Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session QW: Experimental Techniques III |
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Chair: Peter Monkewitz, Ecole Polytechnique Federale de Lausanne, Switzerland Room: Hyatt Regency Long Beach Regency C |
Tuesday, November 23, 2010 12:50PM - 1:03PM |
QW.00001: Spatial filtering and end-conduction effects in turbulence measurements using hot wires Anand Ashok, Marcus Hultmark, Alexander Smits We use grid generated homogeneous isotropic turbulence as a benchmark flow to test the effects of spatial resolution on turbulence measurements with hot wires. The grid turbulence is generated in a low speed 2' by 3' closed circuit wind tunnel using a 0.25'' square mesh grid placed at the test section inlet. Measurements of the turbulence statistics and spectra downstream of the grid were made using hot-wires with a constant diameter but varying lengths. An empirical correlation for the attenuation of the energy due to spatial filtering is constructed as a function of the parameter l/$\eta $. In addition, we show that end conduction effects depend not only on the l/d ratio but also on the wire material and the wire Reynolds number. [Preview Abstract] |
Tuesday, November 23, 2010 1:03PM - 1:16PM |
QW.00002: On the optimal number and sensor arrangement of multi-sensor hot-wire probes to measure the velocity vector and the velocity gradient tensor in turbulent boundary layers P. Vukoslavcevic, J. Wallace, N. Baratlis, E. Balaras Although a 3-sensor array should be sufficient to simultaneously measure the three velocity components, and three such arrays can be combined to measure the six velocity gradients in the cross-stream plane, a fourth sensor has been used for probes developed over the last two decades in order to increase measurement accuracy and the uniqueness range of multi-sensor hot-wire probes. A highly resolved turbulent channel flow DNS with $Re_\tau = 200$ was used to investigate the optimal sensor number and arrangement. The sensors were represented as points on the simulation grid, the effective velocity cooling each sensor was determined assuming an ideal sensor response, and the sensor equations were then solved in response to the DNS field to obtain velocity vector and velocity gradient tensor components. It will be shown that the fourth sensor of each of the three arrays is unnecessary for turbulent boundary layer flow measurements if the arrays' three sensors are arranged judiciously. Requiring only nine sensors instead of twelve is a great advantage with respect to probe construction, size and sensor interference. Results from the types of 12-sensor probes previously used will be compared to those from an optimally designed 9-sensor probe. [Preview Abstract] |
Tuesday, November 23, 2010 1:16PM - 1:29PM |
QW.00003: Two-dimensional Laser-Cantilever-Anemometer with re-designed cantilever chip - measurements and characterization Michael Hoelling, Jaroslaw Puczylowski, Joachim Peinke We present measurements performed with the two-dimensional Laser-Cantilever-Anemometer (2D-LCA) equipped with a re-designed cantilever chip. The 2D-LCA measures flow velocities by detecting the deflection of a tiny cantilever (about 140 x 40 micrometer) brought into the flow by means of the laser pointer principle. Latest investigations show a combination of both twisting and bending behavior of the cantilever for inclined angles of attack. Measurements for different combinations of angles of attack and velocities result in an unambiguous two-dimensional calibration which allows the 2D-LCA for simultaneous measurements of these two quantities, and of the longitudinal and transversal velocity component respectively. The new cantilever chip has a vertical structure added at the tip of the cantilever in order to increase the sensitivity to flows from angles of attack different than zero degrees. We present measurements taken with the new cantilever chip in turbulent laboratory flows in comparison to the old cantilever design and to x-wire anemometry data. [Preview Abstract] |
Tuesday, November 23, 2010 1:29PM - 1:42PM |
QW.00004: Infrared quantum dots as liquid temperature tracers for imaging through silicon Myeongsub Kim, Minami Yoda Although a number of optical thermometry techniques estimate fluid temperature fields from changes in the lifetime or intensity of the emissions from fluorescent or phosphorescent species, the majority of these techniques rely on imaging optical signals at visible wavelengths. Silicon (Si), commonly used in microelectronics and microelectromechanical systems (MEMS), is however opaque at these wavelengths, and only becomes partially transparent at near-infrared (IR) wavelengths above $\sim $1.2~$\mu $m. Given the lack of fluorescent species with emissions in the near-IR, colloidal nanocrystals, or ``quantum dots'' (QD), of lead sulfide overcoated with cadmium sulfide using a new process with a diameter of 5.7~nm were investigated as temperature tracers. The emissions around 1.35~$\mu $m from these PbS/CdS QD suspended in toluene at an absorbance of 0.45 were found to decrease by about 0.5{\%} per \r{ }C increase in the suspension temperature $T$ for $T$~=~20-60~\r{ }C with a standard deviation that gave an uncertainty in $T$ of $\sim $0.3~\r{ }C. The overcoating greatly improves the stability of the QD, and the temperature response of these tracers was consistent for suspended samples stored up to 103 days under nitrogen as well as up to 1 day under air. [Preview Abstract] |
Tuesday, November 23, 2010 1:42PM - 1:55PM |
QW.00005: Temperature characterization of CdSe/ZnS quantum-dots applied on anodized-aluminum coating Akihisa Aikawa, Hirotaka Sakaue We have developed a quantum-dot (QD) based anodized-aluminum temperature-sensitive paint (AA-TSP) as a global temperature sensor. Compared to a conventional TSP, which uses a polymer as a supporting matrix, the AA-TSP can provide a narrow FWHM that provides a potential to create a multi-color TSP. By using anodized aluminum as a supporting matrix, the resultant AA-TSP extends the temperature detection range, which is limited by a conventional supporting matrix of a polymer. The temperature calibration shows that a resultant AA-TSP can detect the temperature from 100 to 500 K. Six different QDs are chosen for temperature characterizations of the AA-TSP, whose luminescent peaks are at 481, 518, 543, 555, 587, and 615 nm in toluene. The temperature sensitivity of the resultant AA-TSP ranges from -0.6 to -1.5 percent/K. With increase in the luminescent peak, the sensitivity increases. An application of the resultant AA-TSP for a global temperature measurement in a hypersonic wind tunnel is included in addition to the temperature characterizations. [Preview Abstract] |
Tuesday, November 23, 2010 1:55PM - 2:08PM |
QW.00006: Fluorescence thermometry measurements of wall surface and bulk fluid temperatures Myeongsub Kim, Minami Yoda Measuring fluid temperature fields at micron-scale spatial resolution is of interest in applications including microelectronic cooling and microfluidics. Fluorescence thermometry (FT), where temperatures are estimated from variations in the emission intensity of various fluorophores, is commonly used to measure liquid temperatures in a variety of flows. Here dual-tracer FT (DFT) where fluorescein (Fl) and sulforhodamine B were volumetrically illuminated was used to measure temperature fields in the Poiseuille flow of water through a heated 1 mm square channel. The average experimental uncertainties in the DFT results are estimated to be $<$0.3~\r{ }C at a spatial resolution of 30~$\mu $m in the image plane at \textit{Re }= 3.3 and 8.3. Evanescent-wave FT (EFT) where only Fl is illuminated by evanescent waves was also used to measure the liquid-phase temperature field within the first 0.3~$\mu $m next to the wall with an average uncertainty of $<$0.2~\r{ }C at a resolution of 10 $\mu $m. Comparison with numerical predictions show that the EFT results are effectively the wall surface temperature. Comparison of the DFT data with numerical predictions suggest that the spatial resolution of these data along the optical axis is at least an order of magnitude greater than the depth of field. [Preview Abstract] |
Tuesday, November 23, 2010 2:08PM - 2:21PM |
QW.00007: Response time characterization of fast responding pressure-sensitive paint Tatsuya Ozaki, Hitoshi Ishikawa, Hirotaka Sakaue Response time characterization of a fast responding pressure-sensitive paint (PSP) is important information in measuring an unsteady flow field. PSP is an optical pressure sensor. The luminescent image from the PSP is related to a pressure map. In the previous works, a time delay from a step change of pressure is generally used to characterize the response time. The thickness of the PSP as well as the PSP binding material greatly influences the response time. Because the temperature influences the diffusion or permeation of a PSP binder, it is also an important parameter to influence the response time. We build a shock tube to create a step change of pressure for response time characterization. This can control the temperature of the PSP. We discuss the PSP response times related to the temperature of the binder as well as the binding materials. [Preview Abstract] |
Tuesday, November 23, 2010 2:21PM - 2:34PM |
QW.00008: Motion-cancelled PSP system for obtaining global unsteady fields of a moving object Kensueke Miyamoto, Takeshi Miyazaki, Hirotaka Sakaue A motion-cancelled PSP system is introduced for obtaining global unsteady fields on a moving object. This system uses a reference- and signal-image simultaneously acquired by a digital camera. Each image is provided by a two-color pressure-sensitive paint (PSP). The luminescent outputs from the PSP are converted to the pressures or the oxygen concentrations. The existing system uses a color CMOS camera. The green and red images of the camera correspond to the reference and signal images, respectively. Due to the spectral overlay of the images, the pressure sensitivity of the existing system is poor (0.13 percent/kPa). To improve the sensitivity, a spectral separation is necessary. As an improved system, we use a two-CCD chip camera, which can select the band-pass filters in front of the chips. The filters can limit the wavelength range of each luminescent image that prevents the spectral overlay. A comparison with the existing system is provided, and the developed system is applied to an oscillating unsteady motion of a flat plate for demonstration. [Preview Abstract] |
Tuesday, November 23, 2010 2:34PM - 2:47PM |
QW.00009: A Study of Surface-Pressure Estimation from Multiline Molecular Tagging Velocimetry Data Ahmed Naguib, Manoochehr Koochesfahani This study is motivated by the extraction of surface-pressure information from Molecular Tagging Velocimetry (MTV) data in order to correlate unsteady flow structures with surface forces. The approach we take is to integrate the pressure-gradient acting on the wall, which for a stationary surface can be computed from knowledge of the wall vorticity flux. The latter requires calculation of the second derivative of the velocity at the wall, which is generally difficult to estimate accurately from near-wall velocity data. In this work, we seek to address this issue by capitalizing on the unique ability of MTV to provide very fine resolution of single-velocity-component data near the wall. The accuracy of determining the wall vorticity flux (and surface pressure) from such measurements is examined using theoretical solutions of simple flows and numerical databases. The results provide a guide for the selection of the measurement parameters for accurate implementation of the method, as well as shed light on the practical limits of its applicability. [Preview Abstract] |
Tuesday, November 23, 2010 2:47PM - 3:00PM |
QW.00010: An Assessment of Oil Film Interferometry to Measure Skin Friction Peter A. Monkewitz, Antonio Segalini, Jean-Daniel R\"uedi In recent years, the independent measurement of wall shear stress with oil film interferometry has led to a step increase in the understanding of turbulent boundary layers. However, while many arguments depend critically on a precise knowledge of the skin friction, the systematic errors of the oil film technique are not well known. In particular the basic theory underlying the technique has essentially not evolved since it was first proposed by Tanner \& Blows (J. Phys. E: Sci. Instrum., vol. 9, 1976, p. 194). The purpose of this study is to elucidate the dominant systematic error of the classical oil film method. We derive the corrections to the basic Tanner \& Blows similarity solution for the film development in zero pressure gradient boundary layers and validate the analysis experimentally. This allows to formulate ``best practice guidelines'' for the oil film technique that help push uncertainties below 1\%. [Preview Abstract] |
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