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 G24: Experimental Methods III: Lasers, Particle Tracking, PIVExperimental
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Chair: Brian Thurow, Auburn University Room: 703 |
Monday, November 20, 2017 10:35AM - 10:48AM |
G24.00001: Two-Photon Absorption Based Nanoscopic Velocimeter Audrey Wang, Akrm Abdalrahman, Jianyu Deng, Guiren Wang Most velocimeters in micro/nanofluidics rely on particles as flow tracers, such as micro Particle Image Velocimetry ($\mu $PIV). However, for many microflows, such as electrokinetic and near wall flow, magnetophoresis, acoustophoresis, photophoresis and thermophoresis, particles have different velocity from their surrounding fluids. Although most molecular tracer based velocimeters can use neutral dye to measure average velocity, their temporal and spatial resolution are limited. Stimulated emission depletion (STED) based laser-induced fluorescence photobleaching anemometer (LIFPA), i.e. STED-LIFPA has achieved 70 nm spatial resolution. However, STED nanoscopy is very complicated for most users. Here we developed a two--photon absorption LIFPA (TP-LIFPA), which is relatively easier to operate. TP-LIFPA can take advantage of the two--photon microscopy to increase spatial resolution. We use a femtolaser to excite a dye. A microcapillary tube is used to test the feasibility of TP-LIFPA. TP-LIFPA can successfully measure the velocity profile in the capillary. The resolution of TP-LIFPA is estimated to be about 90 nm. The work indicates TP-LIFPA is a new promising nanoscopic velocimeter for interfacial flows, especially within 100 nm at the interfacial area between two phases in the future. [Preview Abstract] |
Monday, November 20, 2017 10:48AM - 11:01AM |
G24.00002: Development of a low-cost multiple diode PIV laser for high-speed flow visualization Raj Bhakta, Michael Hargather Particle imaging velocimetry (PIV) is an optical visualization technique that typically incorporates a single high-powered laser to illuminate seeded particles in a fluid flow. Standard PIV lasers are extremely costly and have low frequencies that severely limit its capability in high speed, time-resolved imaging. The development of a multiple diode laser system consisting of continuous lasers allows for flexible high-speed imaging with a wider range of test parameters. The developed laser system was fabricated with off-the-shelf parts for approximately {\$}500. A series of experimental tests were conducted to compare the laser apparatus to a standard Nd:YAG double-pulsed PIV laser. Steady and unsteady flows were processed to compare the two systems and validate the accuracy of the multiple laser design. PIV results indicate good correlation between the two laser systems and verifies the construction of a precise laser instrument. The key technical obstacle to this approach was laser calibration and positioning which will be discussed. [Preview Abstract] |
Monday, November 20, 2017 11:01AM - 11:14AM |
G24.00003: Comparison of a simulated velocity profile of a turbulent boundary layer with measurements obtained by Femtosecond Laser Electronic Excitation Tagging (FLEET) Matthew New-Tolley, Yibin Zhang, Mikhail Shneider, Richard Miles Accurate velocimetry measurements of turbulent flows are essential for improving our understanding of turbulent phenomena and validating numerical approaches. Femtosecond Laser Electronic Excitation Tagging (FLEET) is an unseeded molecular tagging method for velocimetry measurements in flows which contain nitrogen. A femtosecond laser pulse is used to ionize and dissociate nitrogen molecules within its focal zone. The decaying plasma fluoresces in the visible and infrared spectrum over a period of microseconds which allows the displacement of the tagged region to be photographed to determine velocity. This study compares the experimental and numerical advection of the tagged region in a turbulent boundary layer generated by a supersonic flow over a flat plate. The tagged region in the simulation is approximated as an infinitely thin cylinder while the flow field is generated using the steady state boundary layer equations with an algebraic turbulence model. This approximation is justified by previous computational analyses, using an unsteady three-dimensional Navier-Stokes solver, which indicate that the radial perturbations of the tagged region are negligible compared to its translation. [Preview Abstract] |
Monday, November 20, 2017 11:14AM - 11:27AM |
G24.00004: Experimental study of permeability effects in a smooth-wall turbulent boundary layer Taehoon Kim, Gianluca Blois, James Best, Kenneth Christensen In natural and industrial flow systems, the flow is often bounded by a surface that can be both permeable and rough (e.g. river beds, bed reactors). In such scenarios, the wall boundary condition is complex as it involves both slip and penetration, which together induce significant structural modifications of the overlying flow due to momentum exchange across the wall interface. The current investigation explores the role of the wall permeability in such flows with no topographic effect from the wall. The present wall model was constructed by five layers of cubically arranged spheres ($d=$25.4mm, where $d$ is a diameter) providing 48{\%} of porosity. Surface topography was removed by cutting half of a diameter on the top layer of spheres to render the flow surface smooth and highlight the impact of the permeability on the overlying flow. An impermeable smooth wall was also considered as a baseline of comparison for the permeable wall flow. High-resolution PIV measurements were performed in the streamwise-wall-normal (x-y) plane and refractive-index matching was employed to optically access the flow within the permeable wall. A double averaging method based on the first-order velocity statistics was used to assess the global representation of the flow influenced by wall permeability across the overlying boundary layer. [Preview Abstract] |
Monday, November 20, 2017 11:27AM - 11:40AM |
G24.00005: On turbulence measurements in pipe flow with positron emission particle tracking Cody Wiggins, Roque Santos, Nitant Patel, Arthur Ruggles Positron Emission Particle Tracking (PEPT) is emerging as a measurement technique for flow in granular media and material processing equipment and is of interest to experimental fluid dynamics as it offers the potential for the study of turbulent flows in apparatuses lacking optical access. Here, PEPT is explored as a viable means of Lagrangian particle tracking for turbulence studies. A PEPT study of turbulent water flow (Reynolds number 20,000) in a pipe of circular cross section is performed. Measured trajectories are used to examine Eulerian and Lagrangian turbulence quantities of interest. It is observed that measured Reynolds stresses and acceleration statistics are similar to those previously detailed. Measurement uncertainties are seen to adversely affect measured structure functions, and a correction is attempted. Lagrangian velocity structure functions are seen to show significant deviation from Kolmogorov-like scaling. Results obtained require further study via experiment and simulation to determine if any observations are artifacts of the PEPT technique. [Preview Abstract] |
Monday, November 20, 2017 11:40AM - 11:53AM |
G24.00006: Flow induced by a femtosecond laser filament Shahram Pouya, Manoochehr Koochesfahani Propagation of femtosecond pulsed lasers is of interest to a variety of applications in science and engineering. These laser sources also provide an attractive tool for molecular tagging velocimetry in air (e.g. FLEET). However, high power density of such short pulse lasers can potentially lead to flow perturbations. In this work we present PIV measurements in air around a high repetition rate (1 KHz) focused femtosecond laser beam and quantify the level of flow disturbances that it introduces in its vicinity. Results are shown for various pulse energy levels and the time scale for generation of flow disturbance. These results provide information about the measurement constraints when using femtosecond lasers in molecular tagging velocimetry. [Preview Abstract] |
Monday, November 20, 2017 11:53AM - 12:06PM |
G24.00007: Laser-Induced Fluorescence, Particle Tracking Velocimetry And Infrared Thermography For The Investigation Of Spatiotemporally Resolved Heat-Transfer In Thin Liquid-Film Flows Christos Markides, Alexandros Charogiannis Laser-induced fluorescence (LIF), particle tracking velocimetry (PTV) and infrared thermography (IRT) are employed towards the detailed study of the hydrodynamic characteristics and heat-transfer performance of harmonically-excited film-flows falling over a resistively heated glass-substrate. PLIF is used to recover space- and time-resolved film-heights, PTV to obtain velocity data across the flow, and IRT to measure the temperature of the gas-liquid interface. The liquid Kapitza number is set to $Ka = 180$, the Reynolds number is varied in the range $Re = 20 - 75$, the heat-flux at the wall is varied between $\dot q = 1.5$ and 3 $\textrm{W cm}^{-2}$, and the forcing-frequency is varied between $f_\textrm{w} = 7$ and 17 Hz. Complementary data are obtained for the same flow $Re$ and $f_\textrm{w}$ under isothermal conditions. Using the IRT data and knowledge of the local solid-liquid interface temperature, we also recover heat transfer coefficients (HTCs), and link those to the hydrodynamics of the examined films. Towards that end, we generate highly localized flow and heat-transfer data along the waves by employment of phase-locked averaging, along with film-height, velocity, flow-rate and HTC time-series. [Preview Abstract] |
Monday, November 20, 2017 12:06PM - 12:19PM |
G24.00008: A LIF-PIV investigation of turbulence induced by sprays Dennis Van der Voort, Nico Dam, Willem van de Water, Herman Clercx During the breakup of a high-speed liquid jet, it drags along and mixes the air surrounding it, creating turbulence. This turbulence can, in turn, influence the dispersion of the droplets in the resulting spray. Very little is known about the small-scale characteristics of the ambient turbulent flow. This work investigated spray-induced turbulence using (gas-phase) laser-induced fluorescent tracer particle image velocimetry (LIF-PIV), which suppresses the strong light scattering of jet and droplets on the images. The results for both a heptane (h) and water (w) spray (135 m/s and 125 m/s respectively) show that the heptane spray generates stronger turbulence due to the difference in breakup between the two fluids. Using a large-eddy estimation, carefully compensating for the finite size of the PIV windows, the dissipation rate $\epsilon$ and the small-scale turbulence characteristics are estimated as $\epsilon_{\mathrm{h}} =$ 190$\pm$25 m$^{2}$s$^{-3}$, $\epsilon_{\mathrm{w}} =$ 120$\pm$30 m$^{2}$s$^{-3}$, Re$_{\lambda,\mathrm{h}} =$ 380$\pm$40, Re$_{\lambda,\mathrm{w}} =$ 290$\pm$40, $\eta_{\mathrm{h}}$ = 65$\pm$3 $\mu$m, and $\eta_{\mathrm{w}}$ = 75$\pm$5 $\mu$m. We will discuss the influence of the turbulent fluctuations in the surrounding air on the dispersion of droplets. [Preview Abstract] |
Monday, November 20, 2017 12:19PM - 12:32PM |
G24.00009: The 80 eyes PIV Akiyoshi Maekawa, Jun Sakakibara In order to reduce measurement error and expand the dynamic range of PIV, we developed a ellipsoidal polyhedral mirror placed between camera and flow target to capture images of identical particles from $n$ ($=$80 in maximum) different directions. The 3D particle positions were determined from the ensemble average of $_{n}$C$_{\mathrm{2}}$ intersecting points of a pair of line of sight back-projected from a particle found in two images extracted from $n$ images. We hypothesized that the error of measured particle displacement is reduced by a factor of $1/\sqrt n $ thanks to the central limit theorem. A rigid-body rotating flow and a turbulent pipe flow were measured by the above method. In the former measurement, bias error and random error fell into a range of ± 0.02 pixels and 0.025 to 0.05 pixels, respectively, and the random error decreases in proportion to~$1/\sqrt n $. In the latter measurement in which the measured value was compared to DNS, the bias error was reduced, and the random error also decreases in proportion to~$1/\sqrt n $ when the particle displacement was relatively small. When the particle displacement was larger, the random error was difficult to estimate, since a discrepancy of the experiment and DNS results might be dominant. [Preview Abstract] |
Monday, November 20, 2017 12:32PM - 12:45PM |
G24.00010: Analysis of slippery droplet on tilted plate by development of optical correction method Han Seo Ko, Yeonghyeon Gim, Sung Ho Choi, Dong Kyu Jang, Dong Kee Sohn Because of distortion effects on a surface of a sessile droplet, the inner flow field of the droplet is measured by a PIV (particle image velocimetry) method with low reliability. In order to solve this problem, many researchers have studied and developed the optical correction method. However, the method cannot be applied for various cases such as the tilted droplet or other asymmetric shaped droplets since most methods were considered only for the axisymmetric shaped droplets. For the optical correction of the asymmetric shaped droplet, the surface function was calculated by the three-dimensional reconstruction using the ellipse curve fitting method. Also, the optical correction using the surface function was verified by the numerical simulation. Then, the developed method was applied to reconstruct the inner flow field of the droplet on the tilted plate. The colloidal droplet of water on the tilted surface was used, and the distorted effect on the surface of the droplet was calculated. Using the obtained results and the PIV method, the corrected flow field for the inner and interface parts of the droplet was reconstructed. Consequently, the error caused by the distortion effect of the velocity vector located on the apex of the droplet was removed. [Preview Abstract] |
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