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 T32: Particle Laden Convection |
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Chair: Andrew Grace, University of Notre Dame Room: 255 D |
Monday, November 25, 2024 4:45PM - 4:58PM |
T32.00001: Supersaturation and droplet growth statistics in turbulent moist convection: Applications for LES subgrid modeling Kamal Kant Chandrakar, Hugh Morrison, Raymond A Shaw Turbulent fluctuations of scalar fields are critical for cloud microphysical processes. Variability of supersaturation (a joint scalar of water vapor and temperature) can affect cloud droplet formation and droplet size distribution in turbulent clouds. This study investigates water vapor, temperature, supersaturation, and droplet statistics in DNS of moist Rayleigh-Bénard convection to provide a foundation for modeling subgrid-scale interactions in atmospheric models. |
Monday, November 25, 2024 4:58PM - 5:11PM |
T32.00002: Exploring the transition from condensation to coalescence growth in convective clouds and fogs Jacob Kuntzleman, Steven K Krueger, Raymond A Shaw Growth by aggregation or coalescence is fundamental to a multitude of natural and engineered processes, from the precipitation of colloids to the formation of planets. The rate at which droplets collide and coalesce to form precipitation is one of the fundamental controlling processes for cloud stability, lifetime, and optical properties. To explore the transition from cloud droplet growth by condensation to growth by coalescence, we take cloud formation in moist Rayleigh-Benard convection as a minimal model. We first explored the conditions favorable to collision-coalescence growth using a Monte Carlo model. Next we developed analytic expressions for the characteristics of the droplet size distribution that account for the onset of growth by coalescence. A dimensionless parameter emerges from the analysis, describing the functional form of the coalescence tail of the size distribution. This allows us to identify cloud conditions that are conducive to drizzle initiation. We conclude by extending the theory to atmospherically relevant conditions and by suggesting that the model may serve as the basis for a physically-based parameterization of drizzle formation in stratiform clouds and fogs. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T32.00003: The Settling Rates of Particles in Rayleigh–Bénard Turbulence Kristin Swartz-Schult, Jesse Charles Anderson, Hamed Fahandezh Sadi, Swafuva Varappillikudy Sulaiman, Will Cantrell, Raymond A Shaw, David H Richter, Andrew P Grace It is widely recognized that better understanding the interaction between clouds and aerosols is among the most pressing and essential endeavors in climate and atmospheric sciences. A particular process of interest is the settling rate of heavy particles and how it affects rain formation and droplet size distribution. While much work has been done to understand particle settling rates in homogeneous isotropic turbulence and the potential for particles to settle significantly faster than their predicted Stokes settling velocity, more work needs to be done in other environments. Towards this aim, a set of experiments was conducted utilizing the Pi Cloud Chamber experimental facility at Michigan Technological University to investigate the physics dictating particle settling time in Rayleigh-Bénard turbulence. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T32.00004: Particle-resolved simulations and dune formation in particulate Rayleigh-Bénard flow Xianyang Chen, Myoungkyu Lee, Daniel Floryan, Rodolfo Ostilla Monico, Andrea Prosperetti Fully resolved simulations of particulate Rayleigh-Bénard convection in a doubly periodic cell (aspect ratio Γ=2) with 20,000 particles at a volume fraction of 3.25% and a Rayleigh number of Ra = 108 have been conducted using 2.1 billion grid points and 600 NVIDIA V100 GPUs on DOE's Summit system. The particles are 10% heavier than the fluid and tend to settle. However, near the cell bottom, the velocity of the circulating fluid acquires a horizontal component which entrains them toward the root of rising plumes. The particles gradually accumulate at these sites forming dunes which strengthen the plumes. When the dunes are sufficiently large, other particles are dragged up their slope by the flow, acquire a vertical velocity component and are entrained by the rising fluid. Thus, particle resuspension ultimately depends on drag, rather than lift, forces. The simulations demonstrate a tendency for our system to form a single large, stable dune that perpetuates the process. Most particles in the large dune remain within it, stabilizing its structure and promoting the resuspension of other particles. Other transient smaller dunes also form, but are quickly eroded by the flow. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T32.00005: Laboratory experiments of particle-driven convection Gaël Kemp, Stuart B Dalziel, Megan Davies Wykes Particle-driven convection occurs when a dense particle-laden layer settles into a layer of clear fluid. This can drive a variation on the classical Rayleigh-Taylor instability, where particles induce the density difference between the two fluids. Variants of this instability occur in many geophysical flows, such as the undersides of volcanic ash clouds, sediment-laden river outflows, and the dynamics of droplets in clouds. This talk will present some new experimental results of Rayleigh-Taylor instability occurring between a particle-laden and fresh-water layers. We will also present some preliminary results that examine the effect of adding salt to the lower layer. For this second case, the initial stratification is stable, but becomes unstable due to particle settling. |
Monday, November 25, 2024 5:50PM - 6:03PM |
T32.00006: Time-resolved X-ray measurements of lock-exchange turbidity currents Parth Devrajbhai Khokhani, Elijah D Andrews, Jackson Lewis, Jackson Lewis, Harish Ganesh Turbidity currents are gravity-driven flows where a dense mixture of sediment and fluid moves into lighter ambient fluid due to density differences. These types of flows occur in oceans, avalanches, and volcanic flows. Experimental measurements of the spatiotemporal evolution of density fields during current propagation are essential to understanding mixing dynamics at different density ratios. This study uses time-resolved X-ray densitometry to investigate turbidity currents in a two-dimensional lock-release system. The experiments involve two sand particle sizes (60 microns and 120 microns), four water depths (25 mm to 100 mm), initial particle concentration ranging from 30 g/L to 490 g/L. The density ratio in the experiments varies from 0.77 to 0.98, encompassing both Boussinesq and non-Boussinesq limits. Acceleration, slumping, and deceleration phases of currents with different sand sizes and column heights are presented. X-ray densitometry-based evolution of density fields is discussed for the three phases and a range of density differences. The entrainment and evolution of the current head density profile are discussed from the time-resolved X-ray-based density field measurements. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T32.00007: The role of thermally evolving particles in Rayleigh-Bénard turbulent mixing Lee Rosenberg, Sarah Beetham Thermally-evolving, multiphase flows are prevalent across industrial and natural processes, such as nuclear and circulating fluidized bed reactors, desalination systems and complex macrobiological systems. Despite their societal importance, tractable models capable of accurately predicting global quantities of interest have remained elusive. This is in large part due to the complex nature of these systems and the challenge in producing high-fidelity data, either computationally or experimentally. In this talk, we quantify the role of a dispersed phase in thermally evolving channel flow. Here, the walls are vertically oriented and held at opposing temperatures (one hot and one cold). We discuss the convective behavior of this vertically oriented Rayleigh-Bénard system, absent of particles first, then make comparisons with an analogous system seeded with isothermal particles at sufficiently high mass loading such that heterogeneous effects, such as clustering are observed. Finally, we extend this configuration to allow the particles to also evolve thermally. This work uses an open source Euler-Lagrange framework (NGA2) to generate a high-fidelity data spanning a range of particle volume fractions and Rayleigh numbers. This data is then used to quantify the convective behavior and a new scaling law is proposed for the Nusselt number that takes into account not only the Rayleigh and Prandtl numbers, but also disperse phase properties, such as mass loading and volume fraction. |
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