Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session M17: Flow Instability: Multiphase Flow |
Hide Abstracts |
Chair: Omar Matar, Imperial College London Room: 205 |
Tuesday, November 24, 2015 8:00AM - 8:13AM |
M17.00001: Three-dimensional numerical simulations of three-phase slug flows in horizontal pipes Yan Wang, Junfeng Yang, Omar Matar One of the most common flow regimes in pipelines is that of slug flow: slug bodies corresponding to alternating blocks of aerated liquid which bridge the pipe, separated by elongated bubbles; the latter ride atop a liquid layer. The slugs travel at velocities that exceed the mixture superficial velocity; this can potentially cause structural damage, particularly at pipe bends and junctions. Two-phase slug flows have received considerable attention in the literature both experimentally and computationally but there has been very little work carried out on three-phase slugging. In the present work, the evolution of oil-water-air three-phase slug flow in a horizontal cylindrical pipe is investigated using two-dimensional and three-dimensional computational fluid dynamics simulations. The parameters characterising three-phase slug flow, e.g. slug length, propagation velocity, and slug formation frequency, are determined for various gas and liquid superficial velocities for a given pipe geometry. The results of this work are compared to available experimental data and numerical solutions based on approximate, one-dimensional models relying on the use of empirical correlations. [Preview Abstract] |
Tuesday, November 24, 2015 8:13AM - 8:26AM |
M17.00002: The stability of Taylor bubbles in large-diameter tubes: Linear theory Habib Abubakar, Omar Matar Taylor bubbles are a characteristic feature of the slug flow regime in gas-liquid pipe flows. With increasing pipe diameter, previous experimental observations have shown that at sufficiently large diameter ($>$ 0.1 m), the slug flow regime, and hence Taylor bubbles, are not observed in gas-liquid flows in vertical pipes. Numerical simulations of a Taylor bubble rising in a quiescent liquid (see companion talk at this APS/DFD conference) have also shown that the wake of Taylor bubbles rising in a riser of such sizes is turbulent and has great impact on the stability of the subsequent, trailing bubbles. In view of these observations, a linear stability analysis is carried out to establish the stability conditions for a Taylor bubble rising in a turbulent flowing liquid. The stability of an axisymmetric Taylor bubble to a small-amplitude, three dimensional, perturbation is studied and the dimensionless flow parameters of the liquid investigated include the Froude number, the inverse viscosity number, and the Eotvos numbers. [Preview Abstract] |
Tuesday, November 24, 2015 8:26AM - 8:39AM |
M17.00003: The stability of Taylor bubbles in large-diameter tubes: direct numerical simulations Amanjalot Dhanjal, Maya Saravan-Butler, Sydney Smith, Junfeng Yang, Omar Matar Slug flow corresponds to intermittent Taylor bubbles and liquid slugs, and is widely observed in the oil-and-gas industry. The fluctuating flow rate caused by Taylor bubbles is problematical; thus, the destabilisation of this regime would be beneficial. To gain better understanding of this regime in vertical tubes, three-dimensional CFD simulations of Taylor air bubble rise in initially stagnant water and progressively larger diameter tubes, are carried out. Tubes with diameters in the range of 0.032m-0.290m and a height of 2m are considered. The topology of the Taylor bubbles and their rise velocity are predicted and validated against experimental results. Our results suggest that the wake of leading bubbles plays a key role in the deformation and break-up of trailing bubbles. Motivated by these results, the effect of bubble separation distance, and aspect ratio, on bubble stability and the slug flow regime is investigated. [Preview Abstract] |
Tuesday, November 24, 2015 8:39AM - 8:52AM |
M17.00004: Parallel direct numerical simulation of three-dimensional spray formation Jalel Chergui, Damir Juric, Seungwon Shin, Lyes Kahouadji, Omar Matar We present numerical results for the breakup mechanism of a liquid jet surrounded by a fast coaxial flow of air with density ratio (water/air) $\sim $ 1000 and kinematic viscosity ratio $\sim$ 60. We use code BLUE, a three-dimensional, two-phase, high performance, parallel numerical code based on a hybrid Front-Tracking/Level Set algorithm for Lagrangian tracking of arbitrarily deformable phase interfaces and a precise treatment of surface tension forces. The parallelization of the code is based on the technique of domain decomposition where the velocity field is solved by a parallel GMRes method for the viscous terms and the pressure by a parallel multigrid/GMRes method. Communication is handled by MPI message passing procedures. The interface method is also parallelized and defines the interface both by a discontinuous density field as well as by a triangular Lagrangian mesh and allows the interface to undergo large deformations including the rupture and/or coalescence of interfaces. [Preview Abstract] |
Tuesday, November 24, 2015 8:52AM - 9:05AM |
M17.00005: Stability of a liquid jet in a weak crossflow Ghobad Amini, Mehdi Jadidi, Ali Dolatabadi The atomization of liquid jets in crossflow is a critical process in numerous engineering systems including fuel injection and thermal spray. In an effort to elucidate the primary breakup step, a theoretical model for three-dimensional linear stability of a viscous liquid jet injected in a weak gaseous cross flow is developed. Focusing on the early stages of the jet evolution, the problem is formulated for an oblique incidence of gas flow to the liquid jet. In the context of Kelvin-Helmholtz and Rayleigh-Taylor instabilities, a characteristic equation accounting for the growth of columnar and azimuthal waves is obtained and the most dominant wavelength and the corresponding growth rates are calculated. Symmetric and asymmetric modes of liquid jet disturbance are investigated for a wide range of viscous, surface tension, and aerodynamic force ratios. The predicted results for asymptotic cases of coflow and crossflow are examined against the experimental observations available in the literature. [Preview Abstract] |
Tuesday, November 24, 2015 9:05AM - 9:18AM |
M17.00006: Drop size selection in axially heated co-axial fiber capillary instability Saviz Mowlavi, Pierre-Thomas Brun, Francois Gallaire We analyze the sphere size selection mechanism in silicon-in-silica sphere formation through the application of an external axial thermal gradient to a co-axial silicon-in-silica fiber (Gumennik et al., Nature Com., 2013). We first apply a convective/absolute stability analysis to the in-fibre capillary instability governing the sphere formation and demonstrate that the resulting wavelength selection predicts a finite but still too large wavelength. A global stability analysis is then pursued, which accounts for the spatial inhomogeneity of the base flow. [Preview Abstract] |
Tuesday, November 24, 2015 9:18AM - 9:31AM |
M17.00007: Flapping jets and monodisperse droplets formed by the Kelvin-Helmholtz instability Oliver McRae, Antoine Gaillard, James Bird When a straw is used to blow air into a glass of liquid, typically one of two behaviors is observed: a dimple in the liquid's surface, or a frenzy of waves and bubbles. However, under certain conditions intermediate regimes can develop. In these regimes periodic waves progress into a flapping jet that can develop into monodisperse airborne droplets. The precise mechanism for the formation of these regimes is not well understood. Here we show that the Kelvin-Helmholtz instability is responsible for the formation of the flapping jet. We inject a continuous stream of gas into the liquid surface and observe both optically and acoustically the deformation of the liquid-air interface as we systematically adjust various parameters. Previous research has shown that the frequency of a liquid-gas oscillator can be regulated by the compressibility of the gas phase. Here we present the Kelvin-Helmholtz instability, with the treatment of the fluids as incompressible, as the regulator of the frequency. The formation of the jet droplets can thus be characterized by the Kelvin-Helmholtz and Rayleigh-Plateau instabilities. We anticipate the flapping jet phenomenon could be exploited to create monodisperse aerosols and emulsions, and may be relevant in analogous systems such as pulmonary flow. [Preview Abstract] |
Tuesday, November 24, 2015 9:31AM - 9:44AM |
M17.00008: Solutal Marangoni instability in layered two-phase flow Jason Picardo, T.G. Radhakrishna, S Pushpavanam In this work, the instability of layered two-phase flow caused by the presence of a surface-active solute is studied. The fluids are density matched to focus on surfactant effects. The fluids flow between two flat plates, which are maintained at different solute concentrations. This establishes a constant flux of soluble surfactant from one fluid to the other, in the base state. A linear stability analysis is carried out, supported by energy budget calculations. The flow is first analyzed in the creeping flow regime. Long wave as well as short wave Marangoni instabilities are identified, each with a distinct energy signature. The short wave instability manifests as two distinct modes, characterized by the importance of interfacial deformations or lack thereof. The primary instability switches between these different modes as parameters are varied. The effect of small but finite inertia on these solutal Marangoni modes is then examined. The effect of soluble surfactant on a finte inertia flow is also studied, with focus on the transition from the viscosity-induced instability to solutal Marangoni instability. This analysis is relevant to microfluidic applications, such as solvent extraction, in which mass transfer is carried out between stratified immiscible fluids. [Preview Abstract] |
Tuesday, November 24, 2015 9:44AM - 9:57AM |
M17.00009: The effect of surfactant on counter-current gas-liquid flows in vertical tubes Ivan Zadrazil, Omar Matar, Christos Markides Counter-current gas-liquid flows in vertical tubes are often accompanied by flow reversal. This so-called “flooding” phenomenon could occur for at least a part of the liquid phase from a counter-current to a co-current state, against the action of gravity. This phenomenon is of central importance to the oil-and-gas and nuclear industries, and has received considerable attention experimentally. The large majority of the previous work in this area, however, has considered the case of pure fluids, in the absence of additives; the latter are used frequently in industry in an attempt to control the onset of various flow regimes with little understanding of the mechanisms underlying their influence on the interfacial dynamics. In this study, we address this issue by investigating the dynamics of flooding in the presence of surfactants in a 4 m long, 32.4 mm nominal bore polymethyl methacrylate test section using high-speed shadowgraphy, and axial-view imaging. The system parameters include the superficial gas and liquid velocities, and surfactant concentration. We show that the presence of surfactant can have a dramatic effect on the flow structures and the onset of flooding. The mechanisms responsible for these phenomena are analysed. [Preview Abstract] |
Tuesday, November 24, 2015 9:57AM - 10:10AM |
M17.00010: Stability analysis of two phase stratified flow in a rectangular channel Dinesh Bhagavatula, Pushpavanam S Two phase stratified flows arise in extraction operations in microfluidic systems. It is well established that stratified flows in between two infinite plates is always unstable. However such flows are experimentally observed in micro channels. To understand this paradox we perform a linear stability analysis of stratified two phase Poiseuille flow in a rectangular duct. A two-dimensional fully developed flow through the rectangular channel is considered. The linearized equations along with the boundary conditions in primitive variable formulation are numerically solved using Chebyshev collocation method. All the primitive variables, which are the velocity and pressure fields, are retained in the linearised governing equations. Since boundary conditions for disturbance pressure do not exist, the corresponding compatibility conditions derived from the Navier-Stokes equations are collocated both at the walls and the interface. The resulting eigen-value problem is solved using a shift and invert Arnoldi algorithm. The role of different parameters such as Aspect ratio, density ratio, viscosity ratio on the stability characteristics is analyzed. The stability results are validated in the limit of large Aspect Ratios. The flow fields are sought as a combination of Chebyshev polynomials in both y and z directions. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700