Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session LI: Experimental Techniques II |
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Chair: Yiannis Andreopoulos, City University New York Room: Tampa Marriott Waterside Hotel and Marina Meeting Room 5 |
Tuesday, November 21, 2006 8:00AM - 8:13AM |
LI.00001: Simultaneous velocity and temperature measurements in turbulent flows using laser-cantilver anemometry and a thermocouple sensor Michael H\"olling, Florian Heidemann, Marino Beenhakker, Stephan Barth, Achim Kittel, Joachim Peinke We present a setup that combines our newly developed laser-cantilever anemometer (LCA) and temperature sensor. These sensors allow for high temporal and spatial resolution measurements. The LCA measures flow velocity by optically detecting the deflection of a tiny cantilever. A coaxial thermocouple of gold and platinum with a diameter of around 1 micrometer gives information about the temperature. The goal of the work is to measure fluid temperature and velocity in 'one spacial point' by positioning the sensor tips as close to one another as possible. Due to the different measurement principles of both sensors we do not expect any significant interference. In the analysis we focus on correlations between temperature fluctuations and velocity fluctuations, which is of current interest in local isotropic turbulence research. [Preview Abstract] |
Tuesday, November 21, 2006 8:13AM - 8:26AM |
LI.00002: MR Velocimetry Protocols for Small Water-Filled Channels L. Guy Raguin, Dimitrios C. Karampinos, Luisa Ciobanu, John G. Georgiadis Unlike optical velocimetry methods, nuclear magnetic resonance (NMR) relaxes the requirement of having optical access to flow, and additionally allows multiple field-specific contrast mechanisms (fluid displacement, diffusion, chemical species, etc). For small channel networks, the trade-offs between spatial and temporal resolutions leads to the following conundrum: it is better to obtain spatially resolved velocity fields but only for slowly evolving flows, or temporally resolved average velocities in each of the small channels? To explore this issue, we compare a fast and localized NMR velocimetry technique based on multiple modulation multiple echoes (MMMEV), with classical NMR imaging velocimetry protocols (flow-compensated phase-contrast spin-echo, pulse-gradient spin-echo, and spin-tagging spin-echo) in a microchannel network. [Preview Abstract] |
Tuesday, November 21, 2006 8:26AM - 8:39AM |
LI.00003: RELIEF Velocimetry for Large-Scale Wind Tunnel Facilities S. Gogineni, W. Lempert, J. Gord, R. Schmit The U.S. Air Force Research Laboratory (AFRL) has determined that a need exists for a seedless diagnostic instrumentation capable of obtaining quantitative flow data in large scale aerodynamic facilities, with particular emphasis on the high subsonic to moderate supersonic flow regimes. For this purpose, a RELIEF (Raman Excitation + Laser Induced Electronic Fluorescence) technique using ultra-fast laser technology is being developed. During the Phase I program, it was demonstrated that: (i) Raman shifting cells, which offer great system simplicity and increased robustness, can be used to generate the required Stokes tagging beam when using psec pulses, (ii) psec tagging result in efficient vibrational excitation (tagging) and that it enables the use of greatly (factor of ten) reduced single pulse energy, and (iii) the ArF excimer interrogation laser can be replaced with an Nd:YAG-based system. During the Phase II program, focus is being made on optimization of the optical technologies demonstrated in Phase I and delivery and integration of a complete ultra-fast flow tagging system to the AFRL Trisonic Flow Facility. These details along with the implementation of the integrated system to make velocity field measurements of the flow produced external to and within a transonic cavity model will be presented. Authors acknowledge the help of Y. Zuzeek, M. Uddi, K. Frederickson, N. Jiang, S. Roy, and T. R. Meyer for their contributions during the experiments. [Preview Abstract] |
Tuesday, November 21, 2006 8:39AM - 8:52AM |
LI.00004: MEMS Based Flow Sensors and Their Application on Flow Imaging Yingchen Yang, Nannan Chen, Jonathan Engel, Craig Tucker, Saunvit Pandya, Chang Liu We report characterization and application of recently developed, MEMS based, out-of-plane hot-wire anemometer (HWA) sensor and bio-inspired artificial hair cell (AHC) sensor. Sensitivities of 0.2mm/s for HWA and 0.1mm/s for AHC have been achieved in water flows, comparing with 1mm/s of a conventional HWA. In contrast to its high sensitivity, the AHC sensor can survive 55\r{ } bending of its hair, making it very robust. After calibration, both HWA and AHC sensors were employed for dipole field and wake measurements. The dipole field was generated by a vibrating sphere in a large water tank; the measurement results match very well with the analytical model. The wake was created by a circular cylinder in a water channel; the RMS velocity distributions replicate the main features of a typical wake accurately. The two types of sensors were also applied in array format to mimic a fish lateral line for imaging hydrodynamic events. Multi-modal sensors capable of simultaneous measurement of flow velocity, shear stress, pressure and temperature are under development. [Preview Abstract] |
Tuesday, November 21, 2006 8:52AM - 9:05AM |
LI.00005: ABSTRACT WITHDRAWN |
Tuesday, November 21, 2006 9:05AM - 9:18AM |
LI.00006: A New Sensor for Image Based Skin Friction and Pressure Measurements. Jim Crafton, Sergey Fonov, Grant Jones, Larry Goss, Robert Forlines A new material for distributed measurements of pressure and skin friction has been developed. The active element for this sensor is a thin film made of an elastomer with known thickness and shear modulus. The film deforms under load but does not compress or yield. The measurement is accomplished by monitoring the normal and tangential deformations of the film and then converting these deformation fields into pressure and skin friction using a physical model of the film. This technology is currently being utilized in wind tunnels, water tunnels, and biological flows. Several quantitative and qualitative experimental results will be presented including measurements of pressure and skin friction; in sub-sonic and supersonic wind tunnels, shock-boundary layer flow control with a plasma actuator, flow near a strut end-wall junction in a water tunnel, skin friction validation measurements in a fully developed channel flow, skin friction measurements in an artificial heart model (non-Newtonian fluid), and contact force measurements. These experiments demonstrate the ability of this sensor for quantitative measurements in a variety of fluids and flows. [Preview Abstract] |
Tuesday, November 21, 2006 9:18AM - 9:31AM |
LI.00007: Current Control of an A.C. Plasma Anemometer for Hypersonic Flow Measurements Eric Matlis, Thomas Corke, Sivaram Gogineni A miniature 2 MHz a.c. driven, weakly-ionized plasma anemometer for measurements at hypersonic Mach-numbers has been developed. This device uses a glow-discharge between two electrodes as the sensing element. Advantages of the glow discharge to flow measurements are its native high frequency response and robust construction, compared to traditional thermally based hot-wire sensors or mems-type devices. It has a small spatial volume and can provide point measurements in flows that are optically restricted. This device has a low power requirement less than 5 Watts at 350 Vrms with 0.076 mm gap and can be used at atmospheric pressures. It requires no electronic compensation to achieve a frequency response up to its a.c. carrier frequency, produces an amplitude-modulated output that has excellent common-mode rejection with a signal-to-noise ratio better than a hot-wire, and is insensitive to temperature variations making calibration easier than thermal-based sensors. Continued development of the sensor has focused on the choice of geometry and materials of the electrodes to improve reliability and reduce size, as well as the development of a constant-current control scheme. This control method regulates the glow-discharge current in a feed-back loop to respond to changes in mean flow mass-flux. [Preview Abstract] |
Tuesday, November 21, 2006 9:31AM - 9:44AM |
LI.00008: On the accuracy of the velocity and velocity gradient statistics measured with multi-sensor hot-wire probes Petar Vukoslavcevic, Elias Balaras, James Wallace A highly resolved turbulent channel flow DNS with Re$_{\tau }$= 180 has been used to investigate the ability of multi-sensor hot-wire probes to accurately measure velocity and velocity gradient based statistics. Various sensor separations have been tested in order to study the effects of spatial resolution on the measurements. First, the effective cooling velocity has been determined for each sensor for (1) an idealized probe where the influence of the velocity component tangential to the sensors and flow blockage by the presence of the probe are neglected and (2) for a real probe, the characteristics of which have been determined experimentally. By simulating the response of the probes for these two cases to obtain the effective velocities cooling the sensors, velocity and vorticity component statistics have been calculated for two cases. These are (1) neglecting the velocity gradients for a two-sensor probe that can only measure velocity components and (2) assuming these gradients to be constant over a 12-sensor probe sensing area that can measure both velocity and vorticity components. These assumptions are unavoidable for real measurements with these two types of probes. [Preview Abstract] |
Tuesday, November 21, 2006 9:44AM - 9:57AM |
LI.00009: Evaluation of aerodynamic performance of multi hot-wire vorticity probes through CFD analysis Minwei Gong, Savvas Xanthos, Yiannis Andreopoulos The need to measure velocity gradients based quantities like rates of rotation, strain and dissipation of turbulent kinetic energy with good spatial and temporal resolution has led to the development of multi hot-wire probes which often consists of several arrays with 9 or 12 wires which require 18 to 24 prongs in total. Improving spatial resolution in the measurements of turbulence is the major reason for miniaturization of these probes. However, as the size of these probes is reduced, the effect of the size of the prongs and the probe holder becomes critical and it may affect the flow pattern around the probe. The flow around the vorticity probe developed by Agui et al (JFM, \textbf{524}, 143, 2005) and used in our shock tube experiments has been extensively simulated through CFD analysis. The evaluation included tests of velocity magnitude, response to yaw and pitch variation of incoming velocity vector, interaction with forward and backward traveling shock waves and expansion fans. The velocity measured by each of the 12 sensors of the probe is the average velocity over cells along the length of the corresponding wire. The results of yaw and pitch response provided an assessment of the acceptance cone of the probe which was compared to that obtained experimentally. [Preview Abstract] |
Tuesday, November 21, 2006 9:57AM - 10:10AM |
LI.00010: Energy harvesting of wind-driven piezoelectric membranes in the wake of bluff bodies. Todd Novak, Ivan Marusic, William Robbins In recent years a unique method of passive energy harvesting has been developed for off-grid applications. This method utilizes piezoelectric membranes, commonly called piezoelements or bimorphs, placed in a fluid flow. The resulting strain from the periodic undulations of the membrane is converted into a voltage across the surfaces of the membrane via the piezoelectric effect. In our present study we have examined the oscillatory nature of the membrane when placed in the wake of a bluff body in an air flow. Our aim has been to determine the appropriate geometry and spacing given a range of wind speeds such as to achieve optimal power harvesting. We present results from experiments using high-speed digital photography and hotwire anemometry where we analyze the motion of the membrane under varying wind speeds, aspect ratios, and membrane stiffness. [Preview Abstract] |
Tuesday, November 21, 2006 10:10AM - 10:23AM |
LI.00011: Parametric Optimization of Single Dielectric Barrier Discharge (SDBD) Plasma Actuators. Muhammad O. Iqbal, Alexey Kozlov, David Schatzman, Hesham Othman, Flint Thomas, Thomas Corke There has been growing interest in flow control using dielectric barrier discharge plasma actuators in recent years. However, studies regarding optimization of plasma actuators are relatively scarce. Current study is intended to optimize the body force produced by plasma discharge (steady and unsteady) which is a function of various parameters such as dielectric material, size of electrodes, their overlap, frequency, voltage, etc. Detailed experiments are performed in a controlled environment with no-external-flow condition with several different dielectric materials of various thicknesses. Plasma induced velocity (using glass pitot probe), body force (using high precision weighing scale), and power dissipation are measured at various voltages and frequencies. Optimal voltage waveform and frequency has been found which resulted in time averaged maximum induced velocity and body force. This has resulted in an order of magnitude improvement of the actuator effect. The results obtained follow a relatively simple mathematical model that allows one to derive analytical expressions for electrical characteristics of plasma actuators. [Preview Abstract] |
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