Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session M22: Multiphase Flows: Atomization and Sprays I |
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Chair: Wayne Strasser, Liberty University Room: North 222 AB |
Monday, November 22, 2021 1:10PM - 1:23PM |
M22.00001: The effect of Electrostatic Forcing on the Droplet Distributions in Swirling Coaxial Atomization Rodrigo Osuna-Orozco, Xinzhi Xue, Nathanael Machicoane, Peter D Huck, Alberto Aliseda Multiphysics actuation is a promising strategy for versatile control of atomization. We present results of an experimental study where electrostatic forcing is applied at the nozzle of a swirling coaxial airblast atomizer, and along the mid-field spray development. Laser interferometry (PDPA) measurements of droplet sizes, as well as of axial and radial velocities, were collected across a representative cross section of the spray, over a wide range of gas to liquid momentum ratios, gas swirl ratios and electric field strengths. Electrostatic forcing resulted in smaller mean droplet diameters, especially for the lower momentum ratios studied. We observed significant increases in the axial and radial droplet velocities due to electrostatic acceleration, leading to more radially uniform sprays. These effects were detectable at all swirl ratios explored. Larger relative increases in the velocities of smaller droplets due to electrostatic effect contribute to the more uniform profiles of electrified sprays. Finally, we compare the observed droplet concentration and mean droplet diameter radial profiles with simple models that account for the electrostatic forcing of the spray, together with a simple scaling law for the electric charge density of each droplet. |
Monday, November 22, 2021 1:23PM - 1:36PM |
M22.00002: Novel Induced Drag Predictions using CFD; Applications to Sprayed Liquid Flaps George Loubimov, Michael P Kinzel, Douglas H Fontes A novel approach to estimating induced drag using Computational Fluid Dynamics (CFD) has recently been proposed. The proposed methodology involves calculating the induced drag of finite wings from viscous CFD simulations by means of momentum and energy balances. The application of this approach was previously limited to attached flows which were validated against analytic solutions. The present effort aims to apply this methodology to finite wings equipped with a Sprayed Liquid Flap (SLF). SLFs modify the conventional Jet Flap by replacing the gaseous jet with an atomized liquid spray. The addition of this second fluid phase introduces complex aerodynamic interactions with the freestream which are not readily assessable using a momentum-balance analysis. Hence, the application of this novel, energy-balance approach is well suited to gain insight into these complex phase interactions. This report aims at decomposing the drag provided by momentum conservation into viscous and inviscid criteria by means of a control volume, energy-balance analysis. Furthermore, an attempt is made to qualitatively describe the complex fluid interactions due to the injection of the liquid jet. |
Monday, November 22, 2021 1:36PM - 1:49PM |
M22.00003: Effect of Static Contact Angle in Simulations of Coaxial Gas-assisted Atomization Lam X Vu, Nathanael Machicoane, Olivier Desjardins Atomization plays a crucial role in many engineering systems such as combustion engines and agricultural sprays. Air-blast atomization is a specific spray strategy which relies on a high-speed gas to shear and break up a low-speed liquid, transferring its kinetic energy into liquid surface energy. In studies of air-blast atomization in a coaxial geometry, X-ray radiographs have shown non-trivial contact line dynamics and simulations have shown a strong dependence of the contact line boundary condition on the spray. In this study, we perform simulations of air-blast atomization at fixed atomization conditions but vary the static contact angle. Simulations are performed using a conservative finite volume flow solver with phase tracking handled using an un-split, geometric volume-of-fluid method. The static contact angle is modeled by adding a sub-grid scale interfacial tension force at the triple contact line. A single-phase nozzle simulation is run concurrently and coupled with the atomization simulation to yield realistic gas velocity inflow conditions. Our simulations are validated against experiments by comparing jet-width statistics and liquid mass distribution in the near-field. Finally, we discuss the effect of static contact angle on streamwise interfacial wave characteristics. |
Monday, November 22, 2021 1:49PM - 2:02PM |
M22.00004: An evaluation of drop size and injection angle in near-field spray calculations Michael Mason, Mario F Trujillo A common feature in Lagrangian-Eulerian spray models is the prediction of droplet size and the initial spreading angle of the spray at the nozzle exit. In the present work, the importance of drop size and spreading angle are evaluated by employing high-fidelity atomization simulations using an algebraic VoF approach (interFoam). The process begins by extracting an axial drop size profile (D32VoF) from VoF results and imposing this profile directly on LE calculations, thereby excluding all breakup models and isolating the effect of the LE calculations on the accuracy of the spray predictions. This LE accuracy is evaluated based on comparisons to projected mass density maps generated by the VoF calculations. The results show that, even with the imposition of the D32VoF profile, the LE calculations exhibit significant errors in comparison to VoF results. This discrepancy emphasizes that having the correct breakup model in LE computations can still lead to substantial difficulties. Additionally, the spreading angle is found to play a much more critical role in the prediction of spray mass distribution in comparison to drop size. A key ingredient missing in LE calculations, which is primarily responsible for the errors observed, is the ability of the LE spray model to replicate the axially developing spreading angle, which we believe is partially based on the complex momentum transfer between the gas phase and a large population of dynamically evolving and highly non-spherical liquid elements. |
Monday, November 22, 2021 2:02PM - 2:15PM |
M22.00005: Smart Biosludge Atomization for Waste-to-Energy Conversion Wayne Strasser, Daniel Wilson We introduce a novel "smart atomization" system to immediately accommodate and mitigate dynamically varying viscosity in a biosludge atomizer. Direct spray injection of a highly concentrated biosludge into a boiler could provide a new means of efficiently extracting energy from human or animal waste. Critical to this process, however, is an atomization system that maintains consistent droplet size production for combustion despite widely varying viscosities. High viscosity leads to a restrictive biosludge pressure drop and decreased atomization quality. CFD simulations are used to model biosludge atomization in a steam-assisted twin-fluid atomizer. To improve robustness, we transform the biosludge atomizer into a smart atomization system by adding two simultaneous, yet independent, PID controllers. The first PID controller adjusts the biosludge feed to maintain a constant pressure drop in the biosludge annulus. The second PID controller adjusts the steam feed to maintain constant droplet sizes, thereby compensating for the phase momentum ratio. We demonstrate the efficacy of the smart atomization system in maintaining consistent droplet sizes for a 100-fold increase in biosludge viscosity. To do so, however, the biosludge throughput is dramatically reduced, pointing to the need for a variable-geometry atomizer design. |
Monday, November 22, 2021 2:15PM - 2:28PM |
M22.00006: Subgrid-scale Modeling of Liquid Sheet Fragmentation Austin Han, Olivier Desjardins In this talk, we present a method for the prediction of the drop-size distribution from the aerodynamic breakup of a liquid sheet whose interface is maintained below the mesh size. A two-plane interface reconstruction is used within an Eulerian volume of fluid solver to capture the subgrid-scale sheet interface, while an algorithm based on connected component labeling is used to identify thin fluid regions that should undergo breakup. A sheet breakup model is then applied to the identified fluid regions to convert the associated Eulerian volume representation into droplets represented as Lagrangian point particles. The method is validated using canonical simulations of a perturbed sheet in a periodic domain and of a spherical drop. We investigate the ability of the method to predict the behavior of the spherical drop at different breakup regimes characterized by the non-dimensional Weber number with comparisons to experimental drop-size distributions. We also perform mesh-refinement studies to determine the meshsize-dependence of the method which then informs the computational cost of the implementation of the proposed method in full-scale atomization simulations. |
Monday, November 22, 2021 2:28PM - 2:41PM |
M22.00007: Impact of inlet gas turbulence on longitudinal and transverse instabilities in a two-phase mixing layer Delin Jiang, Yue Ling Understanding the development and breakup of interfacial waves in a two-phase mixing layer between the gas and liquid streams is paramount to atomization. Due to the velocity difference between the two streams, the shear on the interface triggers a longitudinal instability, which develops to interfacial waves that propagate downstream. Depending on the injection and geometric conditions, the longitudinal instability can be convective instability, absolute instability controlled by surface tension, and absolute instability controlled by geometric confinement. As the interfacial waves grow spatially, transverse modulations arise, turning the interfacial waves from quasi-2D to fully 3D. The inlet gas turbulence intensity has a strong impact on the longitudinal instability. The dominant frequency and the spatial growth rate of the longitudinal instability are found to increase with the inlet gas turbulence intensity. The vertical interfacial motion induces Rayleigh-Taylor instability in the transverse direction. The dominant transverse wavenumber, scaling with the longitudinal frequency, also increases with the inlet gas turbulence intensity. Eventually, the sheet breakup dynamics and the statistics of the droplets formed also change accordingly. |
Monday, November 22, 2021 2:41PM - 2:54PM |
M22.00008: Numerical and experimental investigation of jet atomization at low We number toufik saouchi Dispersed phase flows are widely observed in industrial and everyday life applications, studying their characteristics is essential for controlling and optimizing. |
Monday, November 22, 2021 2:54PM - 3:07PM |
M22.00009: Burning dynamics of graphene oxide doped diesel droplets Sepehr Mosadegh, Mohammad H Aboonasr Shiraz, Colin van der Kuur, Mohammad Arjmand, Sina Kheirkhah Burning dynamics of graphene oxide (GO) doped diesel droplets are investigated experimentally. The experiments are performed for diesel droplets doped with 0, 0.001, 0.005, 0.01, and 0.02% by mass of GO. A high-speed shadowgraphy technique, with imaging acquisition frequency and resolution of 2000 Hz and 21 μm, is employed. All tested droplets feature atomization, which starts at about 20 to 30% of the droplet lifetime. The onset of atomization advances with increasing the doping concentration. Prior to atomization, a shell of aggregates is formed immediately after ignition and breaks down as a result of recirculatory flow inside the droplets. Once atomization starts, several bubbles are formed inside the droplets and their surfaces become significantly corrugated. Analysis of the shadowgraphy images shows that the frequency of the bubble formation and the intensity of the droplet surface corrugations are positively and negatively related to the doping concentration, respectively. Overall, the results show that the addition of GO to diesel increases the droplet burning rate, which is of interest for industrial applications. |
Monday, November 22, 2021 3:07PM - 3:20PM |
M22.00010: Evaporation of droplets in a turbulent jet Mogeng Li, Detlef Lohse, Sander G Huisman We experimentally investigate the evaporation and dispersion of liquid droplets in a turbulent air flow. Droplets with diameters of the order of a few micrometers are produced by a spray nozzle and then injected into a homogeneous isotropic turbulence field, which is generated in a purpose-built enclosed dodecahedron chamber. The chamber has an axial fan mounted on each vertex, and it is capable of generating a homogeneous isotropic turbulence field with a Reynolds number based on Taylor microscale up to 160. The ambient temperature and relative humidity in the chamber are carefully controlled. Droplet sizes and velocities at various background turbulence intensity levels are measured by Phase Doppler Anemometry and Interferometric Particle Imaging. The evaporation of droplets will be studied from both Eulerian and Lagrangian perspectives, which will be linked to the mixing of the humid droplets-containing jet with dry ambient air. These results will lead to a deepened understanding of how turbulence affects the evaporation of droplets by modifying the scalar vapour mass field. |
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