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 R19: Boundary Layers VIII: Experimental 
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Chair: Ellen Longmire, University of Minnesota Room: 310/311 
Tuesday, November 26, 2013 1:05PM  1:18PM 
R19.00001: Large field of view multiresolution experimental measurement of the spatial structure of a high Reynolds number turbulent boundary layer Nicolas A Buchmann, Callum Atkinson, Charitha de Silva, Ebenezer Gnanamanickam, Nicholas Hutchins, Julio Soria, Ivan Marusic A multiple camera, multiple resolution PIV system consisting of nine highe resolution cameras and two dual cavity lasers is used to instantaneously measure a large streamwise, wallnormal field of view (2$\delta \times 1.5\delta$), while simultaneously resolving the nearwall flow down to a height of y $+ \approx$ 3 at Reynolds numbers of Re$\tau \approx $ 8, 000 to 30, 000. The high spatial resolution in the nearwall vicinity enables direct estimation of the wall shear stress and allows for subsequent and conditional analysis of both the nearwall and larger outer flow structures and fluctuations. The quality of this measurement is assessed via statistical comparison with previous measurements made using hotwire anemometry and compared with the highest available Reynolds number DNS. Conditional twopoint correlations, and conditional mean structures will be presented. [Preview Abstract] 
Tuesday, November 26, 2013 1:18PM  1:31PM 
R19.00002: Turbulence measurements in high Reynolds number boundary layers Margit Vallikivi, Alexander Smits Measurements are conducted in zero pressure gradient turbulent boundary layers for Reynolds numbers from Re$_{\theta} =$ 9,000 to 225,000. The experiments were performed in the High Reynolds number Test Facility (HRTF) at Princeton University, which uses compressed air as the working fluid. NanoScale Thermal Anemometry Probes (NSTAPs) are used to acquire data with very high spatial and temporal precision. These new data are used to study the scaling behavior of the streamwise velocity fluctuations in the boundary layer and make comparisons with the scaling of other wallbounded turbulent flows. [Preview Abstract] 
Tuesday, November 26, 2013 1:31PM  1:44PM 
R19.00003: Effect of pressure gradient fluctuations on boundary layer turbulence Pranav Joshi, Joseph Katz, Xiaofeng Liu The present study focuses on the effect of largescale pressure gradient fluctuations on turbulence in both, zero pressure gradient (ZPG) and mean favorable pressure gradient (FPG) boundary layers. Timeresolved, twodimensional PIV data in the streamwisewallnormal plane enables us to calculate the instantaneous pressure distributions by integrating the planar projection of the material acceleration of the fluid. In both boundary layers, sweeps (u$^{\prime} $\textgreater\ 0, v$^{\prime} $\textless\ 0) mostly occur during periods of adverse pressure gradient fluctuations ($\partial $p$^{\prime} $/$\partial $x \textgreater\ 0), while favorable pressure gradient fluctuations ($\partial $p$^{\prime} $/$\partial $ x \textless\ 0) accompany ejections (u$^{\prime} $\textless\ 0, v$^{\prime} $\textgreater\ 0). Conditional averaging indicates that in the ZPG boundary layer, largescale $\partial $p$^{\prime} $/$\partial $x \textgreater\ 0 events accompanying sweeps lead to the formation of a growing region of ejection downstream, in a phenomenon resembling adversepressure induced flow separation. This phenomenon is much less pronounced in the FPG boundary layer, as the largescale $\partial $p$^{\prime} $/$\partial $ x \textgreater\ 0 events are for the most part significantly weaker than the mean FPG. Conditional sampling and instantaneous data in the ZPG boundary layer also confirm that although some of the ejections are preceded, and presumably initiated, by regions of adverse pressure gradients and sweeps, others are not. In the FPG boundary layer, there is no evidence of sweeps or adverse pressure gradients immediately upstream of ejections. The mechanisms initiating these structures presumably occur far upstream of the peak in favorable pressure gradient fluctuations. [Preview Abstract] 
Tuesday, November 26, 2013 1:44PM  1:57PM 
R19.00004: Boundary layer response to periodic spanwise perturbation by an array of obstacles Yan Ming Tan, Ellen Longmire Hotwire and stereoscopic particle image velocimetry (SPIV) measurements were performed on zero pressure gradient turbulent boundary layers perturbed by a single array of cylinders extending into the log region. The array spacing had a strong effect on the resulting vortex packet organization. With $0.6\delta $ array spacing, incoming vortex packets are frequently enhanced and remain stable over a downstream distance of $7\delta $. On the other hand, a $0.2\delta $ spacing strongly disturbed incoming packets initially, but the incoming organization frequently reappeared by $2\delta $ downstream. Measurements indicate that the effect of the perturbation is strongest in the midspan location between array elements. Furthermore, hotwire measurements suggest that the strongest velocity perturbations migrate upwards with increasing downstream distance. SPIV results in streamwisespanwise planes at different heights will be compared to show how structural aspects of the perturbation vary with downstream distance. [Preview Abstract] 
Tuesday, November 26, 2013 1:57PM  2:10PM 
R19.00005: Latest Developments on Obtaining Accurate Measurements with Pitot Tubes in ZPG Turbulent Boundary Layers Hassan Nagib, Ricardo Vinuesa Ability of available Pitot tube corrections to provide accurate mean velocity profiles in ZPG boundary layers is reexamined following the recent work by Bailey {\it et al}. Measurements by Bailey {\it et al.}, carried out with probes of diameters ranging from 0.2 to 1.89 mm, together with new data taken with larger diameters up to 12.82 mm, show deviations with respect to available highquality datasets and hotwire measurements in the same Reynolds number range. These deviations are significant in the buffer region around $y^{+}=3040$, and lead to disagreement in the von K\'arm\'an coefficient $\kappa$ extracted from profiles. New forms for shear, nearwall and turbulence corrections are proposed, highlighting the importance of the latest one. Improved agreement in mean velocity profiles is obtained with new forms, where shear and nearwall corrections contribute with around 85\%, and remaining 15\% of the total correction comes from turbulence correction. Finally, available algorithms to correct wall position in profile measurements of wallbounded flows are tested, using as benchmark the corrected Pitot measurements with artificially simulated probe shifts and blockage effects. We develop a new scheme, $\kappa B$Musker, which is able to accurately locate wall position. [Preview Abstract] 

R19.00006: ABSTRACT WITHDRAWN 
Tuesday, November 26, 2013 2:23PM  2:36PM 
R19.00007: Direct measurement of the velocity joint probability density function and higher order moments in turbulent boundary layer flows Julio Soria, Callum Atkinson This work shows how the joint probability density function (JPDF) of the streamwise and wall normal velocity components of a zeropressure gradient turbulent boundary layer (ZPGTBL) can be directly measured using the methodology and theoretical framework proposed by Soria \& Willert (2012) MST 23, 065301. Higher order moments including Reynolds stresses can be computed directly from twocomponent (2C) JPDFs of the streamwise and wall normal velocity components by taking moments of the 2CJPDF. The base data for the direct measurement of the 2CJPDF are singleexposed image pairs typically used to determine instantaneous 2C2D particle image velocimetry (PIV) fields. However, in the new direct measurement method, the instantaneous velocity samples necessary to build up the JPDF never need to be determined, which avoids the problems in PIV due to large velocity gradients that are typically encountered in turbulent wallbounded flows. This new method has been applied to singleexposed image pairs acquired over a range of Reynolds numbers ranging up to $Re_{\tau} = 19500$ in ZPGTBL experiments. This paper presents directly measured 2CJPDFs across the ZPGTBL as well as higher moment distributions determined from these 2CJPDFs. [Preview Abstract] 
Tuesday, November 26, 2013 2:36PM  2:49PM 
R19.00008: Measurement of entropy generation within bypass transitional flow Richard Skifton${}^{2}$, Ralph Budwig${}^{3}$, Donald McEligot, John Crepeau A flat plate made from quartz was submersed in the Idaho National Laboratory's Matched Index of Refraction flow facility. Particle Image Velocimetry and Particle Tracking Velocimetry were utilized to capture spatial vector maps at near wall locations \textit{within a transitional boundary layer}. Entropy generation was then calculated directly from measured velocity vector fields using an integral approach. Two flows were studied: a Zero Pressure Gradient (ZPG) and an Adverse Pressure Gradient (APG), with $\beta $ $\approx$ 0.039. Near the leading edge of the plate, the free stream turbulence intensity (FSTI) to drive bypass transition was 7.5\% and 4.25\% for the ZPG and APG, respectively. Towards the downstream side of the plate, the FSTI was 2.5\% and 3\% for ZPG and APG, respectively. The integral approach for entropy generation rate, within the transitional region of flow, will be utilized as a design parameter to systematically reduce losses. As a second observation, the entropy generation can be shown to predict the onset of transitional flow. [Preview Abstract] 
Tuesday, November 26, 2013 2:49PM  3:02PM 
R19.00009: Logarithmic Boundary Layers in Strong TaylorCouette Turbulence Detlef Lohse, Sander Huisman, Rodolfo Ostilla, Sven Scharnowski, Christian Cierpka, Christian K\"ahler, Roberto Verzicco, Chao Sun, Siegfried Grossmann We provide direct measurements of boundary layer profiles in highly turbulent TaylorCouette flow up to $Re = 2 \times 10^6$ using highresolution particle image velocimetry and particle tracking velocimetry, complemented by DNS data on the same system up to $Re = 10^5$. We find that the mean azimuthal velocity profile at the inner and outer cylinder can be fitted by the von K\'arm\'an log law, but with corrections due to the curvature of the cylinder, which we theoretically account for, based on the NavierStokes equation and a closure assumption for the turbulent diffusivity. In particular, we study how these corrections depend on the cylinder radius ratio and show that they are different for the boundary layers at the inner and at the outer cylinder. [Preview Abstract] 
Tuesday, November 26, 2013 3:02PM  3:15PM 
R19.00010: Logarithmic region of turbulent boundary layer from low to high Reynolds numbers Yuki Wada, Yoshiyuki Tsuji Recent high Reynolds number experiments indicate that von Karman constant ($\kappa )$ is close to 0.38. In the classical moderate Reynolds number experiments, however, show the value of $\kappa =$0.41. In this study we would like to discuss the discrepancy between these two values. Analyzing the data in the range of 1500\textless Re$_{\mathrm{\theta }}$\textless 27300, we suggest the idea of Quasi Logarithmic Region (QLR) in which the log law is approximately satisfied and discuss the above issue. Using the QLR, we report the Reynolds number dependence of $\kappa $, and recommend the appropriate loglaw region. [Preview Abstract] 
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