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 KL: Turbulent Boundary Layers IV |
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Chair: Ellen Longmire, University of Minnesota Room: Tampa Marriott Waterside Hotel and Marina Meeting Room 8 |
Monday, November 20, 2006 5:15PM - 5:28PM |
KL.00001: Zero Pressure Gradient Flat Plate Boundary Layer Experiments Using Synchronized PIV and a Hot Wire Anemometry Rake M. Tutkun, P.B.V. Johansson, W.K. George, M. Stanislas, J.M. Foucaut, J. Kostas, S. Coudert, J. Delville Zero pressure gradient flat plate boundary layer experiments have been performed in the 20 meter long test section of the Laboratoire de M\'{e}canique de Lille, LML, wind tunnel. Measurements were carried out at Re$_{\theta}=$10 000 and Re$_{\theta}=$20 000 using synchronized PIV and a hot wire anemometry rake. The boundary layer thickness at the measurement location was about 30 cm. A hot wire rake of 143 probes was placed in the test section of the wind tunnel to provide the time history of the boundary layer. 2 stereo PIV systems in the wallnormal-spanwise (YZ) plane, and 1 stereo PIV system to record in the streamwise-wallnormal (XY) were used. One high repetition PIV system was used in streamwise-spanwise (XZ) plane. The sampling frequency of the XZ PIV system was 3000 VF/s at Re$_{\theta}=$20 000 and 1500 VF/s at Re$_{\theta}=$10 000. [Preview Abstract] |
Monday, November 20, 2006 5:28PM - 5:41PM |
KL.00002: Adverse Pressure Gradient Boundary Layer Experiments Using Synchronized PIV and a Hot Wire Anemometry Rake P.B.V. Johansson, M. Tutkun, W.K. George, M. Stanislas, J.M. Foucaut, J. Kostas, S. Coudert, J. Delville This is the first report of an adverse pressure gradient turbulent boundary layer experiment performed in Laboratoire de M\'{e}canique de Lille, LML, wind tunnel which is of 20 meter in length. The adverse pressure gradient was created by means of a bump of 30 cm height. The thickness of the boundary layer was about 30 cm and Reynolds number based on momentum thickness, Re$_{\theta}$, was 30 000 for 10 m/s external free stream velocity. A hot wire rake of 143 probes synchronized and simultaneously sampled together with 2 stereo PIV systems in the wallnormal-spanwise (YZ) plane, 1 cm upstream of the wires plane, and 1 stereo PIV system to record in the streamwise-wallnormal (XY) plane. One high repetition PIV system was used in streamwise-spanwise (XZ) plane with sampling frequency of 3000 VF/s and also at a slower rate simultaneously with hot wire signal. [Preview Abstract] |
Monday, November 20, 2006 5:41PM - 5:54PM |
KL.00003: Measurement of the Force Balance in Favorable Pressure Gradient Turbulent Boundary Layers Meredith Metzger, Adam Lyons, Paul Fife Well resolved multi-sensor hot-wire measurements were obtained in a favorable pressure gradient turbulent boundary, generated by tilting the ceiling of a low speed wind tunnel at a constant angle of 1.3$^\circ$. The experimental setup allowed direct measurement of all of the terms in the force balance as a function of wall-normal distance, streamwise location, and Karman number. The nature of the pressure gradient was such that the flow achieved equilibrium conditions at a streamwise location about three-quarters of the distance down the test section. Data from the present experiments are compared to available direct numerical simulations of the equilibrium case at much lower Reynolds number. Profiles of statistical quantities (mean, rms, Reynolds stress) as well as the ratio of terms in the force balance are analyzed for effects due to both non-equilibrium and acceleration parameter. Results are compared to theoretical predictions where appropriate. [Preview Abstract] |
Monday, November 20, 2006 5:54PM - 6:07PM |
KL.00004: High-Reynolds-number flat-plate turbulent boundary layer measurements Eric S. Winkel, James M. Cutbirth, Marc Perlin, Steven L. Ceccio, David R. Dowling A set of experiments was conducted in the U.S. Navy's Large Cavitation Channel (LCC) into the characteristics of a liquid turbulent boundary layer at nearly zero-pressure-gradient. The hydraulically smooth, k$^{+ }<$ 0.2, flat-plate test model measured 12.9 m in length and 3.05 m in span and was approximately centered in the LCC test section. Data was gathered at flow speeds up to 20 m/s to achieve downstream-distance-based Reynolds numbers up to 220 million. Static pressure, skin-friction, and laser-Doppler velocimetry (LDV) measurements are presented. Static pressure measurements along the plate surface show a mild favorable pressure gradient, less than 2.5{\%} flow acceleration over the model. Skin-friction was measured at six stream-wise positions with 15-cm-diameter, flush-mounted drag-balances. Flow profiles of the mean and second-order turbulence statistics of stream-wise and wall-normal velocity components were measured using two-component LDV. When normalized with the measured skin-friction, mean velocity profiles agree with the accepted law-of-the-wall constants and the total near-wall shear stress approaches unity. [Preview Abstract] |
Monday, November 20, 2006 6:07PM - 6:20PM |
KL.00005: High speed PIV measurements in the logarithmic region of a turbulent boundary layer Anurag Singh, Ellen Longmire, Ivan Marusic The existence of long low speed regions in the logarithmic region of turbulent boundary layers has been studied previously; most recently using spanwise arrays of hot-wires. Currently, we are using high speed PIV to characterize these low speed regions. Experiments were conducted in the logarithmic region of the turbulent boundary layer in a zero pressure gradient flow at friction Reynolds number $Re_\tau=1160$ with a streamwise-spanwise field of view of dimension 1.2$\delta$. A high speed camera and laser were used to obtain velocity fields at repetition rates ranging from 250 Hz to 1000 Hz. Sets of these fields were used to compute ensemble averaged statistics. Also, sections of consecutive fields were stitched end-to-end to form longer vector fields. This allows us to test, in part, the validity of using Taylor's hypothesis in this flow. Within the field of view, low speed regions of up to 14$\delta$ in length have been observed. In general, these low speed regions meander and some go out of the field of view in the spanwise direction. An algorithm is being developed to identify these regions automatically from the PIV results and to characterize their length scales. [Preview Abstract] |
Monday, November 20, 2006 6:20PM - 6:33PM |
KL.00006: Use of dual plane PIV to assess scale-by-scale energy budgets in wall turbulence Neelakantan Saikrishnan, Ellen Longmire, Ivan Marusic Dual plane particle image velocimetry (PIV) data are acquired in streamwise-spanwise planes in the logarithmic region of the turbulent boundary layer in a zero pressure gradient flow at friction Reynolds number $Re_\tau = 1160$. The dual plane technique allows determination of the full velocity gradient tensor in the measurement plane. In earlier work, data were acquired in fields of size $1.1\delta$ by $1.1\delta$ and velocities were resolved to areas of $25$ viscous wall units. This resolution was found to be adequate for identification of the energy-containing vortical structures. In current work, we repeat the experiments using smaller fields of size $0.5\delta$ by $0.5\delta$ in order to capture and investigate smaller scales. The combined data from both fields can be used to assess scale-by-scale energy budgets including the turbulent dissipation rate. The experimental results will be compared with results from a direct numerical simulation (DNS) of a fully developed channel flow at $Re_\tau = 934$. [Preview Abstract] |
Monday, November 20, 2006 6:33PM - 6:46PM |
KL.00007: High Resolution 3D Experimental Investigation of Flow Structures and Turbulence Statistics in the Viscous and Buffer Layer Jian Sheng, Edwin Malkiel, Joseph Katz Digital Holographic Microscopy is implemented to perform 3D velocity measurement in the near-wall region of a turbulent boundary layer in a square channel over a smooth wall at Re$_{\tau }$=1,400. The measurements are performed at a resolution of $\sim $1$\mu $m over a sample volume of 1.5x2x1.5mm (x$^{+}$=50, y$^{+}$=60, z$^{+}$=50), sufficient for resolving buffer layer structures and for measuring the instantaneous wall shear stress distributions from velocity gradients in the sublayer. The data provides detailed statistics on the spatial distribution of both wall shear stress components along with the characteristic flow structures, including streamwise counter-rotating vortex pairs, multiple streamwise vortices, and rare hairpins. Conditional sampling identifies characteristic length scales of 70 wall units in spanwise and 10 wall units in wall-normal direction. In the region of high stress, the conditionally averaged flow consists of a stagnation-like sweeping motion induced by a counter rotating pair of streamwise vortices. Regions with low stress are associated with ejection motion, also generated by pairs of counter-rotating vortices. Statistics on the local strain and geometric alignment between strain and vorticity shows that the high shear generating vortices are inclined at 45\r{ } to streamwise direction, indicating that vortices are being stretched. Results of on-going analysis examines statistics of helicity, strain and impacts of near-wall structures. [Preview Abstract] |
Monday, November 20, 2006 6:46PM - 6:59PM |
KL.00008: The structure of the sink flow turbulent boundary layer O.N. Ramesh, S. Manisekaran, Dixit Shivsai Ajit It is well known that the two-dimensional sink flow turbulent boundary layer is the only smooth wall flow configuration that satisfies the requirements of equilibrium (in the sense of Townsend (1956) and Rotta (1962)). Previous studies in the literature have looked in great detail the evolution of integral and turbulence quantities. The present experimental study is aimed at studying the structure of the sink flow turbulent boundary layer and more specifically with a view to understand the connection between equilibrium and the interaction between inner and outer regions. The sink flow studied has an acceleration parameter of K = 1.38E-6. Hotwire anemometry has been used for measurements. Mean velocity and longitudinal turbulence intensities were measured at 11 streamwise stations. It is observed that the mean velocity approaches equillibrium upstream of turbulence intensity. Coles wake parameter was seen to be equal to zero in the region of equilibrium. Higher order moments of streamwise velocity fluctuations are also presented for the sink flow. In the inner region there are some similarities in the skewness and flatness distributions between the sink flow and a zero pressure gradient turbulent boundary layer, whereas in the outer region they are very different. We seek to link the observed differences of higher order moments in the outer region to the structural differences between these two flows. [Preview Abstract] |
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