Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session D27: Experiments: Velocity and Vorticity Measurements |
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Chair: Ahmed Naguib, Michigan State University Room: 308 |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D27.00001: Boundary-Layer Resolved Measurements of a Three-Dimensional Disturbance Using Magnetic Resonance Velocimetry Ahmed Naguib, Florian Wassermann, Daniel Freudenhammer, Sven Grundmann Magnetic Resonance Velocimetry (MRV) is a modern flow diagnostic technique with unique advantages including the ability to efficiently capture volumetric measurements of velocity fields in complex geometry without the need for optical access. In comparison to Particle Image Velocimetry, MRV is substantially underutilized, and hence MRV's strengths and limitations to address a variety of flow configurations is yet to be demonstrated. Investigated in the present work is the viability of MRV to provide boundary-layer-resolved measurements of a 3D disturbance created by a circular cylindrical element protruding from the wall. These measurements are challenging because of the high spatial resolution requirement over a relatively large measurement volume (100 x 100 x 250 mm$^{\mathrm{3}})$, the weak cross-stream disturbance velocities (less than 0.1{\%} of the freesteam velocity), and the difficulties associated with the presence of a wall. Data are acquired using a portable water-flow loop with an acrylic test section placed on the bed of an MRI machine. The cylindrical element is mounted through the test-section's side wall where the boundary layer Reynolds number (Re) is 162 based on displacement thickness. Several element heights are investigated, ranging from a fraction of, to a full boundary layer thickness. The results provide an assessment of the ability of MRV to perform boundary-layer-resolved measurements of weak disturbances. [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D27.00002: Multi-plane Particle Shadow Velocimetry to Quantify Integral Length Scales Jeff Harris, Christine Truong, Steven Hinkle, Kyle Sinding, Tiffany Camp, Arnie Fontaine, Michael Krane, David DeVilbiss Multi-plane PIV has been used for several years to assist in quantifying the integral length scales in turbulent flow. Particle shadow velocimetry (PSV) enables illumination of a volume and is an efficient means of obtaining multi-plane illumination. The combination of two colors in the LED backlight and a dichroic mirror makes possible the imaging of two planes in space without the complexity of aligning two different light sources. The velocity fields obtained in these two vector fields are then correlated to obtain length scales using the definitions in the literature. The length scales and multi-plane measurements are compared with previous studies which used proven measurement methods. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D27.00003: Advances of Fluid-Structure Interaction Measurements by Multi-Pulse Particle Image Velocimeter/Accelerometer Liuyang Ding, Ronald Adrian, Sivaram Gogineni Multi-pulse particle image velocimeter/accelerometer (PIV/A) is recently developed to improve the performance of conventional PIV and expand the application area. A multi-pulse system consisting of four independent lasers and a high-speed CMOS camera is used for fluid-structure interaction measurements. The test section is an oscillating cylinder (Plexiglas) immersed in refractive-index-matching (RIM) solution and supported by two elastic rods. The unsteady flow field with moving cylinder is imaged at a frequency of 16 sets per cycle, with each set containing four fast consecutive frames. The cylinder motion is tracked by image segmentation technique. Fluid instantaneous and phase averaged velocity and acceleration fields are measured by triple- and quadruple-pulse PIV/A, and their results are compared. Furthermore, the fluid force acting on the cylinder is evaluated using multi-pulse PIV/A data with control volume approach. The rod tip deflection is then calculated by Euler-Bernoulli beam theory and the force measurements, and compared with the ground truth showing good measurement accuracy. The simultaneous velocity, acceleration and force measurements provide a great way for understanding the fluid-structure interaction. [Preview Abstract] |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D27.00004: Current collector geometry and mixing in liquid metal electrodes Rakan Ashour, Douglas Kelley Liquid metal batteries are emerging as an efficient and cost effective technology for large-scale energy storage on electrical grids. In these batteries, critical performance related factors such as the limiting current density and life cycle are strongly influenced by fluid mixing and transport of electrochemical species to and from the electrode-electrolyte interface. In this work, ultrasound velocimetry is used to investigate the role of negative current collector location on the induced velocity, flow pattern, and mixing time in liquid metal electrodes. Ultrasound velocity measurements are obtained at a range of operating current densities. Furthermore, a comparison between velocity profiles produced by current collectors with different sizes is also presented. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D27.00005: Holographic measurement of wall stress distribution and 3D flow over a surface textured by microfibers Humberto Bocanegra, Seder Gorumlu, Burak Aksak, Luciano Castillo, Jian Sheng Understanding how fluid flow interacts with micro-textured surfaces is crucial for a broad range of key biological processes and engineering applications including particle dispersion, pathogenic infections, and drag manipulation by surface topology. Existing methods, such as $\mu$PIV, suffers from low spatial resolution and fail to track tracer particle motion very close to a rough surface and within roughness elements. In this paper, we present a technique that combines high speed digital holographic microscopy (DHM) with a correlation based de-noising algorithm to overcome the optical interference generated by surface roughness and to capture a large number of 3D particle trajectories. It allows us to obtain a 3D velocity field with an uncertainty of 0.01{\%} and 2D wall shear stress distribution at the resolution of $\sim$ 65$\mu$Pa. Applying the technique to a microfluidics with a surface textured by microfibers, we find that the flow is three-dimensional and complex. While the microfibers affect the velocity flow field locally, their presence is felt globally in terms of wall shear stresses. The study of effect of microfiber patterns and flow characteristics on skin frictions are ongoing and will be reported. [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D27.00006: Three-dimensional flow measurements in a tesla turbine rotor Thomas Fuchs, Constantin Schosser, Rainer Hain, Christian Kaehler Tesla turbines are fluid mechanical devices converting flow energy into rotation energy by two physical effects: friction and adhesion. The advantages of the tesla turbine are its simple and robust design, as well as its scalability, which makes it suitable for custom power supply solutions, and renewable energy applications. To this day, there is a lack of experimental data to validate theoretical studies, and CFD simulations of these turbines. This work presents a comprehensive analysis of the flow through a tesla turbine rotor gap, with a gap height of only 0.5 mm, by means of three-dimensional Particle Tracking Velocimetry (3D-PTV). For laminar flows, the experimental results match the theory very well, since the measured flow profiles show the predicted second order parabolic shape in radial direction and a fourth order behavior in circumferential direction. In addition to these laminar measurements, turbulent flows at higher mass flow rates were investigated. [Preview Abstract] |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D27.00007: Evaluation of performance of multi-sensors hot-wire probes using Neural-Networks in-situ calibration Dan Liberzon, Eliezer Kit Neural Networks (NN) based \textit{in-situ} calibration of hot-wire anemometers was recently successfully implemented in field measurements. Although proving feasibility of field measurements using this, relatively new, calibration method the acquired field data also revealed some significant ambiguities in use of combined two- or three-sensor probes. A clearly better behavior of the probe comprised of four sensors (a pair of X shaped probes) has motivated the presented here work, aimed to investigate the NN based procedure performance dependence on the number of wires in the probe. Hypothesizing that the main reason for performance differences is in the fact that a 3-wire probe lacks any special features to withstand the noise in the signal due to temperature fluctuations and sensors' contamination, series of wind tunnel experiments with grid generated turbulence were designed and performed. Performance of a various multi-sensor probes' geometries was examined using the NN based method, while standard calibration data sets were also obtained prior to each set of measurements serving as a reference and as alternative training sets for the NN. The obtained results clearly indicated an advantage in using a symmetrical geometry, and especially using the four-sensor probe to obtain a reasonable description of the 3D velocity field. This is argued to be a result of redundant information on one or several velocity components present in four-sensor probes and serving as an efficient tool for noise reduction. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D27.00008: A novel time-to-space conversion method bypassing the problems with Taylor's hypothesis caused by fluctuating convection velocities Clara Velte, Preben Buchhave A novel conversion of point-measured temporal turbulence power spectra to wavenumber space is proposed. By converting the temporal measurement records into spatial connected streakline elements, the classical assumption of a local mean velocity in Taylor's hypothesis can be completely bypassed. Laser Doppler velocimetry measurements, which in themselves are particularly suitable for application of this technique, taken at different off-center positions in a round turbulent jet are then used to demonstrate the difference between the current and the classical temporal-to-spatial domain conversions. The novel method displays the same behavior as observed from true spatial spectra measured along homogeneous directions in the very same turbulent axisymmetric jet, while the classical Taylor's hypothesis, as expected, shows increasing deviation further away from the center axis where the turbulence intensity grows rapidly. Interpretation of first- and second-order statistics including different kinds of spectral estimates are discussed in a related talk by P Buchhave.\\ 1. Denmark U. of Tech., Kgs. Lyngby, Denmark\\ 2. Intarsia Optics, Birker{\o}d, Denmark\\ [Preview Abstract] |
Sunday, November 22, 2015 3:54PM - 4:07PM |
D27.00009: Turbulence power and kinetic energy spectra measured by a temporal-to-spatial record conversion Preben Buchhave, Clara Velte A method of converting a time record of turbulent velocity measured at a point in a flow to a spatial velocity record consisting of consecutive streak line elements that allows computation of turbulent kinetic wavenumber spectra is briefly introduced (more detail in a related paper at this conference, see ref). The method completely bypasses the problems with Taylor's hypothesis caused by fluctuating convection velocities. In the present contribution, we discuss the interpretation of the first order static moments (e.g. mean and rms velocity) and second order dynamic moments (e.g. spatial correlation function and energy spectrum) computed from the spatial record, which was derived from the measured temporal record. We compare several possible versions of the new energy spectra with the classical 1D and 3D energy spectra and the so-called total kinetic energy spectrum and discuss the range of validity of any equivalence between the new computations and the classical ones. Ref.: Clara M. Velte: A novel time-to-space conversion methods bypassing the problems with Taylor's hypothesis caused by fluctuating convection velocities [Preview Abstract] |
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