Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session L3: Multiphase Flows: Atomization and Droplets |
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Chair: Olivier Desjardins, Cornell University Room: 23B |
Monday, November 19, 2012 3:35PM - 3:48PM |
L3.00001: Droplet Jumping Induced by Focused Surface Acoustic Wave on Superhydrophobic Surface Marten Darmawan, Kwangsun Jeon, Doyoung Byun We investigate the droplet jumping phenomena that are induced by focused surface acoustic wave on superhydrophobic surface. The utilization of an identical pair of single phase unidirectional transducers (SPUDTs) leads to the focusing of acoustic wave energy on a small region between them. This focused energy gives a very high acceleration as well as rapid interface destabilization to the liquid droplet and thus derives the jumping phenomenon once surpasses some Weber number's threshold value. We intriguingly investigate the effect of the small contact area of droplet on superhydrophobic surface, which is generated by using plasma treatment, to the droplet jetting phenomena and how it deforms under this circumstance. Furthermore, a parametric study, i.e. varying acoustic energy power, volume of droplet and degree of arc SPUDT, is also performed to investigate their effect on the elongated jumping droplet. [Preview Abstract] |
Monday, November 19, 2012 3:48PM - 4:01PM |
L3.00002: Convective Air Mass Transfer in Submerged Superhydrophobic Surfaces Christina A. Barth, Mohamed A. Samaha, Hooman Vahedi Tafreshi, Mohamed Gad-el-Hak Under pressure and flowing water, air entrapped in submerged superhydrophobic coatings eventually dissolve into the water. We analyze from first principles a simple mass transfer problem. We introduce an {\em effective} slip to a Blasius boundary layer, and solve the hydrodynamic as well as the mass transfer equations. Similarity solutions are found for both systems of equations. We then solve the two-dimensional problem of alternating free-shear and no-slip regions. This situation simulates spanwise microridges. The second problem has no similarity solution but is solvable using approximate integral methods. A mass-transfer correlation is achieved and relates the surface geometry (or gas area fraction) to the effective slip. The analytical results are compared to numerical simulations obtained via the FLUENT software for the laminar Navier--Stokes equations. Longevity, or time-dependent hydrophobicity, could be estimated for the simple laminar, flat-plate geometry investigated, and is compared to experimental results. [Preview Abstract] |
Monday, November 19, 2012 4:01PM - 4:14PM |
L3.00003: ABSTRACT WITHDRAWN |
Monday, November 19, 2012 4:14PM - 4:27PM |
L3.00004: Efficient High-Fidelity Simulation of Pressure Swirl Injection Mark Owkes, Olivier Desjardins Atomization of hydrocarbon fuels is of critical importance to air-breathing, liquid-fueled internal combustion engines used in the transportation sector. While atomizers can take widely different forms and operate under a wide range of conditions, pressure swirl atomizers are essential as they represent the main component of most air-blast spraying systems for gas turbines. Experimental investigations of pressure swirl injectors are challenging due to their often-intricate geometry, and due to the formation of a conical liquid sheet that complicates optical access to the central injector region. Hence, numerical simulations have the potential to shed light on the physics of such injectors. To tackle such a task computationally, methods are needed for efficiently handling of complex geometries, and robustly and conservatively handle high-density ratio turbulent two-phase flows. In this work, a computational study of pressure swirl injection is presented based on an efficient approach that combines ideas from immersed boundary, level set, volume of fluid, and ghost fluid methods. The flow dynamics within the injector as well as the spray cone are discussed. [Preview Abstract] |
Monday, November 19, 2012 4:27PM - 4:40PM |
L3.00005: High fidelity simulation of transcritical injection Marios Soteriou, Hui Gao, Xiaoyi Li, Dustin Davis Transcritical injection of a multi-component fluid occurs in many practical applications such as diesel and rocket engines. In this type of injection a liquid fuel at a supercritical pressure but subcritical temperature, is introduced into an environment where conditions are supercritical. The convoluted physics of the transition from the subcritical to the supercritical state is linked to thermodynamic property variations and poses challenges to numerical simulation. For example, the temporary presence of surface tension implies that both the subcritical liquid-vapor interface and the transition boundary to supercritical fluid need to be captured. In this work, numerical simulation of a binary system of a subcritical liquid injecting into a supercritical, quiescent gaseous environment is performed. A coupled level set and volume of fluid method is adopted to capture the liquid-vapor interface, across which the continuity of mass and energy fluxes is preserved. The fluid state over the range of subcritical liquid to supercritical fluid is determined by incorporating the Peng-Robinson equation of state. To efficiently account for the sharp changes in properties near the liquid-vapor interface and the transition boundary to supercritical fluid, an adaptive mesh refinement technique is employed. Analysis of results focuses on the impact of vanishing surface tension as conditions transition from sub-critical to supercritical. [Preview Abstract] |
Monday, November 19, 2012 4:40PM - 4:53PM |
L3.00006: ABSTRACT WITHDRAWN |
Monday, November 19, 2012 4:53PM - 5:06PM |
L3.00007: Isogeometric analysis of drop deformation in isoviscous shear flow Amin Ahmadi Joneidi, Clemens Verhoosel, Patrick Anderson We use the Boundary Integral Method (BIM) to study the deformation of a drop in iso-viscous shear flow. Traditionally the drop surface is represented by a linear triangular mesh. The novelty of this work compared to prior studies is applying Isogeometric Analysis (IGA) to define the drop interface. In this method splines are used as smooth shape functions to create the surface instead of the traditional non-smooth triangular surface. This makes IGA applicable in the case when the physics at the interface becomes more complicated, for example if the deformation of a red blood cell or a vesicle is investigated; these involve higher-order surface gradients in the force jump across the interface. For the iso-viscous drop it is observed that the drop deforms and deviates from the initial spherical shape and orients itself in the fixed direction. Different values of the capillary number -which is the measure of the ratio between viscous and surface tension forces- have been studied and the results match very well with traditional BIM. IGA results for more complex interfacial force jumps are discussed. [Preview Abstract] |
Monday, November 19, 2012 5:06PM - 5:19PM |
L3.00008: Impact of Liquid Fuel Boundary Condition and Nozzle Geometry on Liquid Jet in Crossflow Atomization Sina Ghods, Marcus Herrmann The atomization of a liquid jet by a high speed cross-flowing gas has many applications such as gas turbines and augmentors. The mechanisms by which the liquid jet initially breaks up, however, are not well understood. Experimental studies suggest the dependence of spray properties on operating conditions and nozzle geometry. Detailed numerical simulations can offer better understanding of the underlying physical mechanisms that lead to the breakup of the injected liquid jet. In this work, we present detailed numerical simulation results of turbulent liquid jets injected into turbulent gaseous cross flows for different liquid fuel boundary conditions and injector geometries. We employ a finite volume, balanced force fractional step flow solver to solve the Navier-Stokes equations coupled to a Refined Level Set Grid method to follow the phase interface. To enable the simulation of atomization of high density ratio fluids, we ensure discrete consistency between the solution of the conservative momentum equation and the level set based continuity equation by employing the Rescaled Conservative Momentum method. We analyze the impact of liquid jet turbulent fluctuations and injector geometry on different jet properties such as jet penetration and generated drop sizes. [Preview Abstract] |
Monday, November 19, 2012 5:19PM - 5:32PM |
L3.00009: Measurement of liquid film flow on nuclear rod bundle in micro-scale by using very high speed camera system Son Pham, Zensaku Kawara, Takehiko Yokomine, Tomoaki Kunugi Playing important roles in the mass and heat transfer as well as the safety of boiling water reactor, the liquid film flow on nuclear fuel rods has been studied by different measurement techniques such as ultrasonic transmission, conductivity probe, etc. Obtained experimental data of this annular two-phase flow, however, are still not enough to construct the physical model for critical heat flux analysis especially at the micro-scale. Remain problems are mainly caused by complicated geometry of fuel rod bundles, high velocity and very unstable interface behavior of liquid and gas flow. To get over these difficulties, a new approach using a very high speed digital camera system has been introduced in this work. The test section simulating a 3x3 rectangular rod bundle was made of acrylic to allow a full optical observation of the camera. Image data were taken through Cassegrain optical system to maintain the spatiotemporal resolution up to 7 $\mu$m and 20 $\mu$s. The results included not only the real-time visual information of flow patterns, but also the quantitative data such as liquid film thickness, the droplets' size and speed distributions, and the tilt angle of wavy surfaces. These databases could contribute to the development of a new model for the annular two-phase flow. [Preview Abstract] |
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