Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session H31: Experimental Techniques - Laser/Wire Anemometry |
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Chair: Laurent Mydlarski, McGill University Room: F152 |
Monday, November 21, 2016 10:40AM - 10:53AM |
H31.00001: High resolved velocity measurements using Laser Cantilever Anemometry Jaroslaw Puczylowski, Michael Hölling, Joachim Peinke We have developed a new anemometer, namely the 2d-LCA (2d-Laser-Cantilever-Anemometer), that is capable of performing high resolved velocity measurements in fluids. The anemometer uses a micostructured cantilever made of silicon as a sensing element. The specific shape and the small dimensions (about 150\textmu m) of the cantilever allow for precise measurements of two velocity component at a temporal resolution of about 150kHz. The angular acceptance range is 180\textdegree in total. The 2d-LCA is a simple to use alternative to x-wires and can be used in many areas of operation including measurements in liquids or in particle-laden flows. Unlike hot-wires, the resolution power of the 2d-LCA does not decrease with increasing flow velocity, making it particularly suitable for measurements in high-speed flows. In the recent past new cantilever designs were implemented with the goal to further improve the angular resolution and increase the stability. In addition, we have designed more robust cantilevers for measurements in rough environments such as offshore areas. Successful comparative measurements with hot-wires have been carried out in order to assess the performance of the 2d-LCA. [Preview Abstract] |
Monday, November 21, 2016 10:53AM - 11:06AM |
H31.00002: A nano cold-wire for velocity measurements Yi-Chun Huang, Matthew Fu, Yuyang Fan, Clayton Byers, Marcus Hultmark We introduce a novel, strain-based sensor for both gaseous and liquid flows. The sensor consists of a free-standing, electrically conductive, nanoscale ribbon suspended between silicon supports. Due to its size, the nanoribbon deflects in flow under viscously dominated fluid forcing, which induces axial strain and a resistance change in the sensing element. The change in resistance can then be measured by a Wheatstone bridge, resulting in straightforward design and operation of the sensor. Since its operating principle is based on viscous fluid forcing, the sensor has high sensitivity especially in liquid or other highly viscous flows. A simple analytical model to understand the relation between forcing and strain is derived from the geometric and material constraints, and preliminary analysis using a low order model of the dynamic systems suggests that the sensor has a high frequency response. Lastly, a cylindrical structure to house the sensor with an axial and ventral channel to generate a pressure differential is being considered for typical velocimetry applications. [Preview Abstract] |
Monday, November 21, 2016 11:06AM - 11:19AM |
H31.00003: ABSTRACT WITHDRAWN |
Monday, November 21, 2016 11:19AM - 11:32AM |
H31.00004: Investigation of Constant Temperature Hot-wire System Response using Laser Pulse Nicholas Jaffa, Scott Morris, Joshua Cameron Constant temperature hot-wire systems use a Wheatstone bridge and feedback amplifier circuit to maintain a constant average temperature across the wire yielding frequency responses of order 100 kHz. This high frequency response allows hot-wires to be used extensively for aerodynamic measurements in high speed flows and uncertainty at these high frequencies can be difficult to diagnose. The standard frequency response check for constant temperature hot-wires uses an electronic pulse across the circuit to check the electronic feedback circuit response time, but does not account for the impact of the heat transfer along the wire. In order to investigate the frequency response of the entire constant temperature hot-wire system, including the heat transfer along the wire, a novel method was developed using a pulsed PIV laser focused to illuminate only the hot-wire. The laser pulse duration was effectively an instantaneous change in wire surface temperature through radiation. A hot-wire was placed in a uniform open calibration jet for a range of flow conditions. The response of the entire hot-wire system was observed across a range of conditions including changes in flow, wire temperature, and thermal boundary conditions and compared with the electronic pulse test. [Preview Abstract] |
Monday, November 21, 2016 11:32AM - 11:45AM |
H31.00005: Validation of a multi-sensor hotwire probe for boundary layer enstrophy measurements Spencer Zimmerman, Caleb Morrill-Winter, Joseph Klewicki A multi-sensor hotwire probe capable of measuring the velocity and vorticity vectors has been designed and implemented in a turbulent boundary layer with the goal of educing the means by which the associated momentum transport is maintained under increasing scale separation between the velocity and vorticity fields with increasing Reynolds number. The capacity of this sensor to accurately measure each component of velocity and vorticity is first evaluated via synthetic experiment. The three-dimensional velocity field from the DNS of Sillero et al. (\textit{Phys. Fluids} \textbf{25}, 2013) is used to compute effective cooling for each sensor element, and the resulting signals are interpreted via two-dimensional calibration surfaces such as would be used to process physical experimental data. Results from this virtual validation experiment are presented and suggest the sensor is capable of resolving key features of the velocity and vorticity fields at physically achievable spatial resolutions. Results from measurements collected at the Flow Physics Facility (FPF) at the University of New Hampshire are presented alongside these projections and exhibit very good agreement in trend, but with some differences in magnitude. [Preview Abstract] |
Monday, November 21, 2016 11:45AM - 11:58AM |
H31.00006: Novel method and experimental validation of statistical calibration via Gaussianization in hot-wire anemometry Igal Gluzman, Jacob Cohen, Yaakov Oshman We introduce a statistical method based on Gaussianization to estimate the nonlinear calibration curve of a hot-wire probe, that relates the input flow velocity to the output (measured) voltage. The method uses as input a measured sequence of voltage samples, corresponding to different unknown flow velocities in the desired operational range, and only two measured voltages along with their known (calibrated) flow velocities. The novel method is validated against standard calibration methods using data acquired by hot-wire probes using wind-tunnel experiments. We demonstrate our new calibration technique by placing the hot-wire probe at certain region downstream of a cube-shaped body in a free stream of air flow. For testing our calibration method we rely on flow statistics that exist, among others, in a certain region of a turbulent wake formed downstream of the cube-shaped body. The specific properties are: first, the velocity signal in the wake should be as close to Gaussian as possible. Second, the signal should cover the desired velocity range that should be calibrated. The appropriate region to place our probe is determined via computation of the first four statistical moments of the measured signals in different regions of the wake. [Preview Abstract] |
Monday, November 21, 2016 11:58AM - 12:11PM |
H31.00007: Recommendations for the design of interference probes for the simultaneous measurement of turbulent concentration and velocity Ala\''{i}s Hewes, Laurent Mydlarski The present work focuses on the design and optimization of a thermal-anemometry-based interference probe used to simultaneously measure concentration and velocity at relatively high temporal and spatial resolutions in turbulent flows. Although a small number of similar measurements have been successfully performed, little work has been undertaken to investigate the design of such specialized probes, in which one hot-wire sensor is operated downstream of, and micrometers from, a second one. To this end, experiments performed in the non-buoyant region of a helium-air jet were undertaken to study the effects of overheat ratios, wire separation distances, wire diameters, and wire materials on the performance of interference probes. They revealed that accurate concentration and velocity measurements require that an interference probe have two wires of differing diameters with a small separation, of about 10 $\mu$m, between the wires. Furthermore, the upstream wire should be operated at a high overheat ratio and the downstream wire at a low one. An optimal design for an interference probe is presented, and measurements made in a turbulent jet are used to benchmark its accuracy. [Preview Abstract] |
Monday, November 21, 2016 12:11PM - 12:24PM |
H31.00008: Practical Considerations for Simultaneous LDV {\&} PIV~Measurements~ Stamatios Pothos, Aaron Boomsma, Dan Troolin Simultaneous LDV and PIV measurements are useful for validation experiments and~when correlating high temporal resolution measurements~with large~structures of the flow. ~~Performing simultaneous LDV and PIV measurements can be a challenging task due to the differences in temporal and spatial resolution of each technique, as well as requirements for adequate signal. Even so, simultaneous hot-wire and PIV measurements is even more difficult. ~Unlike~hot-wire, LDV~is a non-intrusive~technique that is unaffected by PIV laser light-sheet heating. Furthermore, hot-wire measurements are adversely affected by seeding particles in the flow required for PIV. ~In the present study, we discuss several practical considerations for performing simultaneous LDV and PIV measurements. ~We completed two separate experiments, each with~different seeding densities, flow velocities,~and working fluids. ~With these data sets, we~studied~the effects of temporal and spatial interpolation, up/down sampling, PIV window size and overlap on the simultaneous signals.~ [Preview Abstract] |
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