Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session L14: Experimental Techniques VI: Turbulence/Fluorescence |
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Chair: David Dowling, University of Michigan Room: 302 |
Monday, November 25, 2013 3:35PM - 3:48PM |
L14.00001: A non-intrusive velocity measurement technique for naturally-occurring turbulent shear flows Chin Hei Ng, Ryan Keedy, Alberto Aliseda Turbulent shear flows are common in nature (atmospheric low level jets, ocean hydrothermal vents, volcanic eruptions, convective cells, etc) and play an important role in environmental processes. These frequently inaccessible and measurements that require a physical probe are both restricted and inaccurate. We propose a non-intrusive technique that estimates the velocity of these flows by taking advantage of the existence of natural markers, such as condensation droplets, gas bubbles, reflective turbulent features on the mixing interface, that can be observed in video of the phenomena. Displacement of these markers, assumed to behave as fluid material elements, is measured by digital image correlation, and that velocity is associated with the fluid superlayer at the mixing interface between the ``seeded'' and unseeded flows. The relationship between these superficial velocities and the velocity in the interior of the flow has been investigated in a turbulent round jet laboratory experiment that allows for variations in jet Reynolds number, jet density, and jet viscosity. Influence of imaging parameters was also studied, with particular relevance to the application of this technique to the field. [Preview Abstract] |
Monday, November 25, 2013 3:48PM - 4:01PM |
L14.00002: PIV Measurements of Turbulent Flow Over a Permeable Wall using a Refractive-Index Matching Approach T. Kim, G. Blois, J.L. Best, K.T. Christensen Turbulent flows over permeable walls occur in a variety of natural environments and engineering applications. Unlike classical and widely-studied flows over impermeable walls, the peculiar dynamics of flow generated by permeable walls are poorly understood. Early studies suggest that the well-known higher energy dissipation induced by permeability (as compared to impermeable walls with similar roughness) can be explained by unveiling the flow interactions within the transition layer that forms at the interface between the overlying flow and the permeable wall. To overcome the challenges associated with quantifying the flow character both above and within a permeable wall, a Refractive-Index-Matching (RIM) approach was employed. Doing so facilitated optical access to the fluid flowing through the permeable wall, thus yielding direct PIV pore-space flow measurements within the transition layer. The permeable wall was formed by packing acrylic spheres in a cubic arrangement and was then immersed in an aqueous solution of sodium iodide at a concentration and temperature that ensured accurate refractive index match with the wall. Measurements were focused on the flow across the wall interface and the turbulent attributes of these surface--subsurface interactions were detailed. [Preview Abstract] |
Monday, November 25, 2013 4:01PM - 4:14PM |
L14.00003: Simultaneous Velocity and Vorticity Measurement in Turbulence Huixuan Wu, Haitao Xu, Eberhard Bodenschatz A new paradigm of simultaneous velocity and vorticity measurement is developed to study turbulence. Instead of deducing vorticity from velocities measured at neighboring points, this innovative approach detects the translations and rotations of micro-sized particles directly. These hydrogel particles are spherical, transparent, and encapsulate micro-mirrors. This method outstands conventional ones, e.g., hotwire arrays or PIV because its spatial resolution is much higher. It does not require a non-zero mean flow, and it can provide all three vorticity components, which is not available from planar PIV data. Its principle is to illuminate the mirror and utilize the variation of the reflection directions to deduce the local flow vorticity. Meanwhile, the particle position is recorded as in normal particle tracking. Therefore, the velocity and vorticity of a particle can be obtained simultaneously in Lagrangian framework. The authors have made benchmark experiments to evaluate this novel method in Taylor Couette flows. The results show that the instantaneous vorticity measurement is as accurate as 3{\%}. We are now setting up a von Karman disk pair device to study the turbulent flow. This novel technique will provide unprecedented information of high Reynolds number turbulence [Preview Abstract] |
Monday, November 25, 2013 4:14PM - 4:27PM |
L14.00004: Measurement of turbulent wall shear stress in air using micro-pillars Ebenezer Gnanamanickam, Kevin Kevin, Jason Monty, Nicholas Hutchins The measurement of unsteady wall shear stress in a turbulent boundary layer, especially when the working medium is air, has been a historically challenging problem in experimental fluid mechanics. Recently the micro-pillar shear stress sensor (MPS3) has shown promise in this regard. The MPS3 is an array of micro-pillar mounted on the wall of a model. These micro-pillars deflect an amount proportional to the drag force it experiences. This drag force is proportional to the wall shear stress. The micro-pillar tip deflection is thus tracked using high-speed imaging to yield the unsteady wall shear stress. Here, the MPS3 is used to carry out unsteady wall shear stress measurements in a fully developed channel flow. Both static and dynamic calibrations of the sensor are presented. The wall shear stress statistics obtained in the fully developed channel flow are compared with those obtained from Direct Numerical Simulations (DNS) to provide an assessment of the sensor capabilities. Exemplary measurements such as two-dimensional temporal distribution of the wall shear stress are presented to highlight the capabilities of the sensor. [Preview Abstract] |
Monday, November 25, 2013 4:27PM - 4:40PM |
L14.00005: Measurements of laboratory turbulence with the 2d-Laser Cantilever Anemometer Jaroslaw Puczylowski, Joachim Peinke, MIchael Hoelling A newly developed anemometer, the 2d-Laser Cantilever Anemometer, was used to measure the two-dimensional wind speed vector in laboratory-generated turbulence. The anemometer provides a temporal and spatial resolution comparable or even higher to those of commercial hot-wires and thus is an excellent alternative for high-resolution measurements. The 2d-Laser Cantilever Anemometer uses a previously unseen measurement technique in the range of anemometers. The principle is adopted from atomic force microscopes (AFM). A tiny micro-structured cantilever is brought into the airflow, where it experiences a drag force due to the moving fluid. The resulting deflection is measured using the laser pointer principle. Unlike the measuring principle of hot-wires this technique can be applied in challenging environments such as in liquids or very close to walls. Our comparing measurements with the 2d-Laser Cantilever Anemometer and an x-wire were carried out in the wake of rigid bodies and grids. The results show a great agreement with regards to the increment statistics on various scales, power spectra and turbulence intensity, thus proving the new anemometer. [Preview Abstract] |
Monday, November 25, 2013 4:40PM - 4:53PM |
L14.00006: Development of Krypton Planar Laser-Induced Fluorescence for Supersonic Flow Environments Ross Burns, Chris Combs, Noel Clemens Experimental work is presented on the development of krypton planar laser-induced fluorescence as a tracer in supersonic flows. Fluorescent tracers commonly used in compressible flowfields, such as nitric oxide, acetone, and toluene, have notable disadvantages when used in specific flow conditions that can include tracer condensation, reactivity, and general toxicity. Krypton, a noble gas, is immune to these deleterious effects over a much broader range of conditions including combustion environments. For these studies, the 5p[3/2]$_{\mathrm{2}} \quad \leftarrow $4p$^{\mathrm{6}}$ $^{\mathrm{1}}$S$_{\mathrm{0}}$ electronic transition of krypton, accessible via two-photon absorption, is excited using a tunable sum-frequency generation (SFG) system set at the peak of the atomic absorption line around 214.7 nm. Data is presented on the fluorescence lifetimes and collisional quenching cross-sections over a broad range of conditions for krypton-air mixtures. The technique is demonstrated in a Mach 3 hypermixing flowfield to showcase its utility in a complex compressible and turbulent flow environment. [Preview Abstract] |
Monday, November 25, 2013 4:53PM - 5:06PM |
L14.00007: Non-contacting Measurement of Oil Film Thickness Between Loaded Metallic Gear Teeth Daniel B. Cox, Steven L. Ceccio, David R. Dowling The mechanical power transmission efficiency of gears is depends on the lubrication condition between gear teeth. While the lubrication levels can be generally predicted, an effective in-situ non-contacting measurement of oil film thicknesses between loaded metallic gear teeth has proved elusive. This study explores a novel oil film thickness measurement technique based on optical fluence, the light energy transmitted between loaded gear teeth. A gear testing apparatus that allowed independent control of gear rotation rate, load torque, and oil flow was designed and built. Film thickness measurements made with 5-inch-pitch-diameter 60-tooth spur gears ranged from 0.3 to 10.2 mil. These results are compared with film thickness measurements made in an earlier investigation (MacConochie and Cameron, 1960), as well as with predictions from two film thickness models: a simple two-dimensional squeezed oil film and the industry-accepted model as described by the American Gear Manufacturers Association (AGMA 925, 2003). In each case, the measured film thicknesses were larger than the predicted thicknesses, though these discrepancies might be attributed to the specifics the experiments and to challenges associated with calibrating the fluence measurements. [Sponsored by General Electric] [Preview Abstract] |
Monday, November 25, 2013 5:06PM - 5:19PM |
L14.00008: Plasma Electron Density Measurements Using Phase-Sensitive FTIR Interferometry Brian Neiswander, Eric Matlis, Thomas Corke This work investigates the use of low-temperature plasma as an adaptive medium for high-bandwidth aero-optic wavefront control. To better understand plasma's optical properties (refractive index), a new diagnostic technique has been developed to simultaneously measure the average plasma electron density and heavy particle density. The technique uses phase-sensitive Fourier transform infrared (FTIR) interferometry to measure the optical dispersion of plasma across a spectrum of far-infrared wavelengths. The plasma electron density and heavy particle density values are determined using a least-squares analysis. This presentation describes the experimental setup and preliminary data from the measurement system. [Preview Abstract] |
Monday, November 25, 2013 5:19PM - 5:32PM |
L14.00009: Simultaneous measurement of flow over and transmigration through a cultured endothelial cell layer Lori Lambert, Iraklis Pipinos, Timothy Baxter, Jason MacTaggart, George Karniadakis, Derek Moormeier, Kenneth Bayles, Timothy Wei This talk focuses on the methodologies associated with the integration of temporally and spatially resolved $\mu$PIV measurements of flow over live endothelial cells with measurements of chemical transport through and across the cells. The ultimate goal of the study is to examine and model the transport and transmigration of key agents responsible for the formation of atherosclerotic plaques. Flow over endothelial cells cultured in a microchannel was measured using $\mu$PIV. By making measurements in a number of planes parallel to the wall, key dynamic quantities such as shear and pressure distributions, along with surface topography could be computed from the flow measurements. Experiments were conducted in a 65 $\mu$m x 65 $\mu$m cross section microchannel at shear rates up to 20 dynes/cm$^{2}$. Changes in cell conformation as a function of time after flow was started were examined. The deposition and transmigration of LDL was also examined using fluorescent-tagged LDL molecules. [Preview Abstract] |
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