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 L37: Multiphase Spray |
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Chair: Dorrin Jarrahbashi, Texas A&M University Room: 619 |
Monday, November 25, 2019 1:45PM - 1:58PM |
L37.00001: Verification and Validation of a Continuous Adjoint Formulation for Liquid-Gas Flows Lam Vu, Alexandru Fikl, Daniel Bodony, Olivier Desjardins Atomization appears in a variety of engineering applications such as fuel sprays for combustion engines and powder production for additive manufacturing. The capability to perform systematic spray control is paramount to the development of atomization technologies. However, spray control represents a major challenge due, in part, to the large parameter space and to the lack of reduced order models. Consequently, spray control has traditionally been conducted based on trial and error. Spray control problems can be approached systematically by posing them as an optimization problem where the goal is to choose a set of control parameters that maximize a user-defined spray metric, the cost function. Solving this optimization problem through gradient-descent requires the evaluation of the gradient of the cost function with respect to the control parameters, which is acquired through an adjoint formulation. In this study, we verify and validate our implementation of a continuous adjoint formulation for liquid-gas flows. In particular, we confirm that the gradient calculated from the adjoint formulation agrees with the one calculated through finite differencing. Finally, we explore the application of the liquid-gas flow adjoint formulation to the control of sprays. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L37.00002: Tracking droplet breakup in homogenous isotropic turbulence Alexander Bussmann, Jonas Buchmeier, Michael Dodd, Ivan Bermejo-Moreno A methodology is introduced to study the dynamics of fluid interfaces in multiphase flows, emphasizing their breakup and coalescence. The algorithm tracks surfaces, here obtained by isocontouring an interface-describing scalar field (e.g., VOF) from a time series of volumetric snapshots. Physical and geometric information of the surfaces is used to find correspondences in a higher-dimensional space, from which events are derived to describe the interactions among surfaces at consecutive time instances. Correspondences and events are filtered based on physical realizability, accounting for geometric constraints between consecutive time instances, as well as temporal constraints on the relations between surfaces in previous tracking steps. Resulting events are used to map the time evolution of all surfaces and their interactions into a graph, which is then queried to retrieve information on the dynamics of the fluid interfaces. The methodology is applied to a DNS dataset of droplet breakup in homogeneous isotropic turbulence. Emphasis is placed on the statistics of split and merge events, the lifetime of surfaces, and their geometric evolution in relation to the background flow fields. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L37.00003: Physics of liquid break-up in a two-fluid coaxial atomizer forced by an external acoustic field Peter Dearborn Huck, Rodrigo Osuna-Orozco, Nathanael Machicoane, Alberto Aliseda We investigate acoustic forcing as a means of actuation in the formation of liquid drops and ligaments at the interface between a low momentum liquid cylinder and a high momentum coaxial gas jet. A canonical two-fluid co-axial atomizer is experimentally investigated, at a wide range of gas to liquid momentum ratios, but within the high Weber number break-up limit. The liquid cylinder is placed at the velocity of an acoustic waveguide where the second traverse mode of the cavity is excited. Anemometry measurements show disturbances in the boundary layer at the nozzle’s orifice, but the self-similar nature of the gas-phase jet is retained in the mid field. Phase Doppler Interferometry measurements of the droplet size, velocity and number density confirm that acoustic forcing in the near field is effective at enhancing atomization (the Sauter Mean Diameter decreases by 25$\%$), and at modifying the dispersion of the droplet phase in the mid-field (increased radial extent of the spray). High-speed shadowgraphy, capable of resolving 15-micrometer droplets, illustrate the physics of atomization under a high-frequency acoustic field and help support real-time actuation in a feedback control implementation. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L37.00004: Swirl Optimization to Maximize Spray Angle from a Coaxial Airblast Atomizer Scott A. Zmuda, Timothy B. Morgan, Julie K. Bothell, Theodore J. Heindel Liquid sprays play a key role in many engineering processes (e.g., food processing, coating and painting, 3D printing, fire suppression, combustion systems, etc.). One method of forming a spray is through a coaxial airblast atomizer in which a liquid stream is surrounded by a gas jet. Adding swirl to the gas jet can modify the resulting spray angle. This study completes a parametric study over a range of gas and liquid flow rates, momentum ratios, and swirl percentages, to identify those conditions that maximize spray angle. The spray angle is determined by back-illuminating the spray with an LED light panel to form a shadow of the resulting spray. A high-speed camera is then used to capture a series of successive images. Image analysis is then used to determine an average spray angle. It is shown that the swirl percentage for the maximum spray angle is a function of the flow conditions. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L37.00005: Particle-droplet interaction in turbulent channel flow Arash Hajisharifi, Cristian Marchioli, Alfredo Soldati We examine the interaction between small (sub-Kolmogorov) slightly inertial particles and large deformable droplets in turbulent channel flow. To simulate such solid-liquid-liquid flow, we exploit a Eulerian-Lagrangian methodology based on direct numerical simulation of turbulence, coupled with a Cahn-Hilliard Phase Field Model to capture the interface dynamics and Lagrangian tracking to compute particle trajectories. We model the particle-interface interaction via a capillary force based on the liquid-liquid surface tension and on the local interface curvature. This force gives a potential well that drives particle accumulation on the droplet interface, which acts as particle adsorber. We quantify particle-interface interaction in a simplified situation where the droplets have the same density and viscosity of the carrier liquid (mimicking a water-oil emulsion), and particles are one-way coupled with the fluids. Particle-induced deformation of the interface and the effect of gravity are neglected. Preliminary simulations indicate that particles tend to aggregate in regions of the interface characterized by high curvature, and that this tendency is modulated by particle inertia: The higher the inertia of the particles, the stronger the tendency to escape from the interface. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L37.00006: Multi-Scale Investigation of Spray Droplets Issued in a Turbulent Background Douglas Carter, Roumaissa Hassaini, Filippo Coletti We present time-resolved planar measurements of an upward-facing hollow cone spray with simultaneous large and small scale fields of view. The measured mean droplet diameter of 50um for the spray issued into both quiescent and turbulent backgrounds is found to correspond to Stokes numbers approaching order one, indicating that the droplets act as non-ideal flow tracers. The dynamics of the drops are investigated by particle tracking velocimetry (PTV) to educe the instantaneous droplet motion and particle image velocimetry (PIV) to extract the~correlated~droplet motion in the far field of the spray. It is found that the droplets issued into quiescent air exhibit greater random uncorrelated motion (RUM) compared to the droplets in a turbulent background, implying that the turbulent eddies prevent the droplets from moving ballistically. This is also reflected by the lesser drop in the Eulerian autocorrelations at small separations for droplets issued into a turbulent background as well as the general increase in the magnitude of the Lagrangian autocorrelations. These results provide novel insight into the motion of inertial droplets in a turbulent gas, and have implications for the numerical modeling and control of liquid sprays. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L37.00007: Experimental Analysis of Spray Atomization for Targeted Deposition of Nanoparticles Shadi Shariatnia, Farzad Poursadegh, Amir Asadi, Dorrin Jarrahbashi Targeted delivery of nanoparticles has a wide range of applications in electronics, pharmaceuticals, and advanced manufacturing. A novel process that deposits cellulose nanocrystals (CNC) on a silicon wafer has been introduced. CNC-containing droplets were generated by injecting aqueous suspension of CNC through an air-atomized nozzle, where a high-pressure liquid jet undergoes severe instabilities due to the large pressure drop between the injector and ambient atmospheric conditions. High-speed diffuse back illumination (DBI), laser diffraction techniques and scanning electron microscopy (SEM) are employed to visualize and quantify the effects of spray parameters on nanoparticles distribution. The liquid jet breaks up into ligaments that later form large number of micron-size droplets at a small distance downstream of the nozzle that further evaporate and release nanoparticles on the targeted surface. Controlling process parameters such as pressure and temperature of the injected and ambient medium, characteristics of the nozzle and rheology of the aqueous nanoparticle suspension directly impacts the droplet size distribution and hence dispersion and distribution of nanoparticles. [Preview Abstract] |
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