Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session S34: Flow Instability: General II |
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Chair: Jeane-Pierre Delplanque, UC Davis Room: 616 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S34.00001: Fragmenting a viscous cylindrical fluid filament using the Faraday instability Saswata Basak, Sagar Patankar, Ratul Dasgupta Faraday waves are nonlinear standing waves that appear on a liquid surface enclosed inside a vibrating container. A recent study by us (J. Fluid Mech. 2018, vol. 857, pp. 80$-$110.) has shown that the Mathieu equation governs the amplitude of small amplitude standing waves occuring on an inviscid cylindrical filament, when it is subjected to radial, pulsating body force. In the present study, we extend our linear stability analysis to a viscous cylindrical fluid filament using the toroidal-poloidal decomposition. We obtain the stability chart using numerical Floquet analysis. The stability curves are found not to touch the wavenumber (k) axis, when the viscosity of the fluid is taken into account, consistent with earlier observations by Kumar \& Tuckerman, J. Fluid Mech. 1994, vol. 279, pp. 49$-$68, Adou \& Tuckerman, J. Fluid Mech. 2016, vol. 805, pp. 591$-$610. in other geometries. The stabilisation of otherwise unstable Rayleigh$-$Plateau modes through forcing, is found to be extended in time for the viscous filament when compared to the inviscid one. We will show the possibility of fragmenting a filament using the Faraday mechanism and compare linearised predictions with Direct Numerical Simulations. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S34.00002: Reduced-order Models for Two-phase Annular Flows in Vertical Pipes Thomas Ewers, Alexander Wray, Omar Matar We study the dynamics of two-phase annular flow in vertical pipes. The conditions considered are such that there is no mass exchange between the phases due, for instance, to liquid entrainment into the gas, and bubble entrainment within the liquid. The gas is assumed to be turbulent, whilst the liquid phase exists in the form of a thin film adjacent to the wall. Reduced-order models are derived using asymptotic reduction for both axisymmetric and non-axisymmetric cases. The turbulence in the gas is modelled using a mixing length relation, while the method of weighted residuals is used in the film wherein inertial contributions are significant but the flow remains laminar. Numerical computations are carried out, which reveal the development of large-amplitude waves in the axisymmetric, and non-axisymmetric cases. Extensions to non-isothermal situations are outlined. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S34.00003: Analysis of Blast Driven Instability and Mixing from the Energetic Dispersal of a Perturbed Particle Bed Frederick Ouellet, Rahul Babu Koneru, Joshua Garno, S. Balachandar, Bertrand Rollin The evolution of particle clouds following interactions with a blast wave and contact interface resulting from detonating a high-energy explosive is a difficult problem for both numerical simulations and physical experiments. Experimentally, it is challenging to accurately characterize the initial states of both the explosive and the surrounding particle bed. Limitations also exist in the available diagnostic tools and measurable data which can be extracted from experiments. Thus, simulations can be a cheaper method to analyze the physics governing the interactions between the expanding particle cloud and the highly compressible, post-detonation fluid flow. Using multiphase, compressible flow simulations in an Eulerian-Lagrangian frame, the impact of perturbing a particle bed surrounding an explosive charge is analyzed. The analysis focuses on the multiphase instabilities and late-time behavior displayed by the dispersing particle cloud and discusses the associated underlying physical phenomena. Effects of the instabilities on the mixing behavior of the detonation products with the surrounding air are also discussed. The perturbations are varied to unravel the effects of the initial particle distribution and its persistence in the late time particle cloud and the background fluid flow. Inspired by work on two-fluid interfacial instabilities, this study relates to work in the emerging field of shock-driven multiphase instabilities but at extreme conditions and moderate initial particle loadings.~~~ [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S34.00004: On hydrodynamic instabilities in pseudo-boiling with supercritical fluids. Rebecca Barney, Robert Nourgaliev, Jean-Pierre Delplanque, Rose McCallen We investigate hydrodynamic instabilities arising in mixed forced and natural convection laminar flow at supercritical thermodynamic conditions. Fluid in this regime is compressible, with highly varying properties, even for vanishingly small Mach numbers. Hydrodynamic stability is influenced by the occurrence of pseudo-phase change near the channel wall, as defined by the peak of the specific heat above the critical point. While the fluid properties do not explicitly exhibit a discontinuous change, the steep continuous property changes create flow patterns which qualitatively look like boiling. Of interest is investigating this boiling-like phenomenon to characterize the heat transfer in the supercritical regime. Due to the highly-varying density and specific heat fields, we solve the fully compressible Navier-Stokes equations. An advanced equation of state for supercritical water was implemented in an Arbitrary Lagrangian-Eulerian multi-physics simulation tool developed at Lawrence Livermore National Laboratory. A newly developed, robust, 5$^{\mathrm{th}}$ order in both space and time, fully implicit, all-speed, reconstructed discontinuous Galerkin method is used to enable the numerical simulations. As the bottom wall is heated, the density decreases at the wall increasing the flow instabilities. The Richardson number indicates when the flow is dominated by forced or natural convection and provides a map/correlation between buoyancy effects and unstable flow features. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S34.00005: A new mechanism for the generation of interface distortions in liquid jets Hanul Hwang, Parviz Moin, M. J. Philipp Hack The onset of the atomization process of liquid jets is commonly understood as a sequence of exponential instabilities whose amplification eventually leads to a distortion of the interface and the breakup of the jet into droplets. Our study analyzes the amplification of interface perturbations of liquid jets through an optimization problem within a spatial linear framework. The objective functional is the interface potential energy due to surface tension. We demonstrate that a multi-phase Orr mechanism can serve as an alternative pathway for the generation of interface distortions by redistributing energy from the mean shear into perturbations of the jet surface. Parameter studies show that the amplification of interface disturbances scales with both Reynolds number and Weber number. Analysis of the budget of the perturbation kinetic energy provides further insight into the underlying physics. For high Weber numbers, the amplification of the surface distortion is bounded by viscous effects, whereas surface tension limits the growth in the case of low Weber numbers. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S34.00006: Squeezing to Bending Transitions of Interfacial Electrohydrodynamic Instabilities for Digitization and Mixing of Two-Phase Microflows Joydip Chaudhuri, Tapas Kumar Mandal, Dipankar Bandyopadhyay External field induced interfacial instabilities have shown significant potential in the miniaturization of flow patterns inside the microfluidic devices. Electric field induced instabilities in a trilayer oil-water microflow is explored with the help of analytical models and computational fluid dynamics simulations. Twin oil-water interfaces undergo either in-phase bending or anti-phase squeezing mode of deformation when a direct current (DC) electric field is applied locally. The selection of modes depends on the magnitudes of applied DC field intensity and oil-water interfacial tension. The growth of the squeezing mode leads to a time-periodic dripping of droplets at lower field intensities, whereas, bending mode develops into `whiplash' ejection of miniaturized droplets having octuplet microvortices inside and outside, at higher field intensities. A transition from purely laminar flow is observed during the switch over to bending mode, resembling von K\'{a}rm\'{a}n vortex street formation. Use of alternating current (AC) electric field with variation in frequency and waveform is also found to create on-demand and time-periodic array of flow features following the mode selection. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S34.00007: Phase transitions to condensate formation in two-dimensional turbulence Moritz Linkmann, Guido Boffetta, M. Cristina Marchetti, Bruno Eckhardt Two-dimensional (2d) and quasi-2d flows occur at macro- and mesoscale in a variety of physical systems. Examples include stratified layers in Earth's atmosphere and the ocean, soap films and more recently also dense bacterial suspensions, where the collective motion of microswimmers induces patterns of mesoscale vortices. A characteristic feature of 2d turbulence is the occurrence of an inverse energy cascade. In absence of large-scale friction the inverse energy cascade results in the formation of large-scale coherent structures, so-called condensates. We here study the formation of the condensate as a function of the kind and amplitude of the forcing. Direct numerical simulations show that the condensate appears in a phase transition. For prescribed energy dissipation the transition is second order; for active matter, where the forcing is due to a small-scale instability, the transition is first order. The phase transition separates two markedly different types of 2d dynamics: in turbulence with a condensate, energy input is mostly balanced by dissipation in the condensate and intermediate scales follow an inertial cascade; without a condensate dissipation is spread over the intermediate scales and the properties of the energy transfer are different and non-universal. [Preview Abstract] |
Tuesday, November 26, 2019 12:02PM - 12:15PM |
S34.00008: Emergence of Two Invariants from One in MHD Turbulence Hussein Aluie, Xin Bian In incompressible MHD flows, it is only total energy that is conserved and not magnetic or kinetic energy separately. As a manifestation of order emerging out of chaos (or permanence out of turbulence), we have found in [1] that they are in fact conserved separately over a range of scales in turbulent flows. This essentially gives us two global invariants (kinetic energy and magnetic energy) instead of just one (total energy). I will discuss this seemingly counter-intuitive result and how it is to be reconciled with the strong magnetic-flow coupling and the role of waves in MHD turbulence. I will put this result in the context of cascade theories and briefly examine its potential implications on the energetics and dissipation of plasma flows, magnetic reconnection, magnetic dynamos, and also on modeling efforts. [1]X. Bian and H. Aluie, Phys. Rev. Lett. 122, 135101 (2019). [Preview Abstract] |
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