Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session J41: Multiphase Flows: Modeling and Theory I 
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Chair: Andre Calado, George Washington University Room: 206 
Sunday, November 19, 2023 4:35PM  4:48PM 
J41.00001: Risk assessment using a fluidmechanics informed statistical framework for short and longterm exposure for indoor airborne viral transmission Krishnaprasad K A, Nadim Zgheib, Jorge Salinas, S Balachandar, M Y Ha, Kailash Choudhary The risk of airborne viral contagion in indoor spaces can be greatly mitigated or aggravated by the quality of the ventilation system. Theoretical models [1] have been used extensively to predict the spread of infectious diseases in such settings. This work is aimed at providing a statistical framework to act as an improvement on the wellmixed theory by leveraging LES and RANS simulations of fluid flow and droplet nuclei dispersal in multiple room and ventilation configurations. The developed framework provides a simple multiplicative correction factor, that accounts for the roles of separation distance and filtration efficiency, to quantify the deviation of the simulations from the theory [2,3]. 
Sunday, November 19, 2023 4:48PM  5:01PM 
J41.00002: Evaluation of a Subgrid Surface Dynamics Model for DualScale Modeling of Surface Tension Effects Dominic Kedelty, Marcus Herrmann Direct Numerical Simulation remains a prohibitively expensive task in Computational Fluid Dynamics, even more so for cases involving atomization. Instead of DNS, a dualscale modeling approach (Gorokhovski and Herrmann, 2008) that describes turbulent phase interface dynamics in a Large Eddy Simulation spatial filtering context is proposed. Spatial filtering of the equations of fluid motion introduce several subfilter terms that require modeling. Instead of developing individual closure models for the interface associated terms, the dualscale approach uses an exact closure by explicitly filtering a fully resolved realization of the phase interface. This resolved realization is maintained using a Refined Local Surface Grid approach (Herrmann, 2008) employing an unsplit geometric Volumeof Fluid method (Owkes and Desjardins, 2014). Advection of the phase interface on this DNS scale requires a reconstruction of the fully resolved interface velocity. In this work, adaptations for a SubGrid Surface Dynamics (SGSD) model (Herrmann 2013) are applied to the VOF context. The SGSD model creates velocities that are not divergencefree and therefore must be corrected with a projection/correction step as in the Fractional Step Method. Since divergencefree velocities are needed only in the direct proximity of the phase interface, one can restrict the projection/correction to a narrow band surrounding the interface. Several implementations involving the size and boundary conditions of the Poisson equation are explored. Various test cases such as the oscillation period and damping of a weakly deformed mode 2 drop, the behavior of a stable and unstable RayleighPlateau column, and viscous capillary break up of a ligament are used to evaluate the SGSD model. 
Sunday, November 19, 2023 5:01PM  5:14PM 
J41.00003: Volume of Fluid based study of the three phase dynamic contact line in the wetting of a thin channel. Yash KULKARNI, Tomas Fullana, Mathis Fricke, Stephane Popinet, Stephane Zaleski To investigate the threephase dynamic contact line in the wetting of thin channels, we numerically design a setup consisting of a pressure gradient driven twophase flow inside a thin pore (width ~ 3050 nm). The two phases are separated by an interfacial layer with surface tension, that meets the moving pore wall, hence, a threephase dynamic contact line is formed, whose modelling is a significant scientific challenge [1], [2]. This setup is then studied numerically by solving the 2D twophase NavierStokes equation subject to three contact line boundary conditions: The Navier slip boundary condition, the superslip boundary condition and the generalised Navier boundary condition (GNBC). We use the Basilisk flow solver to do VolumeofFluid method based simulations with the surface tension force computed using the Continuous surface force method and curvature calculation using the height function. Steady state solutions are found and a critical capillary number, based on the contact line velocity, is predicted beyond which no steadystate solution exists. We see that the Navier slip model with a constant microscopic contact angle is weakly singular, however, sufficient to predict the critical capillary number for wetting. A parametric study with nanometric slip length is done and scaling laws for the interface bending are discovered in the vicinity of the contact line. Then we study the problem using the superslip boundary condition and a novel VoF based implementation of the generalised Navier boundary condition GNBC. The results from these methods give direct evidence of more regularised solution in the vicinity of the contact line. 
Sunday, November 19, 2023 5:14PM  5:27PM Author not Attending 
J41.00004: Abstract Withdrawn

Sunday, November 19, 2023 5:27PM  5:40PM 
J41.00005: A FieldMonteCarlo framework for simulating nucleateboiling flows Lorenz Weber, Andreas G Class The accuracy of simulations using Reynoldsaveraged NavierStokes equations for boiling flows strongly depends on the correct modeling of the phase interaction, in particular the interfacial mass transfer. Different modeling approaches exist to address stochastic, nonlinear effects in bubbly or droplet flows. Such approaches feature various tuning parameters that require a priori knowledge of the flow. In this study, we utilize a FieldMonteCarlo method, in a fully Eulerian framework, in our implementation of a nucleateboiling flow simulation. The FieldMonteCarlo approach has been successfully applied to reacting flows as well as disperse twophase flows for cavitation and spray; however, it has not been applied to nucleateboiling flows. In this study, we implement the presented framework in a finitevolume environment, also combined with a secondorder stochastic RungeKutta scheme. Additionally, we discuss the relevant closure terms and the solver algorithm. The test case considered is a flow through a duct with a single heated wall. The obtained results are compared to (1) the results of a commercial stateoftheart model for boiling flows and (2) experimental results. Finally, we highlight the advantages of the presented approach. 
Sunday, November 19, 2023 5:40PM  5:53PM 
J41.00006: Hystereses in onedimensional compression of a poroelastic hydrogel Zelai Xu, Pengtao Yue, James J Feng We investigate theoretically the onedimensional compression of a hydrogel layer by a uniform fluid flow normal to the gel surface. The flow is driven by a pressure drop across the gel layer, which is modeled as a poroelastic medium. Since the pressure simultaneously drives the Darcy flow through the pores and compresses the gel, the fluxpressure relationship can become nonmonotonic. Most interestingly, we discover two types of hysteresis when either the pressure drop or the flux is controlled, which are also confirmed by transient numerical simulations. The hystereses stem from the interplay between the gel compression at the upstream interface and that in the bulk of the gel, and would not be predicted by models that ignore the interfacial compression. Finally, we suggest experimental setups and conditions to seek such hystereses in real gels. 
Sunday, November 19, 2023 5:53PM  6:06PM 
J41.00007: Volume oscillations slow down a rising Taylor bubble Guangzhao Zhou, Andrea Prosperetti Taylor bubbles  volumes of gas rising in vertical tubes with an equivalent spherical diameter greater than the diameter of the tube  are often encountered in the energy, chemical and oil industries. In a recent paper (Zhou & Prosperetti, J. Fluid Mech. 920, R2, 2021) we have shown that, artificially constraining the bubble diameter by means of a porous surface coaxial with the tube, the rising velocity of the bubble can be considerably increased. This result establishes a connection between the bubble rising velocity and the drainage liquid flow in the film separating the bubble from the tube wall. In the present work we find by numerical means that, if the bubble is forced to execute smallamplitude volume oscillations, subtle nonlinear processes involving liquid inertia and the displacement of stagnation points on the bubble surface cause the liquid film to become considerably thinner than for an ordinary constantvolume Taylor bubble. Correspondingly, the bubble rise considerably slows down and very nearly stops. 
Sunday, November 19, 2023 6:06PM  6:19PM 
J41.00008: Effect of convergentshaped vessel on the velocity of impactinduced focused liquid jets Hiroya Watanabe, Kohei Yamagata, Yuto Yokoyama, Hiroaki Kusuno, Yoshiyuki Tagawa The impactinduced focused liquid jet technology can eject highviscosity liquids (up to about 8,000 mPa・s) with a simple mechanism. The generation of faster jets is expected to make it possible to use this technology in various fields, including industrial and medical fields. In this study, impactinduced liquid jet ejection experiments were conducted with two vessels to investigate the effect of vessel geometry on the jet velocity. We used a Kjeldahl flask, in which the twodimensional pressure distribution is not negligible, and a test tube used in previous studies, which has a simple cylindrical shape and is considered to have a onedimensional, linear pressure distribution. Remarkably, as a result, by using a Kjeldahl flask, we successfully generate jets with velocity about twice that of a test tube. To understand the results, the Laplace equation on the pressure impulse inside the vessel is solved numerically and analytically. The distribution of the pressure impulse showed consistent results with the jet velocity measured in experiments. Importantly, unlike the test tube with no crosssectional area change, a convergentshaped vessel has a stronger nonlinearity in the pressure impulse distribution, resulting in an increase in the liquid velocity at the gasliquid interface. 
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