Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session A1: Jets: Formation and ImpingingShear layer
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Chair: Emre Turkoz, Princeton University Room: 401 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A1.00001: Sweeping jet for convective heat transfer of a flat plate Tongil Park, Kursat Kara, Daegyoum Kim A fluidic oscillator, which generates unsteady sweeping jet without any actuator and moving parts, has received much attention due to its attractive features: high durability to shock and vibration and no electromagnetic interference. In this work, we apply the fluidic oscillator to improve the performance of convective heat transfer. The sweeping jet impinges vertically on a heated flat plate. By varying Reynolds number and nozzle-to-plate spacing, we experimentally investigate the characteristics of a heat transfer rate of the plate and examine flow fields to find the flow characteristics responsible for enhancing heat transfer. Temperature on the plate was measured with thermocouples, and flow fields were obtained with planar particle image velocimetry. From the flow fields, dominant flow structure is extracted using proper orthogonal decomposition. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A1.00002: Flow field characteristics of impinging sweeping jets: TR-PIV measurement. Xin Wen, Di Peng, Yingzheng Liu, Hui Tang Influence of Reynolds number of sweeping jets on its impinging flow fields was extensively investigated in a water tank. Toward this end, a fluidic oscillator was specially designed to produce spatially sweeping jets which imping on a flat plate. Six Reynolds numbers were tested by controlling the supply flow rate of the fluidic oscillator. Impinging flow fields were captured by time-resolved Particle Image Velocimetry (TR-PIV) measurement. Reference signals were extracted from the flow fields for phase reconstruction. The oscillating flow fields with super-harmonic frequency at different regions were discussed in term of the phase-averaged velocity, vorticity and turbulent velocity. Dynamic mode decomposition (DMD) was used to capture the most-energetic flow patterns with distinct frequencies. By projecting the phase-averaged flow fields onto a reduced basis of DMD modes, the phase correlation between the distinct flow patterns were analyzed under different Reynolds numbers. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A1.00003: Numerical simulation of conjugate heat transfer in liquid jet impingement on a moving plate Jaewon Lee, Gihun Son Numerical simulation is performed for a conjugate heat transfer in liquid jet impingement on a moving hot plate. The associated flow and cooling characteristics, including forced convection and film boiling in the fluid region as well as conduction in the moving solid region, are investigated by solving the conservation equations of mass, momentum, energy, turbulent kinetic energy and dissipation rate in the liquid, gas and solid phases. A vapor film model, which is based on the energy balance between the liquid and vapor phases as well as the fluid and solid phases, is implemented to predict the heat flux at the fluid-solid interface, instead of using the existing model based on the empirical coefficients. The numerical results for various initial conditions of 800°C to the Leidenfrost temperature demonstrate that cooling performance and temperature variation of the plate significantly depend on the heat transfer modes of forced convection and film boiling. When a plate is deformed, the local variation of heat flux is influenced by the plate deformation. The effects of jet velocity, jet temperature and plate deformation on the conjugate heat transfer are also investigated. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A1.00004: Particle-Laden Liquid Jet Impingement on a Moving Substrate Hatef Rahmani, Sheldon Green The impingement of high-speed jets on a moving substrate is salient to a number of industrial processes such as surface coating in the railroad industry. The particular jet fluids studied were dilute suspensions of neutrally buoyant particles in water-glycerin solutions. At these low particle concentrations, the suspensions have Newtonian fluid viscosity. A variety of jet and surface velocities, solution properties, nozzle diameters, mean particle sizes, and volume fractions were studied. It was observed that for jets with very small particles, addition of solids to the jet enhances deposition and postpones splash relative to a particle-free water-glycerin solution with the same viscosity. In contrast, jets with larger particles in suspension were more prone to splash than single phase jets of the same viscosity. It is speculated that the particle diameter, relative to the lamella thickness, is the key parameter to determine whether splash is suppressed or enhanced. An existing splash model for single phase liquid jets was found to be in good agreement with the experimental results, provided that the single fitting parameter in that model is a function of the particle size, volume fraction, and surface roughness. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A1.00005: Characterization of two-dimensional impinging jets Xueqing Zhang, Serhiy Yarusevych, Sean D. Peterson The development of a slot jet impinging on a plate is investigated experimentally using 2D-PIV. The study is performed for two jet Reynolds numbers, Re = 3000 and 6000, and four jet orientation angles relative to the wall ($\theta = 90^\circ, 60^\circ, 45^\circ, 30^\circ$), with the nozzle-to-plate spacing fixed at four slot widths. Within the range of impingement angles considered, the flow is characterized by a stagnation region, followed by a region of flow reorientation into a wall jet. Shallower impingement angles lead to a smaller stagnation region and larger displacement of the stagnation point from the geometric projection of the jet centreline. Increasing Re or decreasing $\theta$ results in a reduction of the growth rate of jet half-width in the wall jet region. Coherent structures form in the jet shear layers and merge throughout the reorientation and initial wall jet regions. In all cases considered, POD is employed to identify the coherent structures and quantify their salient characteristics. The results identify the relative contribution of shear layer rollers and merged vortices to the overall turbulent kinetic energy, and elucidate the effect of Reynolds number and impingement angle on the development of coherent structures. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A1.00006: Experimental evaluation of a system of multiple angled impinging jets in a turbulent water flow Jean-Philippe Delaforge, Michael Benson, Bret Van Poppel, Christopher Elkins Impinging jets are frequently used for applications requiring high heat transfer rates. Effective area coverage is obtained by grouping these jets spatially, though such flows are more challenging to measure except in an averaged sense, and simulations historically fail to accurately predict the behavior in the vicinity of the impingement zone. In this work, we present results from an experimental technique, Magnetic Resonance Velocimetry (MRV), which measures the three components of three-dimensional time-averaged velocity field with two impinging jets. The geometry considered in this study includes two circular jet angled at 45 degrees and impinging on a flat plate, with a separation of approximately seven jet diameters between the jet exit and the impingement location. Two flow conditions are considered, with Reynolds numbers of roughly 8,000 and 14,000. Measurements from the MRV experiment are compared to predictions from Reynolds Averaged Navier-Stokes (RANS) simulations, thus demonstrating the utility of MRV for validation of numerical analyses of impinging jet flow. [Preview Abstract] |
(Author Not Attending)
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A1.00007: Characterizing Wall Shear Stress from Underexpanded Impinging Jets Patrick Fillingham Normalized wall shear stress is characterized for underexpanded axisymmetric impinging jets. The flow field and wall shear stress are calculated using Computational Fluid Dynamics. A normally impinging jet is modeled with varying impingement height, nozzle diameter, fluid properties and nozzle pressure ratios. Schlieren photography is used to visualize the density gradient of the flow field while pressure sensitive paint is used to determine pressure profile of the impingement surface; these experiments are used to validate the CFD. A \textit{Dimensionless Jet Parameter} (DJP) is developed to characterize magnitude and location of maximum shear stress as a function of nozzle parameters. A local Reynolds number is calculated and characterized as a function of jet parameters. This local Reynolds number is used to develop relationships for wall shear stress at all locations along the impingement surface. Two distinct regimes, with separate relationships for wall shear stress and local Reynolds number, are present along the impingement surface; the near impingement region and the down plate region. The culmination of this work allows for the prediction of wall shear stress and local Reynolds Number in the compressible boundary layer from underexpanded impinging jets based upon nozzle flow conditions as well as local flow measurements. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A1.00008: Focused liquid jet formation from micrometer-sized cavities using impulsive boundary deformation Emre Turkoz, Luc Deike, Craig B. Arnold Laser-induced jetting is an area of interest for jet-based printing and dispensing techniques. In this study, we are examining the flow focusing and subsequent high-speed jet formation from micrometer-sized cavities on a polymer thin film. A nanosecond laser pulse is absorbed within a polymer layer which hosts micrometer-sized cavities that are introduced using a picosecond laser and coated with the ink to be printed. The absorption of the laser pulse leads to impulsive boundary deformation that induces jet formation from the ink which is located inside the cavity. Due to the micrometer size of cavities, surface tension effects are enhanced and the formed jets are very thin due to the resulting flow focusing effect at the concave ink-ambient air interface. Furthermore, droplets generated from the induced thin jets have small diameter values that could not be obtained without the flow-focusing effect. A time-resolved imaging setup along with direct numerical simulations of the two-phase Navier-Stokes equations are used to examine the underlying physics and effects of the experiment parameters to the resulting jet formation. The experimental conditions such as the cavity size and laser energy are examined for single-drop ejections, which are desirable for high-resolution printing. [Preview Abstract] |
Sunday, November 19, 2017 9:44AM - 9:57AM |
A1.00009: Laser-Induced Forward Transfer of Viscoplastic Fluids Martin H. Klein Schaarsberg, Maziyar Jalaal, Claas Willem Visser, Detlef Lohse Laser-Induced Forward Transfer (LIFT) is a method of additive manufacturing on small scales with a wide variety of applications in the fabrication of flexible electronics, optics, and living tissues. In LIFT, a single laser pulse is focused onto a thin film of the target material, which ultimately leads to the ejection of a droplet. We aim to develop better understanding of the effect of the rheological properties of non-Newtonian fluids and pastes on the LIFT ejection mechanism. We investigate the violent fragmentation and jetting of viscoplastic fluids with high-speed imaging. [Preview Abstract] |
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