Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S12: Turbulence and Multi-Phase Flows |
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Sponsoring Units: DFD GSNP Chair: Subash Sharma, Purdue University Room: 271 |
Thursday, March 16, 2017 11:15AM - 11:27AM |
S12.00001: Towards building a robust computational framework to simulate multi-physics problems - a solution technique for three-phase (gas-liquid-solid) interactions Lucy Zhang In this talk, we show a robust numerical framework to model and simulate gas-liquid-solid three-phase flows. The overall algorithm adopts a non-boundary-fitted approach that avoids frequent mesh-updating procedures by defining independent meshes and explicit interfacial points to represent each phase. In this framework, we couple the immersed finite element method (IFEM) and the connectivity-free front tracking (CFFT) method that model fluid-solid and gas-liquid interactions, respectively, for the three-phase models. The CFFT is used here to simulate gas-liquid multi-fluid flows that uses explicit interfacial points to represent the gas-liquid interface and for its easy handling of interface topology changes. Instead of defining different levels simultaneously as used in level sets, an indicator function naturally couples the two methods together to represent and track each of the three phases. Several 2-D and 3-D testing cases are performed to demonstrate the robustness and capability of the coupled numerical framework in dealing with complex three-phase problems, in particular free surfaces interacting with deformable solids. The solution technique offers accuracy and stability, which provides a means to simulate various engineering applications. [Preview Abstract] |
Thursday, March 16, 2017 11:27AM - 11:39AM |
S12.00002: Direct Numerical Simulations of Particle-Flow Interactions in a Channel Anand Samuel Jebakumar, Kannan Premnath, John Abraham Particle-laden flows are important in many energy applications including coal combustors, gasifiers and internal combustion engines. In a recent study, Lau and Nathan (2014) reported that particles in a turbulent pipe flow migrate preferentially either toward the axis or the wall depending on their Stokes number. They attribute this preferential migration to two forces: Saffman lift, which arises due to the mean velocity gradient across the particle, and turbophoretic force, which arises due to a gradient in the turbulent kinetic energy across the particle. In order to understand the interaction of particles with turbulence in a wall-bounded flow and the effect of these forces, we have performed Direct Numerical Simulations (DNS) of particle-flow interactions in turbulent channel flow. The Lattice Boltzmann Method (LBM) is employed for these DNS studies. The effects of particle size, Reynolds number, and Stokes number are considered in the analysis. The corresponding mean velocity and turbulent kinetic energy gradient as well as their effect on the force acting on the particle is examined. [Preview Abstract] |
Thursday, March 16, 2017 11:39AM - 11:51AM |
S12.00003: Liquid spray experiments Gary Lapham, John McHugh When waves on the ocean surface interact with a solid object, the result is often a complex pattern of spray. The solid object may be a coastal barrier such as a breakwater, or a ship or drilling rig. Another spray-related case is the presence of large industrial tanks of liquid, and often dangerous liquids, that exist around the world. Tens of thousands of such tanks are rapidly becoming obsolete. Recent experience has shown that when such tanks burst, the resulting spray may shoot several hundreds of meters from the tank. These tanks often have a wall or dam (barrier) surrounding them in an attempt to contain any leakage, catastrophic or otherwise. When the tank bursts it is akin to the dam-break problem. A “wall” of water rushes forth and impinges on the barrier creating spray. Previous experiments (McHugh and Watt, 1998) considered the related configuration of a solitary wave impinging on a vertical wall. The present experiments more closely model the bursting tank case, and treat the effect of the distance between the tank and barrier. Results show that there is a “sweet spot” where height and horizontal distance of spray droplets are maximized. This ideal distance between tank and barrier is constant when scaled by the initial tank depth. [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:03PM |
S12.00004: Inertial focusing in microchannel with triangular cross-section and size-based particle separation Jeong-ah Kim, Wonhee Lee Inertial microfluidics is widely used for biological and chemical applications where high-throughput passive microparticle handling is required. We previously proved that cross-section shape can be a control parameter. We investigated inertial focusing in triangular channels with various sizes and angles while varying particle size and Reynolds number. Previous study reported 3 focusing positions close to center of each channel face. We found unexpected focusing behavior, which is the alteration of focusing configuration depending on particle size and Re. We fabricated a micro channel with varying cross-section along flow direction to control accessible focusing positions, by which enabled elimination of the overlapped focusing positions. The resulting channel allows particles with different size to focus at completely different focusing positions in a triangular channel, which leads to highly efficient particle separation without the external forces or labeling. [Preview Abstract] |
Thursday, March 16, 2017 12:03PM - 12:15PM |
S12.00005: A Well-Posed, Objective and Dynamic Two-Fluid Model. Krishna Chetty, Avinash Vaidheeswaran, Subash Sharma, Alejandro Clausse, Martin Lopez de Bertodano The transition from dispersed to clustered bubbly flows due to wake entrainment is analyzed with a well-posed and objective one-dimensional (1-D) Two-Fluid Model, derived from variational principles. Modeling the wake entrainment force using the variational technique requires formulation of the inertial coupling coefficient, which defines the kinetic coupling between the phases. The kinetic coupling between a pair of bubbles and the liquid is obtained from potential flow over two-spheres and the results are validated by comparing the virtual mass coefficients with existing literature. The two-body interaction kinetic coupling is then extended to a lumped parameter model for viscous flow over two cylindrical bubbles, to get the Two-Fluid Model for wake entrainment. Linear stability analyses comprising the characteristics and the dispersion relation and non-linear numerical simulations are performed with the 1-D variational Two-Fluid Model to demonstrate the wake entrainment instability leading to clustering of bubbles. Finally, the wavelengths, amplitudes and propagation velocities of the void waves from non-linear simulations are compared with the experimental data. [Preview Abstract] |
Thursday, March 16, 2017 12:15PM - 12:27PM |
S12.00006: Linear Instability Analysis of non-uniform Bubbly Mixing layer with Two-Fluid model. Subash Sharma, Krishna Chetty, Martin Lopez de Bertodano We examine the inviscid instability of a non-uniform adiabatic bubbly shear layer with a Two-Fluid model. The Two-Fluid model is made well-posed with the closure relations for interfacial forces (Bertodano et al. 2016). First, a characteristic analysis is carried out to study the well posedness of the model over range of void fraction with interfacial forces for virtual mass, interfacial drag, interfacial pressure. A dispersion analysis then allow us to obtain growth rate and wavelength. Then, the well-posed two-fluid model is solved using CFD to validate the results obtained with the linear stability analysis. The effect of the void fraction and the distribution profile on stability is analyzed. [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 12:39PM |
S12.00007: Passive sorting of capsules by deformability Edgar Haener, Anne Juel We study passive sorting according to deformability of liquid-filled ovalbumin-alginate capsules. We present results for two sorting geometries: a straight channel with a half-cylindrical obstruction and a pinched flow fractioning device (PFF) adapted for use with capsules. In the half-cylinder device, the capsules deform as they encounter the obstruction, and travel around the half-cylinder. The distance from the capsule’s centre of mass to the surface of the half-cylinder depends on deformability, and separation between capsules of different deformability is amplified by diverging streamlines in the channel expansion downstream of the obstruction. We show experimentally that capsules can be sorted according to deformability with their downstream position depending on capillary number only, and we establish the sensitivity of the device to experimental variability. In the PFF device, particles are compressed against a wall using a strong pinching flow. We show that capsule deformation increases with the intensity of the pinching flow, but that the downstream capsule position is not set by deformation in the device. However, when using the PFF device like a T-Junction, we achieve improved sorting resolution compared to the half-cylinder device. [Preview Abstract] |
Thursday, March 16, 2017 12:39PM - 12:51PM |
S12.00008: Vortex rings : a probe for Turbulence ? Stephane Perrard, William T M Irvine How does a vortex ring evolve in a turbulent environment ? We investigate this question by performing a scattering experiment in which a vortex ring is shot through a turbulent background flow. We track the evolution of the vortex loop and the turbulent flow using either particle image velocimetry (PIV) or vorticity line tracking. I will present our observations of how the ring deforms and stretches as it wrestles with the background turbulence and discuss how this type of experiment could tell us more about the dynamical evolution of structures in a turbulent flow. [Preview Abstract] |
Thursday, March 16, 2017 12:51PM - 1:03PM |
S12.00009: Jets or vortices - what flows are generated by an inverse turbulent cascade? Anna Frishman, Jason Laurie, Gregory Falkovich An inverse cascade--energy transfer to progressively larger scales - is a salient feature of two-dimensional turbulence. If the cascade reaches the system scale, it creates a coherent flow expected to have the largest available scale and conform with the symmetries of the domain. In a doubly periodic rectangle, the mean flow with zero total momentum was therefore believed to be unidirectional, with two jets along the short side; while for an aspect ratio close to unity, a vortex dipole was expected. Using direct numerical simulations, we show that in fact neither the box symmetry is respected nor the largest scale is realized: the flow is never purely unidirectional since the inverse cascade produces coherent vortices, whose number and relative motion are determined by the aspect ratio. This spontaneous symmetry breaking is closely related to the hierarchy of averaging times. Long-time averaging restores translational invariance due to vortex wandering along one direction, and gives jets whose profile, however, can be deduced neither from the largest-available-scale argument, nor from the often employed maximum-entropy principle or quasi-linear approximation. [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S12.00010: Sparse sampling and asymptotical field averages in turbulence Florine Paraz, Mahesh M. Bandi Turbulent flows represent a strongly correlated classical field characterised by strong velocity fluctuations in space and in time, which are not independent of one another. Focusing only on temporal velocity measurements, a discrete Eulerian point and a continuous Eulerian field measurement represent the two limits, and each yields its own spectrum. We ask, how does the temporal, Eulerian point spectrum converge towards the temporal Eulerian field spectrum as one increases the number of discrete sampling points across the field. We discuss preliminary experiments in both two and three dimensional turbulence. We exploit the breakdown of Galilean invariance for higher order velocity spectra to understand convergence from discrete point to continuous field limits {\it via} spatial sparse sampling. [Preview Abstract] |
Thursday, March 16, 2017 1:15PM - 1:27PM |
S12.00011: Bridging the Gap Between Stationary Homogeneous Isotropic Turbulence and Quantum Mechanics Siavash Sohrab A statistical theory of stationary isotropic turbulence $^{1}$ is presented with eddies possessing Gaussian velocity distribution, Maxwell-Boltzmann speed distribution in harmony with perceptions of Heisenberg $^{2}$, and Planck energy distribution in harmony with perceptions of Chandrasekhar$^{3}$ and in agreement with experimental observations of Van Atta and Chen (\textit{J. Fluid Mech. }34 (3) \quad 497-515, 1968). Defining the action $S=-m\Phi $ in terms of velocity potential of atomic motion, scale-invariant Schr\"{o}dinger equation is derived$^{1\, }$from invariant Bernoulli equation. Thus, the gap between the problems of turbulence and quantum mechanics is closed through connections between Cauchy-Euler-Bernoulli equations of hydrodynamics, Hamilton-Jacobi equation of classical mechanics, and finally Schr\"{o}dinger equation of quantum mechanics. Transitions of particle (molecular cluster c$_{ji})$ from a small rapidly-oscillating eddy e$_{j}$ (high-energy level-j) to a large slowly-oscillating eddy e$_{i}$ (low energy-level-i) leads to emission of a sub-particle (molecule m$_{ji})$ that carries away the excess energy $\varepsilon_{ji} =h(\nu_{j} -\nu_{i} )$ in harmony with Bohr theory of atomic spectra. $\backslash \backslash $ $^{1}$ Sohrab, S. H.,\textit{ Chaotic Modeling and Simulation} (CMSIM) \textbf{3}, 231-245\textbf{ }(2016). $^{2}$ Heisenberg, W., \textit{Proc. Roy. Soc. }A \quad \textbf{159}, 402-406 (1948). $^{3}$ Chandrasekhar, S., \textit{Stochastic, Statistical, and Hydrodynamic Problems in Physics and Astronomy}, Selected Papers, vol.3, University of Chicago Press, Chicago, 515-528, 1989. [Preview Abstract] |
Thursday, March 16, 2017 1:27PM - 1:39PM |
S12.00012: Spontaneous mirror-symmetry breaking induces inverse energy cascade in 3D active fluids Jonasz Slomka, Jorn Dunkel Classical turbulence theory assumes that energy transport in a 3D turbulent flow proceeds through a Richardson cascade whereby larger vortices successively decay into smaller ones. By contrast, an additional inverse cascade characterized by vortex-mergers exists in 2D fluids and gases, with profound implications for meteorological flows and fluid mixing. The possibility of a helicity-driven inverse cascade in 3D fluids had been rejected in the 1970s based on equilibrium-thermodynamic arguments. Recently, however, it was proposed that certain symmetry breaking processes could potentially trigger a 3D inverse cascade, but no physical system exhibiting this phenomenon has been identified to date. Here, we present direct analytical and numerical evidence for the existence of a robust inverse energy cascade in 3D active fluids, such as bacterial suspensions, which can develop flows that spontaneously break mirror-symmetry. We show analytically that self-organized scale selection, a generic feature of many biological and engineered nonequilibrium fluids, can generate parity-violating Beltrami flows. Using large-scale numerical simulations, we further demonstrate how active scale selection controls mirror-symmetry breaking and the emergence of a 3D inverse cascade. [Preview Abstract] |
Thursday, March 16, 2017 1:39PM - 1:51PM |
S12.00013: Higher harmonic forces in the flow-induced response of bluff bodies with broken symmetry. Yahya Modarres-Sadeghi, Banafsheh Seyed-Aghazadeh, Daniel Carlson A flexibly-mounted uniform cylinder placed in a uniform flow is a canonical configuration for understanding vortex-induced vibration, where the structure is perfectly symmetric with respect to the incoming flow. Several other configurations exist in which the geometrical symmetry of the system is broken, such as an inclined cylinder in which the cylinder is placed with an angle with respect to the incoming flow direction, or a tapered cylinder in which the diameter of the circular cylinder varies along its length, or when the geometry of the cross-section changes from circular to other shapes such as square or triangle. Also, in some other cases, such as a bluff body forced to rotate about its long axis, the symmetry of the surrounding wake is broken by the rotation imposed on the cylinder. Here we focus on flow-induced responses of such systems based on a series of experiments conducted in a recirculating water tunnel. In particular, we discuss how flow forces at frequencies of twice and three times the shedding frequency do exist in the measured cross-flow forces. [Preview Abstract] |
Thursday, March 16, 2017 1:51PM - 2:03PM |
S12.00014: Experiments in Environmental$~$Flows: Flow over Large-Scale Topography Ali M. Hamed, Leonardo P. Chamorro In order to provide a better understanding of the flow over large-scale topography relevant to environmental applications, particle image velocimetry (PIV) was used in a refractive-index-matching (RIM) channel to study the flow over 2D and 3D walls defined by the same length scale and occupying roughly 10{\%} of the boundary layer. A series of experiments were performed to investigate the impact of roughness three-dimensionality on the flow field in developed turbulent flow, developing turbulent flow, and the transition to turbulence regime. The results show that 3D topographies (in contrast to 2D ones) have characteristic spanwise flows within the topography that relatively reduce spanwise vorticity leading to reduced drag and turbulent activity. Furthermore, turbulent boundary layers exhibit a distinctive response to an abrupt large-scale topographic change depending on whether the topography is 2D or 3D. For example, the integral parameters (e.g., displacement and momentum thicknesses) are significantly more modulated by the topography in the 2D case due to large pressure variations in the streamwise direction. The three-dimensionality of the topography also impacts the nature by which the boundary layer transitions to turbulence. The transition over the 2D topography occurs due to an inflection point in the velocity profile resulting from flow separation within the roughness troughs. In the 3D case, the transition is significantly delayed due to the lack of such instability. [Preview Abstract] |
Thursday, March 16, 2017 2:03PM - 2:15PM |
S12.00015: Water wave propagation over a controlled bathymetry Philippe Petitjeans, Agnès Maurel, Vincent Pagneux, Tomash Bobinski An experimental study concerning the usage of metamaterials for water waves control is presented. Two applications are considered: Firstly, we show how to focus water waves using analogy to a group of metamaterials called epsilon-near-zero. The second considered application of metamaterials for water waves is hiding (cloaking) defects in a waveguide from the far field observer. The efficiency of bathymetry is evaluated in term of scattering properties. The influence of water wave dispersivity on the cancellation of scattering is also determined. Cloaking properties of the obtained bathymetry is experimentally confirmed using a wave packet characterized by broadband spectrum. In the second part, we show how to cloak a cylinder that is shifted from the centerline of a waveguide. Smooth cloaking bathymetry surrounding a cylinder is able to significantly reduce the scattering in broad range of frequencies. The experimental counterparts confirmed increase in transmission with respect to a reference case with flat bathymetry. [Preview Abstract] |
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