performed in which a mixture of clay and fresh water is injected downwards into a two-layer salt-stratified fluid. From side and top view movies, we measure the radial spread rate of the intrusion and settling speed of the particles. The intrusion spreads radially with faster speed if the source density is larger until the settling of particles below the intrusion begins, at which point the advance slows. The time at which settling below the intrusion begins decreases with increasing source density, with the settling speed being much larger than that predicted for individual clay particles as a result of flocculation. |
Sunday, November 24, 2024 8:52AM - 9:05AM |
A22.00005: Novel Apparatus for Studying Low Gravity Particle Dynamics in Multiphase Flow Ryan T Lewis, Tim Berk Dust is a major concern for NASA Lunar and Martian missions due to its abrasive nature and tendency to cover equipment. However, little is known about how dust behaves in low gravity environments. In this presentation we discuss the development of an apparatus that will simulate low gravity by placing electrostatically charged monosized particles in an upward electric field. This upward electric field creates an upward Coulomb forces that results in a simulated low gravity. Achieving a maximum surface charge on the particle stream is key to ensuring that all particles experience the same upward Coulomb forces and thus all particles simulate the same gravity. This presentation discusses the methodology, tests, and results of charging a particle stream using corona discharge and measuring the Coulomb forces that the charge particle stream experiences when placed in an electric field with a known strength. Future work will expand the platform to simulate low gravity in turbulent conditions. |
Sunday, November 24, 2024 9:05AM - 9:18AM |
A22.00006: Settling dynamics and interaction of mixed-density particle arrays in quiescent media Soohyeon Kang, Sophie Comer-Warner, Jim Best, Leonardo Chamorro We investigated the settling dynamics of particle arrays in water, with grains organized in a 10 by 10 pattern aligned in a horizontal plane. The experimental setup utilized spherical particles with a dimaeter of 4 mm and two different densities. Experiments were conducted in a 600 mm high tank with a cross-section of 300 mm by 300 mm. The particle array used a one-diameter spacing between adjacent particles, which were released simultaenously into the quiescent fluid medium. Various particle configurations were tested using particles with relative densities of 1.14 and 1.28 compared to water. The settling motions were captured using particle tracking velocimetry with three synchronized cameras, allowing us to determine the motions of the particles through triangulation during their settling to a depth of 40 particle diameters from their initial release position. Our observations revealed distinct dispersion patterns in mixed particle systems compared to homogeneous systems and dyanmics dependent on the relative particle arrangement. Characterization of the induced flow via stereo-particle image velocimetry provides additional insight into particle interactions and their settling behaviour. |
Sunday, November 24, 2024 9:18AM - 9:31AM |
A22.00007: Using microgravity to disentangle particle transport at the surface of an externally vibrated fluid Natalie Violetta Frank, Facundo Cabrera-Booman, Karl Cardin, Jeremie Auzoux, Andrew Wollman, Chris Rogers, Raúl Bayoán Cal Particle transport in a fluid is a rich phenomenon that involves a wide range of parameters. Characterization of such flows are crucial for understanding clustering and dispersion of microplastics or algae blooms in oceans and lakes. At the surface of a fluid, particle movement is driven by capillary immersion forces and capillary flotation forces. These interactions are entangled by the presence of gravity and are influenced by various characteristics such as particle size, surface tension, wettability, particle density, fluid wave length, and wave amplitude. The work presented here focuses on the influence of wave and particle characteristics on particle transport in microgravity conditions. Microgravity experiments aim to disentangle the dynamics of particle transport at the surface, isolating immersion forces on the particles. An open cylindrical container is placed on a wave driver, providing external harmonic forcing, and microparticles are placed at the surface of the fluid. Particle tracking is achieved through camera imaging from above for different wave frequencies and wave amplitudes. Experimental results presented are from drop tower experiments at Portland State University and compared to 1g control tests. Future work on the subject will be sent to the International Space Station for extended zero-gravity experimentation time. |
Sunday, November 24, 2024 9:31AM - 9:44AM |
A22.00008: Particle geometry effects on clustering dynamics: a study by primary school scientists Natalie Violetta Frank, Karl Cardin, William Ruehle, Ío Cal Fornier, Charlie Peters, Gemma Axline, Maria J Caballero, Raúl Bayoán Cal Microplastic pollution, algae growth, and pollen deposition are natural examples of particle-laden fluid surfaces. Dynamics of these particles can be further complicated by the presence of waves, which is often the case in these natural settings. Two types of forces influence the movement of these particles, and the tendencies to cluster; capillary flotation forces, and capillary immersion forces. The former is due to gravity, and the latter force is dictated by the particle's wettability. The work discussed here is a collaborative effort between Portland State University (PSU) and The Portland Montessori School (TPMS) investigating the effect of particle size and shape on the clustering dynamics at the surface of an externally vibrating fluid. Students from TPMS were introduced to the fundamental fluid dynamic lessons that build the foundation for particle-laden fluid surface studies by PSU students. Motivation behind why PSU studies particle-laden fluid was shared with TPMS students. TPMS students concluded this instructional period by designing and performing particle-laden fluid experiments of their own, focusing on different particle sizes, shapes, wave frequencies and amplitudes. Analysis was performed by PSU with particle tracking software. The discussion of results was led by the observations of TPMS students aided by PSU. |
Sunday, November 24, 2024 9:44AM - 9:57AM |
A22.00009: Post-Landing Firebrand Dynamics in Topography-Driven Turbulence Iago Dal-Ri dos Santos, Neda Yaghoobian During wildfires, a substantial number of smoldering particles, referred to as firebrands, are produced and carried downwind by the wind. Once landed, they can ignite secondary fires even several kilometers ahead of the main fire front. This phenomenon, known as spotting, can amplify the rate at which wildfires propagate, thereby increasing the vulnerability of wildlife and communities, and reducing the effectiveness of fire suppression efforts. |
Sunday, November 24, 2024 9:57AM - 10:10AM |
A22.00010: Inference of forcing kernels from limited observations in particle cloud tracers Nicolas Escobar-Castaneda, Qi Wang, Gustaaf B Jacobs Understanding the forcing law in particle-laden flows is crucial for accurately predicting and controlling these flows, especially under extreme conditions such as shock waves. Challenges arise when only limited statistical data for a group of particles is available for inferring the forcing law. Traditional predictive modeling approaches rely heavily on model assumptions with empirical parameters and lack the capability for uncertainty quantification. To address this issue, we developed an adjoint-based optimization framework built upon the closed Subgrid Particle-Averaged Reynolds Stress Equivalent (SPARSE) model. This framework infers the forcing law from the cloud location and covariance at the final time. The discrete adjoint operator functions provide an accurate gradient of the cost function with respect to the forcing law, which is then used for cost minimization. We applied this framework to a one-dimensional shock-particle interaction and to passive particles in a two-dimensional flow around a circular cylinder. Using this approach, we successfully reconstructed the forcing law, enabling accurate reproduction of observations. The results also demonstrate the impact of different modes within the forcing law on the resulting particle flow map. |
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