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 J26: Geophysical Fluid Dynamics: Atmospheric I |
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Chair: Marc Calaf, University of Utah Room: 251 D |
Sunday, November 24, 2024 5:50PM - 6:03PM |
J26.00001: Three-dimensional flow structure and ventilation dynamics of a cross-ventilated building Andrew J Banko, Tuhin Bandopadhyay, Brad P Sutton, Laura Villafane We present measurements of the three-dimensional flow structure and mixing dynamics for a cross-ventilated building model. The geometry consists of a cuboid building adapted from the wind tunnel study by Tominaga and Blocken (2015) with windward and leeward windows and a simple open interior. Comparisons are also made to a solid building with the same exterior dimensions. Experiments are conducted in a small-scale water channel facility at a fully turbulent building Reynolds number of 8,000. Kinematic similarity with high Reynolds number studies is maintained by enforcing the ratio of the building ventilation time scale to the characteristic advection time scale. A passive scalar contaminant is released upstream of the building for steady and transient release profiles. The three-dimensional velocity field is measured using magnetic resonance imaging and the time-resolved concentration field on the building center plane is measured using planar laser induced fluorescence. Together, these datasets provide two independent measurements of the building ventilation rate to validate the scaling methodology, and comparisons to high Reynolds number wind tunnel data demonstrate the efficacy of the low Reynolds number water channel, as long as the flow is fully turbulent and kinematic similarity is achieved. The results show that the building ventilation prolongs the plume residence time in the wake relative to the unventilated solid building case. Additionally, the spatially-averaged interior concentration is in good agreement with well-mixed arguments, yet zonal measures of interior fluctuations can be significant and are correlated to the cross-ventilation flow structure. Overall, these data elucidate the complex flow structure and unsteady plume dynamics around and within the building. |
Sunday, November 24, 2024 6:03PM - 6:16PM |
J26.00002: Eulerian and Lagrangian Analysis of Dispersion in an Idealized Urban Geometry Pau Fradera-Soler, Perry L Johnson, Andrew J Banko, S. Balachandar Understanding and modeling atmospheric dispersion in urban settings is important for air quality management and emergency response to harmful releases. In addition to prevailing winds and turbulent mixing, building-induced mean flow deflections play a significant role in the fate of dispersing plumes. In this study, Large-Eddy Simulations (LES) of scalar dispersion around an idealized cubical building demonstrate that the overturning motion of the horseshoe vortex inverts the crosswind position of the plume, so that fluid particles reaching the wake region directly behind the cube are more likely to come from upstream locations farther from the center plane of the cube. In addition to the Eulerian analysis of a continuous release, a Lagrangian analysis approach is implemented for efficient numerical access to two-point, two-time, and backward-in-time statistics that are difficult to compute via Eulerian methods. Formally, the probability distribution of Lagrangian particle positions, which is equivalent to the Green's function of the advection diffusion equation, is computed from particle trajectories and used to characterize the spatio-temporal characteristics of the plume. The simulations provide a detailed characterization of scalar dispersion and its relation to flow structures for both continuous and time-dependent releases. |
Sunday, November 24, 2024 6:16PM - 6:29PM |
J26.00003: Data-driven multiscale modeling of flow in plant canopies Marco G Giometto, Jacob Fish, Ensheng Weng, Jaeyoung Jung, David Lawrence The interaction of airflow with plant canopies governs the exchanges of heat, moisture, and gases between the canopy and the atmosphere, influencing local weather and climate variability. Accurately capturing these interactions numerically remains challenging, even with high-fidelity models like large-eddy simulation. This limits our ability to develop improved surface-flux parameterizations for weather and climate models, which currently depend on several phenomenological assumptions that are often invalid. In this study, we explore the viability of physics-data-driven multiscale techniques based on volume-averaging to represent such a process. A novel multiscale framework for the large-eddy simulation of flow in realistic plant canopies is proposed, based on the volume-averaged Navier-Stokes equations. Resolvable terms account for spatial variations in porosity in the canopy and are discretized numerically using a finite volume multi-resolution WENO scheme. To obtain subgrid-scale fluxes, we rely on a data-driven approach. To build subgrid-scale terms, a large database of so-called unit-cell problems is first considered where the interaction between canopy elements and the airflow is resolved via a sharp interface immersed boundary method and a large-eddy simulation closure. A data-driven surrogate of the unit-cell problem is then formulated and used as a closure model for the evaluation of subgrid-scale fluxes and canopy drag in the resolved-scale model. Predictions from the proposed formulation are validated against the reference solutions from fine-resolution simulations of flow over a realistic plant canopy environment and compared with alternative state-of-the-art techniques. |
Sunday, November 24, 2024 6:29PM - 6:42PM |
J26.00004: Unfolding The Link between Forest Canopy Structure and Flow Morphology Giulia Salmaso, Giulia Salmaso, Raúl Bayoán B Cal, Marc Calaf Turbulent flows over horizontally homogenous rough surfaces have long been studied, and they are categorized as rough-wall boundary layer flows. On the other hand, flows over homogeneously distributed bluff elements (e.g., homogenous forests) are typically described through a mix of rough-wall boundary layer and mixing-layer theory. However, most vegetated canopies are not homogenously distributed but instead are plagued with gaps and spatial heterogeneities of different scales. In these cases, it still remains unclear what the dominant flow traits are and how spatial heterogeneity affects them. Therefore, this project aims to characterize flows over vegetated canopies with scales of spatial heterogeneity ~ Ο (<span style="font-size:10.8333px">102) m, with a uniform under-canopy roughness and neutral stratification. |
Sunday, November 24, 2024 6:42PM - 6:55PM |
J26.00005: A statistical model for ice growth in the bulk region of mixed-phase clouds. Grigory Sarnitsky, Gaetano Sardina, Gunilla Svensson, Alain Pumir, Fabian Hoffmann, Bernhard Mehlig Mixed-phase clouds, responsible for most planet precipitations, are three-phase atmospheric systems containing ice, supercooled droplets, and water vapor. |
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