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 L02: Multiphase Flows: Modeling and Theory II |
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Chair: Duan Zhang, Los Alamos National Laboratory Room: 2B |
Monday, November 25, 2019 1:45PM - 1:58PM |
L02.00001: High-Fidelity Simulation of a Rotary Bell Atomizer with Electrohydrodynamic Effects Venkata Krisshna, Mark Owkes Rotary Bell Atomizers (RBA) are extensively used as paint applicators in the automotive industry. Atomization of paint is achieved by a bell cup rotating at high speeds (40k-60k RPM) and in the presence of a background electric field. Current estimates report a maximum paint transfer efficiency of only 60\%. The atomization process in an RBA affects the droplet size and velocity distribution which subsequently control the transfer efficiency and surface finish quality. Moreover, optimal spray parameters used in industry are often obtained from expensive trial-and-error methods. In this work, a computational approach is used to simulate three-dimensional near-cup flows (mainly primary and secondary breakup) using a high-fidelity volume-of-fluid transport scheme that includes the effects of Electrohydrodynamics (EHD). This work involves the use of two meshes, one to solve the Navier-Stokes equations in the atomization region and a second on a larger region to solve for the electric field with realistic boundary conditions. This research aims to develop a cost-effective method to investigate the influence of various flow characteristics on the atomization and breakup process of the liquid. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L02.00002: An Eulerian-Eulerian CFD Study of Surface Wetting at Different Richardson Numbers in Dispersed Oil-Water Pipe Flow Jakob Roar Bentzon, Jens Honore Walther An Eulerian-Eulerian two-phase CFD model has been employed to investigate the variation of dispersion and liquid holdup in the horizontal section of wells used for oil production under operating conditions with water-cuts ranging from $25$--$75\,\%$. The employed model uses a S-gamma droplet distribution model to estimate droplet sizes based on statistical moments with breakup and coalescence models. The model has been validated against experimental measurements with good accuracy on phase distribution but challenges obtaining correct droplet sizes. Consequently, the model is used to study different flow conditions, namely at varied Richardson numbers through changing the Froude number and the Atwood number separately. From the results, it is observed that similarly to what is seen in the Kelvin-Helmholtz instability, a higher Richardson number reduces mixing of the interface and thus decreases the rate of dispersion. Slight differences in the results from varying the Atwood number and the Froude number to same Richardson numbers are observed on both dispersion and liquid holdup [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L02.00003: Thermal and Fluid Dynamics of Snow vs. Rain at the Air-Water Interface Mehdi Vahab, Kourosh Shoele, David Murphy The effects of precipitation in the forms of rain, snow, and hail are studied using computational methods for multimaterial/multiphase systems. The comparison of single droplet impacts shows the phase-dependency (a liquid or solid droplet) of the momentum and energy transfer to the surface and body of water. The depth of penetration and the resultant vertical flow are found highly dependent on the phase-change rate of the droplet. Multiple models of snow particles with systematic geometrical complexities are tested for the role of shape in air pocket entrapment at the impact. The sensitivity of the single droplet impact dynamics is also studied by varying droplets size and temperature, and are used for investigation of the precipitation events with the average ensemble effects of multiple droplet impacts. The size and velocity of the droplets are set based on the observed size/velocity distribution of frequent rain, hail, or snow events. A predictive model is developed to predict the changes in the water surface and body energy content following each precipitation event. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L02.00004: Assessment of surfactant models with applications to crude oil-water coalescence or aggregation modeling Shaolin Mao We study surfactant models with focus on crude oil -- sea water aggregation/coalescence analysis and modeling. Undesired crude oil-water emulsion exists in most crude oil production and recovery process; therefore, costly process such as destabilizing of oil-water emulsion in petroleum engineering is required from reservoirs, wellbores, to wellheads and transport of crude oil. This research is limited to physics of coalescence or aggregation of water in oil mixing (crude oil is the dominant phase). Parameter studies will be conducted in this work to assess surfactant models, elucidate the factors which influence the aggregation/coalescence of crude oil-sea water mixing process. Numerical simulation is based on commercial CFD tool such as ANSYS FLUENT by using population balance model (PBM) coupling with CFD solvers. Experimental observation and comparison will also be given.. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L02.00005: Manipulating gas-assisted atomization by inlet gas turbulence Delin Jiang, Yue Ling, Daniel Fuster, Stephane Zaleski, Gretar Tryggvason In an airblast atomization process, the destabilization and breakup of a liquid jet is assisted by a co-flowing high speed gas stream. Recent experiments and simulations show that the inlet gas turbulence has a strong impact on the interfacial instability development near the nozzle exit and also the liquid breakup downstream. In this study we will systematically investigate the effect of inlet gas turbulence on the interfacial instability and spray formation through high-fidelity simulation. The gas-liquid interface is resolved by a momentum-conserving volume-of-fluid method. A digital filter approach is used to generate temporally and spatially correlated velocity fluctuations at the gas inlet. The dominant frequency and spatial growth rate of the mixing layer are observed to increase significantly with the inlet gas turbulence intensity. The dominant frequency predicted by simulations are in a good agreement with the experimental data. Spatial-temporal viscous linear instability analysis is also conducted using the eddy-viscosity model. The simulation results also reveal the change of dominant breakup mechanism when gas inlet turbulence is present. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L02.00006: Sloshing and its effects on thermal mixing in aircraft fuel tanks Connor Rohmann-Shaw, Duncan Borman, Mark Wilson Modern aircraft designs are becoming ever more complex, with higher demands on their performance capabilities. As the thermal loads from the airframe, engine, electrical systems etc. increase, one of the key challenges is thermal management. A solution is to use the fuel as a coolant; fuel is used as a heat sink for components around the aircraft and then recirculated back into the fuel tanks. To fully optimise this method however we must expand upon existing thermal management models by better understanding the thermal mixing process internal to the fuel tanks, with particular attention given to the role of fuel sloshing. The multi-phase Volume of Fluid method of free-surface tracking is used to predict fluid motion, which we couple to the thermal flow field using the Boussinesq approximation. Using these numerical simulations, we investigate the effect that sloshing has on thermal mixing, allowing us to inform future design considerations. Experiments undertaken using thermocouples to measure the evolution of the temperature field in a turbulent free-surface flow will also be presented. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L02.00007: Effect of inertial forces on constitutive behaviors of the RVE granular model Min Wang, Duan Zhang A representative volume element (RVE) granular model has been used in multiscale simulations. For problems of large material deformations particles in RVE are often re-initialized leading to the loss of history information important for many granular materials, especially under a dynamical loading. A new algorithm for using the periodic boundary condition is developed to accommodate the large deformation of the material while maintaining the RVE as a rectangular box. Reinitialization of the RVE is never needed even for extremely large deformations. The algorithm is based on the decomposition of the velocity gradient into an upper-triangular tensor and a spin tensor. The deformation resulting from the upper-triangular tensor is treated by a modified algorithm using the periodic boundary condition. The effect of the spin tensor is accounted for by using a rotating frame of reference. The effects of inertial forces, such as the centrifuge and the Coriolis forces, are considered. In particular, we study the effect of rotation to the stresses and the related objectivity issues when using such obtained stress in multiscale calculations. [Preview Abstract] |
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