Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session A17: Flow Instability: Multiphase Flow & Rayleigh-Taylor |
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Chair: Pedro Saenz, University of North Carolina at Chapel Hill Room: 145 |
Sunday, November 20, 2022 8:00AM - 8:13AM |
A17.00001: Dynamics of multilayer Rayleigh-Taylor mixing at moderately high Atwood numbers: an experimental study using simultaneous PIV-PLIF Devesh Ranjan, Prasoon Suchandra Statistically stationary gas tunnel experiments are performed to study multilayer Rayleigh-Taylor instability (RTI). Mixing between three gas streams are studied where the top and bottom streams comprise of air, and the middle stream is air-helium mixture. Experiments are at two Atwood numbers 0.3 and 0.6. We find the late-time mixing width to grow linearly. Dynamics of the flow is investigated using simultaneous particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF). Measures of molecular mixing indicate very high degree of molecular mixing at late times. Vertical turbulent mass flux a_y is calculated and in addition to its negative values for buoyancy-affected flows, we observe positive values of a_y due to entrainment at the lower edge of the mixing region. Scaling analysis suggests that vertical turbulent mass flux scales better with mixing width growth rate than vertical velocity fluctuations. It's found that majority of potential energy released has been dissipated due to viscous effects, and a mixing efficiency ~ 60% is observed. These experiments are of immense significance for atmospheric-oceanic flows, and for developing and validating turbulence models. |
Sunday, November 20, 2022 8:13AM - 8:26AM |
A17.00002: The onset and saturation of the Faraday instability in miscible fluids in a rotating environment Narinder Singh, Anikesh Pal We investigate the influence of rotation on the onset and saturation of the Faraday instability in a two-layer miscible fluid using a theoretical model and direct numerical simulations (DNS). Our analytical approach utilizes the Floquet analysis to solve a set of the Mathieu equations obtained from the linear stability analysis. The solution of the Mathieu equations comprises stable and harmonic, and sub-harmonic unstable regions in a three-dimensional stability diagram. We find that the Coriolis force stabilizes the flow and delays the onset of the sub-harmonic instability responsible for turbulent mixing at lower forcing amplitudes. However, the influence of rotation is small at higher forcing amplitudes. These results are corroborated by DNS at different Coriolis frequencies and forcing amplitudes. We also observe that for (f/ω)2<0.25, where f is the Coriolis frequency, and ω is the forcing frequency, the instability, and the turbulent mixing zone size-L saturates. When (f/ω)2≥0.25, the turbulent mixing zone size-L never saturates and continues to grow. |
Sunday, November 20, 2022 8:26AM - 8:39AM |
A17.00003: Spontaneous symmetry-breaking meniscus streaming Jian Hui Guan, Connor W Magoon, Matthew Durey, Roberto Camassa, Pedro Saenz When a fluid bath is vibrated vertically beyond a critical driving acceleration, the free surface destabilizes into a field of subharmonic standing waves, the so-called Faraday waves. A further increase in forcing gives rise to a secondary instability in which the standing Faraday pattern spontaneously becomes chaotic. When the bath is large relative to the characteristic wavelength, the waves form elongated patterns that appear, drift and disappear randomly on the free surface. Drawing inspiration from active-matter systems, we demonstrate that these out-of-equilibrium waves can spontaneously lead to coherent directed motion under confinement. In particular, chaotic Faraday waves may spontaneously develop into fast-moving travelling waves in either clockwise or anti-clockwise directions in annular geometries. Combining experiments and simulations, we rationalize the mechanism responsible for this instability in terms of the streaming flows generated near the vertical walls, which are critically enhanced by the meniscus. Moreover, we demonstrate how this instability can be harnessed for a range of applications in flow transport, mixing and particle sorting, and discuss the potential of these out-of-equilibrium waves as a platform to investigate new types of active meta-materials. |
Sunday, November 20, 2022 8:39AM - 8:52AM |
A17.00004: Compressible Rayleigh-Taylor Instability with Local Heat Transfer and Large Transport Property Contrasts Kevin Cherng, Sanjiva K Lele, Daniel Livescu In extreme environments such as during Inertial Confinement Fusion (ICF) or supernovae explosions, the Rayleigh-Taylor (RT) instability may occur under large variations in density or fluid transport properties, either through temperature variation or differences in the fluid properties themselves. We conduct DNS-quality simulations of the 3D fully compressible RT instability at various temperature ratios and transport property configurations, providing a more comprehensive overview of how heat conduction, large variations in transport properties and sudden changes in transport properties can affect the evolution of a RT mixing layer. We consider the idealized configuration of a hotter, less dense fluid pushing against a colder, denser fluid. Nonuniform fluid expansion/contraction induced by heat transfer can significantly affect local density differences and instability growth, causing profile asymmetries about the interface for flow and mixing statistics. We observe departure from self-similar development of the mixing layer, along with misalignment between regions of mixing and regions of most intense turbulent activity, caused by both heat transfer and transport property contrasts. |
Sunday, November 20, 2022 8:52AM - 9:05AM |
A17.00005: Kinetic effects on Rayleigh-Taylor instability Swapnil Majumder, Daniel Livescu, Sharath S Girimaji Rayleigh-Taylor instability (RTI) is important in a variety of flows, including inertial confinement fusion (ICF). During the coasting stage of ICF, RTI develops between the hot spot and colder surrounding plasma, due to the large temperature and density difference. RTI plays a significant role in the loss of compression and target performance in ICF. In the present study, we investigate non-equilibrium effects on the growth of RTI, using a gas-kinetic method with a modified flux reconstruction procedure, for a more accurate implementation of acceleration effects. We perform high-resolution simulations of RTI, for different parameter regimes. Characteristics of mixing layer fronts on the heavy and light fluid sides and changes compared to the continuum limit are studied under the effects of non-equilibrium thermodynamics. Further investigation of the departures from the Navier-Stokes limit are done using detailed turbulence diagnostics. |
Sunday, November 20, 2022 9:05AM - 9:18AM |
A17.00006: Large-eddy simulation and Reynolds-averaged Navier-Stokes modeling of three Rayleigh-Taylor mixing configurations with gravity reversal Brandon E Morgan High-fidelity large-eddy simulation (LES) is performed of Rayleigh-Taylor (RT) mixing in three different configurations involving gravity reversal. In each configuration, LES results are compared with one-dimensional Reynolds-Averaged Navier-Stokes (RANS) results, and a deficiency in a commonly used transport equation for the mass-flux velocity, aj, is identified. In the first configuration, a classical two-component RT mixing layer is allowed to develop before it is subjected to rapid acceleration reversal. In the second configuration, a three-component RT mixing layer with an intermediate density layer is allowed to develop before being subjected to rapid acceleration reversal. Finally, in the third configuration, a light layer is interposed between two heavy layers; in this configuration, only one interface is RT-unstable at a time as it undergoes rapid acceleration reversal. In all cases, a commonly used buoyancy production closure in the aj transport equation is shown to lead to significant over-prediction of mixing layer growth after gravity reversal. An alternative formulation for this closure is then presented which is shown to more accurately capture the stabilization effect of gravity reversal. |
Sunday, November 20, 2022 9:18AM - 9:31AM |
A17.00007: Growing elastomeric stalactites on different substrate morphologies Barath Venkateswaran, Trevor J Jones, Pierre-Thomas Brun This work uses curable elastomers and the Rayleigh-Taylor (RT) instability to create stalactite-like structures. A thin film of elastomer is coated on a flat plate and is flipped to allow the formation of a lattice of drops on the underside of the plate. The drop separation on this plate is dictated by the RT instability. Once cured, this process is repeated to form another layer of elastomer, and so on. Elastomeric stalactites are observed as the number of coatings is increased. We also observed that from the second layer onwards, the structure seems to have two regimes - a uniform thin film regime and a pendant drop regime. This problem is studied both in a dynamic way, to look at the time dependence of the process and in a hydrostatic way, to look at the equilibrium profiles of stalactites formed. |
Sunday, November 20, 2022 9:31AM - 9:44AM |
A17.00008: A Posteriori Analysis of Closures in RANS Models of a Small Atwood Number, Transitional Rayleigh–Taylor Mixing Experiment Oleg Schilling, Nicholas J Mueschke Profiles of closure models and of mean and turbulent transport equation budgets across the mixing layer obtained from direct numerical simulation data [O. Schilling and N. J. Mueschke, Physics of Fluids 22, 105102 (2010)] corresponding to a small Atwood number, transitional Rayleigh–Taylor mixing experiment performed in a water channel facility are compared to the profiles predicted by three- and four-equation mechanical–scalar Reynolds-averaged Navier–Stokes models at early-, intermediate-, and late-times. The models are initialized in several different ways, and both time-dependent and constant model coefficients are used. It is shown that the models provide very good predictions of the closure models used, as well as of the equation budgets. Comparisons to profiles obtained from analytical self-similar solutions valid in the Boussinesq limit are also presented. |
Sunday, November 20, 2022 9:44AM - 9:57AM |
A17.00009: Acceleration rate effects on Rayleigh-Taylor instability in elastic-plastic materials Aren Boyaci, Arindam Banerjee Rayleigh Taylor instability (RTI) is originally a hydrodynamic instability that can also occur in elastic-plastic (EP) materials. The majority of theoretical and numerical studies on RTI in EP materials assume a uniform and constant acceleration field. However, the applications of RTI in solids (i.e. inertial confinement fusion) occur at variable and impulsive acceleration fields. We have developed a rotating wheel experimental setup that allows for imposing variable acceleration profiles as well as adjustment of the rate of increase in the driving acceleration. In this setup, the test section filled with the soft material (mayonnaise) and air are attached to the disk in such a way that the centrifugal acceleration due to rotation acts on the soft material air interface perpendicularly. In our previous studies, the instability regime for both 2D and 3D initial perturbation geometries were addressed by our group under a linearly increasing driving acceleration. We will present results from our measurement campaign in which we evaluate the effects of the rate of increase in linear driving acceleration profiles for different regimes of RTI. The time evolutions of perturbation amplitude, perturbation mass, and axial stresses acting on the perturbation are analyzed to allow for a better understanding of RTI evolution and aid the development of more comprehensive models for RTI in EP materials. |
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