Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session AA: Turbulent Boundary Layers: Experiments I |
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Chair: Ivan Marusic, University of Melbourne Room: 101A |
Sunday, November 22, 2009 8:00AM - 8:13AM |
AA.00001: ICET - International Collaboration on Experiments in Turbulence: Coordinated Measurements in High Reynolds Number Turbulent Boundary Layers from Three Wind Tunnels H. Nagib, A. Smits, I. Marusic, P.H. Alfredsson Zero pressure gradient (ZPG) boundary layers are one of the canonical, wall-bounded, turbulent flows that have been the focus of experimental and analytical investigations for several decades. Over the past few years, four groups have focused on systematic comparison between several measurement techniques and three facilities. Two closed return wind tunnels with ZPG boundary layers developed on a plate suspended near the mid-height of the test section (at KTH and IIT), and an open return facility with a large and long test section and a boundary layer developing along its floor (at the University of Melbourne), are used for these coordinated efforts. The development length of the boundary layers and the free-stream velocity in the three facilities range from 5.5 to 22 m, and from 10 to 60 m/s, respectively. Various arrangements for adjustable test section ceilings are employed to generate ZPG boundary layers over the range of momentum thickness Reynolds numbers from 11,000 to 70,000. Oil film interferometry (OFI) is employed to directly measure the wall shear stress, and various sizes of Pitot probes and types of hot-wire sensors are used to measure wall-normal velocity profiles at different locations and free-stream velocities. Mean velocity, turbulence statistics and integral parameters are examined. [Preview Abstract] |
Sunday, November 22, 2009 8:13AM - 8:26AM |
AA.00002: Accurate and Independent Measurements of Wall-Shear Stress in Turbulent Flows J.-D. R\"uedi, R. Duncan, S. Imayama, K. Chauhan Oil Film Interferometry (OFI) is used to directly measure the wall-shear stress in the high Reynolds number turbulent boundary layers from three facilities used for ICET. Various optical arrangements were utilized to collect the digital images generated on transparent plugs integrated into the boundary layer surface. Test-section free stream velocities ranging from 10 to 60 m/s and development lengths from 5.5m to 21 m, resulted in friction velocities varying from 0.35 to 1.65 m/s, corresponding to boundary layer thicknesses varying by factors of nearly four. Silicon oils with viscosities from 20 to 1000 cSt were employed in the measurements, with multiple oils used for several of the test conditions. A reference temperature measurement was used in all three facilities and for the calibration of the oils as a function of temperature in four different laboratories using two types of viscometers. The processing of the images was carried out using several approaches and compared for consistency of the results. Results of the skin friction coefficient from the three wind tunnels are examined and compared as a function of the displacement thickness Reynolds number, as determined from hot-wire and Pitot probe profiles at comparable conditions, and are found to be accurately represented by the logarithmic Rotta relation. The various uncertainties and the final accuracy of this type of measurement are discussed. [Preview Abstract] |
Sunday, November 22, 2009 8:26AM - 8:39AM |
AA.00003: Pitot probe corrections for measurements in turbulent boundary layers Jason Monty, Sean Bailey, Marcus Hultmark, Beverley McKeon Mean velocity measurements over a range of Reynolds number have been taken in zero-pressure-gradient, flat plate turbulent boundary layers using Pitot probes of varied diameter. Three world-class boundary layer facilities were involved in this investigation, ensuring the results are not facility-dependent. Different methods of correcting Pitot probe data were compared to each other and to a concurrent study where hot-wire measurements provided mean velocity data. It was found that there was very little difference in the commonly used shear corrections, although improvements could be made in the near-wall corrections and a modification to the correction is proposed. The applicability of a turbulence correction is investigated with the final, fully corrected pitot probe measurements compared with hot-wire measurements, demonstrating excellent agreement overall between the two. This study confirms the accuracy of pitot probes for mean flow analysis in turbulent shear flows. [Preview Abstract] |
Sunday, November 22, 2009 8:39AM - 8:52AM |
AA.00004: Challenges in Hot Wire Measurements in Wall-Bounded Turbulent Flows R. Oerlue, N. Hutchins, T. Kurian, A. Talamelli Despite the rapid development of optical velocimetry methods (like LDV, PIV, etc.) the hot-wire anemometer remains the main instrument used in wind tunnel studies of turbulence. To obtain precise results close to walls in turbulent boundary layers, requires the user to have accurate procedures for a good calibration at low velocities, knowledge of effects of blockage and heat conduction to the wall, and how spatial resolution influences the results. We have carried out measurements in three different wind tunnels (at KTH, Univ. Melbourne and IIT) with various hot-wire probes (stubbed and stubless, as well as straight and boundary layer type) operated with commercially available and home-made anemometer systems. The use of different facilities enabled measurements at similar Reynolds numbers, but with different free stream velocities, resulting in a wide range of viscous scales for the hot-wire sensor lengths. The results indicate that poor spatial resolution influences the measured fluctuating velocity distribution well into the overlap region and clarifies controversial aspects regarding the scaling of the near-wall peak and the apparent existence of an outer peak in the rms distribution. The mean velocity within the buffer region has been found to be affected by probe geometry and size, an influence that is especially important when correcting for the absolute wall position by means of common correction methods. [Preview Abstract] |
Sunday, November 22, 2009 8:52AM - 9:05AM |
AA.00005: Mean Flow Measurements with Pitot Probes in High Reynolds Number Boundary Layers S. Bailey, M. Hultmark, R. Duncan, B. Mckeon Mean velocity profiles were measured in zero-pressure-gradient turbulent boundary layers using a variety of Pitot probes in three facilities at five different Reynolds numbers. The results were analyzed to verify the Reynolds number similarity between the two facilities and the scaling of the integral parameters was found to be consistent with the results from other studies. A linear relationship was found between $Re_{\theta}$ and $Re_{\tau}$ and used to determine a new friction factor relationship based on momentum thickness. Different methods used to determine the von K\'{a}rm\'{a}n constant were compared. When the friction velocity was determined using the new relationship, a logarithmic region between $y^+=300$ and $y/\delta=0.1$ was observed for $Re_{\theta}>15000$. A von K\'{a}rm\'{a}n constant of 0.40 was found for this region. [Preview Abstract] |
Sunday, November 22, 2009 9:05AM - 9:18AM |
AA.00006: Mean Flow Measurements with Hot Wires in High Reynolds Number Boundary Layers R. Duncan, N. Hutchins, A. Segalini, J. Monty Mean flow measurements of high Reynolds number, Zero Pressure Gradient (ZPG) turbulent boundary layers are presented from the ICET data set using hot wire anemometry. The measurements were performed at momentum thickness Reynolds numbers in the range from 11,000 to 70,000, and compared to Pitot probe measurements at the same conditions. Various wire diameters, sensing lengths, probe designs and construction techniques are used, as well as different anemometer setups, in each of the facilities. Mean flow similarity between the three facilities is shown to be well within expected experimental uncertainty and ZPG layer manifestations, both when examining mean velocity profiles and integral parameters. The results reinforce the need for accurate near wall velocity and position measurements, as well as consistent analysis of physical and instrumentation biases. Various approaches are used to determine parameters such as the shape factor, the logarithmic overlap-region parameters, and the wake or outer flow parameters. Parameters extracted from the hot-wire profiles and those based on Pitot probe data are also compared and discussed in light of past experience with both instruments in different wall bounded flow experiments. Finally, consistency of the results is examined between the profile data and the skin friction behavior with Reynolds number, as measured by oil film interferometry. [Preview Abstract] |
Sunday, November 22, 2009 9:18AM - 9:31AM |
AA.00007: Turbulence Measurements with Hot Wires in High Reynolds Number Boundary Layers J.H.M. Fransson, N. Hutchins, R. Oerlue, M. Chong During the last decade there has been a renewed interest in the
scaling of turbulent boundary layers, especially with regard to
the mean and fluctuation velocity distributions. Recently the
ICET team carried out velocity measurements in three different
wind tunnels (at KTH, Univ. Melbourne and IIT) for overlapping
Reynolds numbers in the range $11,000 |
Sunday, November 22, 2009 9:31AM - 9:44AM |
AA.00008: Study of turbulent boundary layer structures using Tomographic PIV Qi Gao, Ellen Longmire, Cecilia Ortiz-Duenas Tomographic-PIV was applied to investigate vortical structures in the logarithmic region of turbulent boundary layers. Measurements were performed in a water channel facility with $\delta \approx $110 mm for Re$_{\tau}\approx $2400 and 2900. Laser sheets with thickness up to 7mm were aligned parallel to the bounding surface. Four cameras with 2k x 2k pixels were placed in a rectangular array facing the measurement volume with tilt angle $\sim $30\r{ }to the wall normal direction. Magnification was $\sim $0.05 mm/pixel. The resulting measurement volumes were 0.8$\delta $ x 0.8$\delta $ in the streamwise and spanwise directions and 0.065$\delta $ or 120 viscous units in the wall-normal direction. Correlations were performed on 64$^{3}$ voxel volumes with 75{\%} overlap yielding a vector spacing of 25$^{3}$ viscous units. The data were probed using swirl strength and direction as well as convection velocity to identify and characterize relatively large scale eddies and structures within the volumes. The results will be discussed and compared with results at similar wall-normal locations in lower Reynolds number DNS channel (Re$_{\tau }$=590, 934 of Moser et al., 1999 and del \'Alamo et al., 2004) and wind tunnel (Re$_{\tau}$=1160) flows. [Preview Abstract] |
Sunday, November 22, 2009 9:44AM - 9:57AM |
AA.00009: Tomographic Particle Image Velocimetry Measurements of a High Reynolds Number Turbulent Boundary Layer Callum Atkinson, Michel Stanislas, Julio Soria Streamwise/wall-parallel volumes in the buffer region of a turbulent boundary layer at Re$_{\theta }$ =7800 and 11800 are measured using a 4 camera (2048 $\times $ 2048 px) tomographic particle image velocimetry (Tomo-PIV) system in the turbulent boundary layer wind tunnel at the Laboratoire de M\'{e}canique de Lille (LML). Measurement volumes of 1200 $\times $ 180 $\times $ 1200 pixels are achieved, the large boundary layer provided by this tunnel ($\delta \sim $ 0.3 m) resulting in volumes of 470$^{+} \times $ 70$^{+} \times $ 470$^{+}$ and 920$^{+} \times $ 140$^{+} \times $ 920$^{+}$ wall units, respectively. The quality of the data acquired by this technique is assessed based on the mean velocity profile, velocity fluctuations, velocity power spectrum and the fluctuating divergence. Streaks and streamwise vortices are examined and an attempt is made to classify the flow using the invariants of the full velocity gradient tensor. [Preview Abstract] |
Sunday, November 22, 2009 9:57AM - 10:10AM |
AA.00010: Flow Structures and Effects of Spatial Resolution on Turbulence Statistics in Rough Wall Turbulent Channel Flow Joseph Katz, Jiarong Hong, Michael Schultz PIV data obtained in the roughness sublayer of a turbulent channel flow is used for examining effects of spatial resolution on the magnitude, distribution, and trends of Reynolds stresses. Starting with a vector spacing of 63um (9-12 wall units), for roughness consisting of 0.45mm high pyramids at Re$_{\tau}$=3400-5418, spatial filtering of data causes major reduction in the magnitude of Reynolds stresses in the roughness sublayer. Although these reductions extend to well above the log layer, they increase with decreasing distance from the wall, especially for terms involving the wall-normal velocity fluctuation component, but also for the streamwise component. As expected, these effects increase with filter size, and are much higher for 2D filters in comparison to 1D ones. Consequently, trends of Reynolds stresses, and even mean flow profile vary significantly with filter properties. Spatial energy spectra and distributions of 2D swirling strength show the increasing role of small scale eddies on 2$^{nd}$ order statistics as the wall is approached, which is attenuated by filtering. [Preview Abstract] |
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