Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session E34: Turbulence: Multiphase Flow |
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Chair: Don Bergstrom, University of Saskatchewan Room: Oregon Ballroom 203 |
Sunday, November 20, 2016 5:37PM - 5:50PM |
E34.00001: Numerical simulation of turbulent slurry flows Mohammad Reza Haghgoo, Reymond J. Spiteri, Donlad J. Bergstrom Slurry flows, i.e., the flow of an agglomeration of liquid and particles, are widely employed in many industrial applications, such as hydro-transport systems, pharmaceutical batch crystallizers, and wastewater disposal. Although there are numerous studies available in the literature on turbulent gas-particle flows, the hydrodynamics of turbulent liquid-particle flows has received much less attention. In particular, the fluid-phase turbulence modulation due to the particle fluctuating motion is not yet well understood and remains challenging to model. This study reports the results of a numerical simulation of a vertically oriented slurry pipe flow using a two-fluid model based on the kinetic theory of granular flows. The particle stress model also includes the effects of frictional contact. Different turbulence modulation models are considered, and their capability to capture the characteristic features of the turbulent flow is assessed. The model predictions are validated against published experimental data and demonstrate the significant effect of the particles on the fluid-phase turbulence. [Preview Abstract] |
Sunday, November 20, 2016 5:50PM - 6:03PM |
E34.00002: Micro-bubbles and Micro-particles are Not Faithful Tracers of Turbulent Acceleration Chao Sun, Varghese Mathai, Enrico Calzavarini, Jon Brons, Detlef Lohse We report on the Lagrangian statistics of acceleration of small (sub-Kolmogorov) bubbles and tracer particles with Stokes number St $\ll$1 in turbulent flow. At decreasing Reynolds number, the bubble accelerations show deviations from that of tracer particles, i.e. they deviate from the Heisenberg-Yaglom prediction and show a quicker decorrelation despite their small size and minute St. Using direct numerical simulations, we show that these effects arise due the drift of these particles through the turbulent flow. We theoretically predict this gravity-driven effect for developed isotropic turbulence, with the ratio of Stokes to Froude number or equivalently the particle drift-velocity governing the enhancement of acceleration variance and the reductions in correlation time and intermittency. Our predictions are in good agreement with experimental and numerical results. The present findings are relevant to a range of scenarios encompassing tiny bubbles and droplets that drift through the turbulent oceans and the atmosphere. [Preview Abstract] |
Sunday, November 20, 2016 6:03PM - 6:16PM |
E34.00003: Coalescence and Break-up of large, deformable droplets with different viscoties in turbulent channel flow Alessio Roccon, Francesco Zonta, Alfredo Soldati The dynamics of large, deformable droplets released in a turbulent channel flow is numerically analyzed. Pseudo-Spectral direct numerical simulations are based on the resolution of the coupled Navier-Stokes and Cahn-Hiliard equations (Phase-Field Model). The droplets have the same density but different viscosity compared to the surrounding fluid. We first focus on droplets coalescence and break-up rate. Two different dynamic are observed, depending on the Weber number $We$, (which measures the ratio between the inertial forces and the surface tension forces) and the viscosity ratio $\lambda$, (ratio between the viscosity of the drop and the continuous phase). For small We, droplets are only slightly deformed and their viscosity does not influence much the coalescence/break-up rate. For larger We, droplets are deformable and their viscosity can significantly alter the coalescence and break-up dynamics. [Preview Abstract] |
Sunday, November 20, 2016 6:16PM - 6:29PM |
E34.00004: Viscosity stratified fluids in turbulent channel flow Alfredo Soldati, Somayeh Ahmadi, Alessio Roccon, Francesco Zonta Direct Numerical Simulation (DNS) is used to study the turbulent Poiseuille flow of two immiscible liquid layers inside a rectangular channel. A thin liquid layer (fluid 1) flows on top of a thick liquid layer (fluid 2), such that their thickness ratio is $h_1/h_2 = 1/9$. The two liquid layers have the same density but different viscosities (viscosity-stratified fluids). In particular, we consider three different values of the viscosity ratio $\lambda=\nu_1/\nu_2$: $\lambda=1$, $\lambda=0.875$ and $\lambda=0.75$. Numerical Simulations are based on a Phase Field method to describe the interaction between the two liquid layers. Compared with the case of a single phase flow, the presence of a liquid-liquid interface produces a remarkable turbulence modulation inside the channel, since a significant proportion of the kinetic energy is subtracted from the mean flow and converted into work to deform the interface. This induces a strong turbulence reduction in the proximity of the interface and causes a substantial increase of the volume-flowrate. These effects become more pronounced with decreasing $\lambda$. [Preview Abstract] |
Sunday, November 20, 2016 6:29PM - 6:42PM |
E34.00005: In-situ Measurements of Cloud Droplet Dynamics Jan Molacek, Gholamhossein Bagheri, Haitao Xu, Eberhard Bodenschatz We present an in-situ experiment investigating the dynamics of cloud droplets and its dependence on the turbulent flow properties. This dynamics plays a major role in the rate of growth of cloud particles by coalescence and the resulting precipitation rate. The experiment takes place at a mountain research station at an altitude of 2650m, and makes use of a movable platform that can travel with the mean wind velocity over a distance of 5m and at speeds of up to 7.5m/s. Moving with mean velocity enables us to follow individual cloud particles over longer intervals, thus improving the quality of the statistics. Simultaneous measurements of other variables such as droplet size distribution and humidity fluctuations are done in order to develop a complete picture of the microphysical conditions within clouds. Preliminary results will be presented and discussed. [Preview Abstract] |
Sunday, November 20, 2016 6:42PM - 6:55PM |
E34.00006: Determining the Discharge Rate from a Submerged Oil Leaks using ROV Video and CFD study Pankaj Saha, Frank Shaffer, Mehrdad Shahnam, Omer Savas, Dave DeVites, Timothy Steffeck The current paper reports a technique to measure the discharge rate by analyzing the video from a Remotely Operated Vehicle (ROV). The technique uses instantaneous images from ROV video to measure the velocity of visible features (turbulent eddies) along the boundary of an oil leak jet and subsequently classical theory of turbulent jets is imposed to determine the discharge rate. The Flow Rate Technical Group (FRTG) Plume Team developed this technique that manually tracked the visible features and produced the first accurate government estimates of the oil discharge rate from the Deepwater Horizon (DWH). For practical application this approach needs automated control. Experiments were conducted at UC Berkeley and OHMSETT that recorded high speed, high resolution video of submerged dye-colored water or oil jets and subsequently, measured the velocity data employing LDA and PIV software. Numerical simulation have been carried out using experimental submerged turbulent oil jets flow conditions employing LES turbulence closure and VOF interface capturing technique in OpenFOAM solver. The CFD results captured jet spreading angle and jet structures in close agreement with the experimental observations. [Preview Abstract] |
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