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 CB: Turbulent Boundary Layers II |
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Chair: Hyung Jin Sung, KAIST Room: Long Beach Convention Center 101B |
Sunday, November 21, 2010 1:00PM - 1:13PM |
CB.00001: Volumetric Velocimetry in Wall Bounded Flows Tristan Cambonie, Jean-Luc Aider The role od three-dimensional (3D) perturbations in the transition process of boundary layers is well- known. One of the major limitations in the understanding of the complex mechanisms involved in the transitions relies on the experimental difficulty in investigating strongly 3D unstationary flows. In this study, we apply for the first time Volumetric Velocimetry to a boundary layer flow. Volumetric Velocimetry gives access to the instantaneous three-components (3C) 3D velocity field (3D3C). It has already been applied to various detached vortical structures like vortex rings, but it is still a challenge in wall bounded flows because of the need of a good spatial resolution to resolve small-scale structures and because of the optical perturbations induced by the wall. We propose a dedicated experimental methodology adapted to these constraints and apply it succesfully to complex 3D flows induced by different three-dimensional perturbations introduced into a flat-plate boundary layer. [Preview Abstract] |
Sunday, November 21, 2010 1:13PM - 1:26PM |
CB.00002: Corrected Hot-wire Measurements of Stream-wise Turbulence Intensity from Several ZPG Boundary Layers Hassan M. Nagib, Richard D. Duncan, Peter A. Monkewitz Current experimental activity aimed at resolving the scaling of stream-wise turbulence intensity profiles $\overline{uu}(y)$ with Reynolds number in turbulent flat plate boundary layers has brought the largely unresolved issue of correcting systematic errors in hot-wire measurements of $\overline{uu}(y)$ into focus. Recently, we demonstrated the effectiveness of a heuristic scheme to generate unique $\overline{uu}^+ (y^+; Re_{\delta^*})$ profiles from selected data sets obtained with single hot-wires of widely different length, aspect ratio and construction over a large Reynolds number range of $4,000 < Re_{\delta^*} < 50,000$. The scheme has been applied to a larger number of data sets in zero pressure gradient (ZPG) boundary layers and is used here to re-examine the scaling of the stream-wise turbulence intensity profiles. These results confirm or reveal Reynolds number trends of features such as the peak intensity, in addition to pinpointing limitations of some of the data sets in the literature. The best scaling for $\overline{uu}(y)$ is examined in different parts of the boundary layer as a function of Reynolds number. [Preview Abstract] |
Sunday, November 21, 2010 1:26PM - 1:39PM |
CB.00003: Resolving the 3D velocity field inside a Roughness Sublayer in a turbulent channel flow using HPIV Siddharth Talapatra, Joseph Katz Microscopic holographic PIV is used to measure the 3D velocity field within
the roughness sublayer of a turbulent channel flow at Re$_{\tau }$ of 3400.
Recording holograms through a rough surface is facilitated by matching the
optical refractive index of the rough wall with that of the working fluid, a
concentrated solution of NaI in water. The pyramidal roughness height is
$k$=0.45mm, the sample volume size is 3.2$\times $1.8$\times $1.8mm$^{3}$, the
long dimension being in the streamwise direction, and the wall-normal range
is -0.33$ |
Sunday, November 21, 2010 1:39PM - 1:52PM |
CB.00004: A reinterpretation of the distribution of vortical structure in wall turbulence Beverley McKeon, Ian Jacobi, Ati Sharma The critical layer framework for turbulent pipe flow proposed by McKeon \& Sharma (\textit{J. Fluid Mech, 2010, see also the DFD-2010 presentation on `Structure from the critical layer framework in turbulent flow' by Sharma \& McKeon}) provides a model by which the distribution of hairpin-like vortices in wall turbulence can be reinterpreted. The model is used to demonstrate that the shear associated with the wall-normal variation of the mean velocity profile suppresses so-called retrograde vortices. Analysis of PIV images in the streamwise/wall-normal plane of a relatively low Reynolds number, zero pressure gradient turbulent boundary layer shows that the use of a Gallilean invariant decomposition of the velocity field prior to the calculation of swirl, i.e. subtraction of a constant convection velocity from the field, leads to a distorted count of the apparent number of retrograde spanwise vortices. By comparison, the result of a Reynolds decomposition suggests an essentially even distribution between prograde vortices (identified by many researchers as the heads of hairpin vortices) and retrograde ones, (i.e. vortices with the opposite sense of rotation) in agreement with the critical layer model. [Preview Abstract] |
Sunday, November 21, 2010 1:52PM - 2:05PM |
CB.00005: Non-intrusive measurements in hypersonic shock wave turbulent boundary layer interactions Anne-Marie Schreyer, Dipankar Sahoo, Alexander J. Smits Measurements are presented to describe the behavior of a shock wave turbulent boundary layer at hypersonic speed. Mean flow and two components of velocity fluctuations are obtained using PIV, and flow visualization and thermal imaging are performed using schlieren and infrared imaging, respectively. The boundary layer develops at Mach 7.2 in a perfect gas, at a Reynolds number based on momentum thickness between 3600 and 5500. The shock waves are created using two-dimensional compression corners of 8$^{\circ}$ and 33$^{\circ}$. The flow field is attached for the 8$^{\circ}$ corner, and separated for the 33$^{\circ}$ corner. The modification of the flow field due to micro-ramps placed upstream of the 33$^{\circ}$ corner is also discussed. [Preview Abstract] |
Sunday, November 21, 2010 2:05PM - 2:18PM |
CB.00006: Fully-resolved turbulence measurements in high Reynolds number pipe flow using a nano-scale probe Margit Vallikivi, Marcus Hultmark, Alexander Smits Statistics of the streamwise velocity component were measured at Reynolds numbers from $45 \times 10^3$ to $800 \times 10^3$ in the Princeton/ONR Superpipe. A nano-scale thermal anemometry probe (NSTAP) with sensing volume $60 \times 2 \times 0.1 \mu$m was used to obtain data that were free from the effects of spatial filtering. The results agree well with data from conventional measurement techniques for the lower Reynolds numbers but the NSTAP allows the study of fully resolved turbulence at Reynolds numbers almost one order of magnitude larger than conventional techniques. The data gives new insight on pipe flow turbulence, as well as providing a quantitative estimate of the the effects of spatial filtering, allowing for re-evaluation of previous datasets obtained with limited spatial resolution. [Preview Abstract] |
Sunday, November 21, 2010 2:18PM - 2:31PM |
CB.00007: Non-Local Geometry of High Reynolds Number Wall-Bounded Turbulence using Tomographic Particle Image Velocimetry Callum Atkinson, Michel Stanislas, Julio Soria Three-dimensional fields resulting from tomographic particle image velocimetry (Tomo-PIV) measurements in the buffer region of a fully developed flat plate turbulent boundary layer at Re$_{\theta} = 7800$ and 11800 are examined to extract statistics on the geometry and spatial distribution of large-scale coherent structures in wall bounded turbulence. Fields of $470^+ \times 70^+ \times 470^+$ and $920^+ \times 140^+ \times 920^+$ wall units are examined at a distance of $y^+ = 8$ to 55 and $y^+ = 15$ to 100 from the wall for Re$_{\theta} = 7800$ and 11800, respectively. Pattern recognition methods are used to extract and classify the structures. Results are compared with Stereo-PIV and direct numerical simulations of a boundary layer at Re$_{\theta} = 1950$. The enstrophy, dissipation and kinetic energy associated with each of these structures are considered. [Preview Abstract] |
Sunday, November 21, 2010 2:31PM - 2:44PM |
CB.00008: Time-resolved PIV in fully developed turbulent pipe flow Leo Hellstr\"om, Aman Sinha, Alexander Smits Stereoscopic particle image velocimetry was used to study the three-component velocity field in fully developed turbulent pipe flow, to investigate the structure and behavior of the large and very large scale motions in the outer layer. The data was acquired with a high speed camera, making it possible to resolve the velocity field in time for Reynolds numbers ranging from 1.3$\times$10$^{4}$ to 3.6$\times$10$^{4}$. The data corresponds to a displacement of approximately 20 diameters. The observed velocity fluctuations and the azimuthal two point correlations are consistent with previous studies, showing the existence of very large scale coherent structures. Proper Orthogonal Decomposition was performed on the data to further investigate the structures. [Preview Abstract] |
Sunday, November 21, 2010 2:44PM - 2:57PM |
CB.00009: Proper orthogonal decomposition of a decelerating turbulent boundary layer Murat Tutkun Our analysis is based only on streamwise component of velocity fluctuations since the data were simultaneously obtained using a hot-wire rake of 143 single wire probes. The experiment was carried out in the large wind tunnel of Laboratoire de M\'{e}canique de Lille whose test section is 20 m long, 2 m wide and 1 m high. A 2D bump was used to create converging-diverging flow inside the test section. The thickness of the boundary layer was 25 cm at the measurement location and Reynolds number based on momentum thickness, Re$_{\theta}$, was $17\:100$ for 10 m s\textsuperscript{-1} external free stream velocity measured before the bump. Eigenvalue distribution over POD modes shows that approximately 90\% of turbulence kinetic energy due to streamwise fluctuations within the domain was captured by the first 5 POD modes. The first POD mode carried more than 45\% of turbulence kinetic energy. Resulting eigenspectra are studied for different frequencies and spanwise Fourier indices in order to reduce the number of modes used in reconstructed velocity fields. [Preview Abstract] |
Sunday, November 21, 2010 2:57PM - 3:10PM |
CB.00010: Dynamic Perturbation of a Turbulent Boundary Layer and Experimental Identification of Critical-Layer-Type Behavior Ian Jacobi, Beverley J. McKeon A zero-pressure gradient turbulent boundary layer is perturbed by a spatially impulsive patch of two-dimensional roughness elements, which are actuated dynamically to alternate between smooth and rough surface conditions, and the downstream response is measured by hot-wire anemometry and particle image velocimetry. The dynamic perturbation is observed to contribute a periodic signature to the downstream flow-field, which manifests itself in critical-layer type behavior. The downstream flow field is reconstructed in a phase-locked sense in order to compare the observed behavior with asymptotic representations of the expected behavior at matched flow conditions. Perturbation using a periodic disturbance is shown to reveal underlying features of the turbulent boundary layer which are intimately connected to the critical layer framework for turbulent pipe flow proposed by McKeon \& Sharma (\textit{see the DFD-2010 presentation on `Structure from the critical layer framework in turbulent flow' by Sharma \& McKeon}), while simultaneously providing practical insight on the manipulation of the structure of boundary layers. [Preview Abstract] |
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