Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session A33: Convection and Buoyancy Driven Flows: Numerical Simulations & Material ProcessingConvection
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Chair: Di Yang, University of Houston Room: 106 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A33.00001: Large-eddy simulation study of oil/gas plumes in stratified fluid with cross current. Di Yang, Shuolin Xiao, Bicheng Chen, Marcelo Chamecki, Charles Meneveau Dynamics of the oil/gas plume from a subsea blowout are strongly affected by the seawater stratification and cross current. The buoyant plume entrains ambient seawater and lifts it up to higher elevations. During the rising process, the continuously increasing density difference between the entrained and ambient seawater caused by the stable stratification eventually results in a detrainment of the entrained seawater and small oil droplets at a height of maximum rise (peel height), forming a downward plume outside the rising inner plume. The presence of a cross current breaks the plume's axisymmetry and causes the outer plume to fall along the downstream side of the inner plume. The detrained seawater and oil eventually fall to a neutral buoyancy level (trap height), and disperse horizontally to form an intrusion layer. In this study, the complex plume dynamics is investigated using large-eddy simulation (LES). Various laboratory and field scale cases are simulated to explore the effect of cross current and stratification on the plume dynamics. Based on the LES data, various turbulence statistics of the plume are systematically quantified, leading to some useful insights for modeling the mean plume dynamics using integral plume models. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A33.00002: DNS of unsteady, turbulent convection in a rotating stratified fluid. Anikesh Pal, Vamsi Chalmalla Turbulent convection under the influence of intense surface cooling and earth's rotation is a common phenomenon observed in the ocean. In the present study, direct numerical simulations are performed to understand this dynamics. The effect of rotation is represented by Rossby number $Ro^*$ which is defined in terms of ocean depth $H$, Coriolis parameter $f$ and surface buoyancy flux $B_0$, as $Ro^* = \frac{B_0^{1/2}}{H f^{3/2}}$. Cooling at the surface results in the formation of unstable density configuration where denser fluid lies on top of the lighter fluid. These unstable density configuration leads to a turbulent front. When the turbulent front reaches a transition depth $z_c$, it experiences the effect of rotation leading to the formation of quasi- 2D vortices beneath the 3D turbulent layer. If the surface cooling is strong enough, these vortices penetrate further downwards producing vortex columns. Qualitatively, DNS results agree well with the findings of experimental study by Maxworthy $\&$ Narimousa(1993). The motivation of this study is to understand the nonlinear dynamics and turbulence scaling as the surface cooling and Coriolis parameter are varied. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A33.00003: Solutal convection induced by dissolution. Influence on erosion dynamics and interface shaping. Michael Berhanu, Julien Philippi, Cyril Ozouf, Caroline Cohen, Julien Derr, Sylvain Courrech du Pont Dissoluble minerals are often shaped by chemical erosion. In the case of fast kinetics of dissolution, local erosion rate is set by the advection of the solute. Even in absence of an imposed or external flow, advection can drive the dissolution, when buoyancy effects due to gravity induce a solutal convective flow, which controls the erosive dynamics and modifies the shape of the dissolving interface. Here, we investigate for fast dissolving materials like salt, solutal convection induced by dissolution. Results are interpreted regarding a linear stability analysis of the corresponding solutal Rayleigh-Benard instability, to predict onset time of convection, when a dissolving surface is suspended above water initially at rest. Then solutal convection induces pattern on the dissolving interface, whose dynamics is also investigated. More generally, we inquire what are the conditions to observe a such solutal convection instability in geological situations and if the properties of dissolution patterns can be related to the characteristic of the convective flow. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A33.00004: Numerical study of two-dimensional solutal convection Julien Philippi, Michael Berhanu, Julien Derr, Sylvain Courrech du Pont Solutal convection can occur when a dissolving surface is suspended above a water height, initially at rest. Convection increases the erosion velocity and creates dissolution patterns as reported in C. Cohen et al., Phys. Rev. Fluids, 1, 050508 (2016). To resolve the solute concentration boundary layer, which is not possible experimentally, 2D numerical simulations of solutal convection are performed using the open-source code FreeFem ++ (finite elements, adaptive mesh refinement). In a first step, solute flux is transported through a growing diffusion layer. Then after an onset time, once the layer exceeds critical width, convection flow starts under the form of falling plumes. A dynamic equilibrium results in average from births and deaths of intermittent plumes, setting the size of the solute concentration boundary layer at the interface and thus the erosion velocity. Therefore it becomes possible to study quantitatively the relation between the receding velocity of dissolving solids and the concentration field. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A33.00005: ABSTRACT WITHDRAWN |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A33.00006: Computational Modeling of Ablation on an Irradiated Target Igbal Mehmedagic, Siva Thangam Computational modeling of pulsed nanosecond laser interaction with an irradiated metallic target is presented. The model formulation involves ablation of the metallic target irradiated by pulsed high intensity laser at normal atmospheric conditions. Computational findings based on effective representation and prediction of the heat transfer, melting and vaporization of the targeting material as well as plume formation and expansion are presented along with its relevance for the development of protective shields. In this context, the available results for a representative irradiation from 1064 nm laser pulse is used to analyze various ablation mechanisms, variable thermo-physical and optical properties, plume expansion and surface geometry. [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A33.00007: Development of buoyant currents in yield stress fluids P. Rossi, I. Karimfazli Infinitesimal perturbations are known to decay in a motionless yield stress fluid. We present experimental evidence to reveal other mechanisms promoting free advection from a motionless background state. Development of natural convection in a cavity with differentially heated side-walls is investigated as a benchmark. Velocity and temperature fields are measured using particle image velocimetry/thermometry. We examine time evolution of the flow, compare experimental findings with theoretical predictions and comment on the striking features brought about by the yield stress. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A33.00008: Stability of a density-change flow in the solidification of a ternary alloy Peter Guba, Daniel Anderson We consider phase-change driven flow and solidification of a ternary (three-component) alloy. The ternary system is characterized by the formation of two distinct mushy layers (primary and secondary), distinguished by the number of components present in their solid phases. A primary layer has the solid phase composed of a single component and, beneath the primary layer, a secondary layer has the solid phase composed of two components. Generally, the densities of the liquid, primary solid and secondary solid phases during solidification are different, and these differences give rise to a flow of the interstitial liquid. We identify four different flow regimes dependent upon whether the two solid phases shrink or expand upon solidification. The stability of this density-change flow in the absence of buoyancy is studied numerically applying a spectral method. A simple power law is employed to describe the permeability of the ternary mushy layers, with a sensitivity of permeability to changes in porosity used as the control parameter. An instability is found to occur not only in the case of expansion but also contraction, an option that is apparently unavailable for the binary case. A reduced model is derived which contains the bare essentials required to capture this instability. [Preview Abstract] |
Sunday, November 19, 2017 9:44AM - 9:57AM |
A33.00009: Wash-away of contaminant downstream of a backward-facing step over a range of Schmidt number. Hannah Min, Paul F. Fischer, Arne J. Pearlstein We report computations of two-dimensional unsteady convective mass transfer in flow over a backward-facing step, in which a contaminant initially present downstream of the step is "washed away". Results are presented for a range of Schmidt numbers, showing how the recirculation region downstream of the step not only serves to retain contaminant near the step, but also transports contaminant \textit{upstream} towards the step. The results for the highest Schmidt number considered (2650) are relevant to wash-away of low-molecular weight species in liquids, for which some implications are discussed. [Preview Abstract] |
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