Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session J23: Convection and BuoyancyDriven Flows: General II 
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Chair: Chunendra Sahu, IIT Kanpur Room: 149AB 
Sunday, November 19, 2023 4:35PM  4:48PM 
J23.00001: Analog rain experiment: plumes of soluble particles Yutong CUI, Philippe Claudin, BENOIT SEMIN Rain is a critical component of the climate system. A key ingredient of the rain process is the coupling between flow and phase change. We investigate the sedimentation of a suspension of soluble solid particles from a localized point at the top of a water tank, serving as an analog for rain processes. Here, the air in the atmosphere is simulated by water in the tank, and the phase change between rain droplets and water vapor is represented by the dissolution of salt particles in water. 
Sunday, November 19, 2023 4:48PM  5:01PM Author not Attending 
J23.00002: Abstract Withdrawn

Sunday, November 19, 2023 5:01PM  5:14PM 
J23.00003: Diffusive and convective dissolution of carbon dioxide in a vertical cylindrical cel Daniël P Faasen, Farzan Sepahi, Dominik Krug, Roberto Verzicco, Pablo Peñas, Detlef Lohse, Devaraj van der Meer

Sunday, November 19, 2023 5:14PM  5:27PM 
J23.00004: Unifying heat transport model for the transition between buoyancydominated and Lorentzforcedominated regimes in quasistatic magnetoconvection Moritz Linkmann, Andrei Teimurazov, Matthew McCormack, Olga Shishkina In magnetoconvection, the flow is driven by buoyancy and Lorentz forces that distort the convective flow structure in the presence of a magnetic field. The different flow structures in the buoyancydominated and Lorentzforcedominated regimes lead to different heat transport properties in these regimes, reflected in distinct scaling relations of the total heat flux versus the strength of buoyancy and electromagnetic forces. Here, we propose a theoretical model for the transition between these two regimes for the case of a quasistatic vertical magnetic field applied to a convective fluid layer confined between two isothermal, a lower warmer and an upper colder, horizontal surfaces. We derive the relation between the scaling exponents in these two regimes and also the scaling of the onset of the transition. The theory is supported by our DNS and data from the literature. 
Sunday, November 19, 2023 5:27PM  5:40PM 
J23.00005: Early development of buoyant convection in porous media Chunendra K Sahu, Sibasish Panda Vertical buoyancydriven flows are usually termed as plumes. In porous media, plumes form when there is density gradient between two or more fluids, for example during groundwater contamination or carbon sequestration. Plumes have been studied theoretically to a large extent, but its evolution has not properly been analysed experimentally. Most studies in literature have focused on longterm behaviour assuming the plume to be fully developed. However, early time evolution of plumes is different from that in late times as the flow here is influenced equally by the transverse and longitudinal components of velocity and concentrations. We present light attenuation based table top experiments investigating the early development of plumes by changing the permeability of the medium and the density and flow rate of injection. We find that plumes initially form a blob shape, slowly turn into 'slightly elongated' and then eventually into 'fully elongated' shape. We quantify the time scales of transitions from one shape to the other as functions of the experimental variables. We also measure the length and volume of the plumes and find that they evolve as a power law on time. 
Sunday, November 19, 2023 5:40PM  5:53PM 
J23.00006: Thermal and compositional driven convection in thin reaction fronts Desiderio A Vasquez, Johann Quenta Chemical reaction fronts separate regions of reacted and unreacted substances as they propagate in liquids. These fronts may induced density gradients due to different chemical compositions and temperatures across the front. In this work, we investigate buoyancy induced convection driven by both types of gradients. We consider a thin front approximation where the normal front velocity depends only on the front curvature. This model applies for small curvature fronts independent of the specific type of chemical reaction. For density changes due only to heat variations near the front, we find that convection can take place for either upward or downward propagating fronts, if density gradients are above a threshold. Convection can set in even if the fluid with lower density is above the higher density fluid. Our model consists of the NavierStokes equations coupled to the front propagation equation. We carry out a linear stability analysis to determine the parameters for the onset of convection. We study the nonlinear front propagation for liquids confined in narrow twodimensional domains. Convection leads to fronts of steady shape propagating with constant velocities. 
Sunday, November 19, 2023 5:53PM  6:06PM 
J23.00007: Assessment of wallmodeling approaches for large eddy simulations of natural convection Lise Ceresiat, Miltiadis V Papalexandris Simulations of turbulent natural convection at high Rayleigh numbers are computationally very expensive due to gridresolution requirements, especially in the nearboundary regions where hydrodynamic and thermal boundary layers are developed. For this reason, it is common to resort to WallModeled Large Eddy Simulations (WMLES), according to which the turbulent scales in the inner layers are modeled and not resolved. This allows to reduce the number of grid points in the nearboundary regions, which offers significant computational savings. In this talk, we present WMLES of RayleighBénard convection at different Rayleigh numbers that involve modeling both the hydrodynamic and thermal boundarylayer structures. In particular, different wallmodeling approaches for the temperature field are discussed and their predictions are compared. Additionally, we address the issue of the modeling of the thermal boundary layer at freeslip boundaries such as, for example, the free surface of a liquid. To this end, we examine different approaches and assess their efficacy via comparisons of their predictions with those of wallresolved simulations of turbulent natural convection in an open cavity. 
Sunday, November 19, 2023 6:06PM  6:19PM 
J23.00008: Transition from rotation to buoyancy dominated regime in rotating RayleighBénard convection Jiaxing Song, Veeraraghavan Kannan, Olga Shishkina, Xiaojue Zhu The transition process from rotationdominated to buoyancydominated regime in rotating RayleighBénard convection is investigated via direct numerical simulation, with laterally periodic domains of both noslip and freeslip top and bottom boundary conditions. The comprehensive transition pathways from rotationally dominated to the buoyancydominated flows are realized by increasing the thermal deriving force (Rayleigh number, Ra) over five orders of magnitude, i.e. 10^{6}≤Ra≤10^{11} for one decade of Ekman number 10^{6} ≤Ek≤10^{5 }with the Prandtl number Pr=1. During the transition, the horizontal and vertical convective length scales display different scaling relations in rotationdominated and buoyancydominated regimes. A local Rossby number defined by combining these two different length scales is demonstrated to well quantify the transition point between the two flow regimes. Moreover, this local Rossby number is shown to match well with the transition between the thermal and viscous Ekman boundary layer (BL) thicknesses. The heat and momentum transport scaling relations during the transition are examined and agree well with the recent unifying transition scaling theory proposed based on the balance of the thermal and viscous Ekman BL thicknesses (Ecke & Shishkina, Annu. Rev. Fluid Mech. 55 (2023)). Instead of using the BL thickness, we extend the transition scaling theory based on the convective length scale, which is applicable to both noslip and freeslip boundary conditions. 
Sunday, November 19, 2023 6:19PM  6:32PM 
J23.00009: An energetically consistent Rayleigh number to characterise heterogeneous thermal forcing based on available potential energy. John Craske, Giovanni Fantuzzi, Ali Arslan, Andrew Wynn Studies of convection involving spatially heterogeneous heating and cooling typically adopt ad hoc definitions of the Rayleigh number by postulating length and temperature scales to characterise destabilising effects. Such definitions are problematic for making consistent comparisons and do not always have a welldefined physical justification. We therefore propose a precise definition of the Rayleigh number that has a consistent physical meaning across a range of problems involving spatially heterogeneous heating and cooling. The definition is based on a proxy for the supply of available potential energy, where the latter is positive semidefinite by construction and quantifies the provision of potential energy that can theoretically be converted into kinetic energy. The definition is therefore able to quantify the extent to which an arbitrary spatial distribution of heating or cooling is likely to be `destabilising'. We apply the definition to a wide range of examples and demonstrate that it extends naturally to a general formulation of such problems involving heating and cooling that is specified as a joint probability distribution in space and/or time. Along the way we clarify the connection between the concept of available potential energy and problems in optimal transport. 
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