Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session FE: Turbulence: Boundary Layers III (Non-canonical) |
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Chair: P.H. Alfredsson, The Royal Institute of Technology, Sweden Room: Salt Palace Convention Center 151 D-F |
Monday, November 19, 2007 8:00AM - 8:13AM |
FE.00001: Investigation of a Pulsating Channel Flow with Strong Bulk Flow Reversal Using Particle Image Velocimetry Sean Kearney, Thomas Dimiduk, Timothy O'Hern, Jesse Roberts, Jeremy Barney, Thomas Grasser Variable-time-delay PIV is used to characterize a pulsating channel flow with strong bulk reversal. Low- and high-magnification fields of view are used to reveal the nature of the flow across the full channel height and to resolve the velocity profile in the viscous sublayer. Results are presented for \textit{Re}$_{d}$ = 1.1 $\times $ 10$^{4}$, based on the time-mean velocity, for two values of the forcing frequency (5 and 10 Hz or \textit{$\omega $}$^{+}\sim $ 2.5 and 5.0 $\times $ 10$^{-4})$, and for two cases of strong bulk flow reversal ($\,{\left( {U_{\max } \,-\,U_{\min } } \right)} \mathord{\left/ {\vphantom {{\left( {U_{\max } \,-\,U_{\min } } \right)} {U_{\mbox{mean}} }}} \right. \kern-\nulldelimiterspace} {U_{\mbox{mean}} }$= 4 and 8). The frequency is low enough for the pulsations to impact the turbulence across the full channel height. PIV realizations at low magnification reveal relaminarization during periods of strong acceleration which is followed by transition and turbulence during weakly accelerating and decelerating portions of the cycle. The phase-evolution of the velocity profiles, wall shear stress and turbulence quantities are discussed. The results show that logarithmic time-mean velocity profiles may persist in spite of the strong departure of the flow from equilibrium turbulence over much of the cycle, and that relaminarization weakens the wall shear stress modulation. [Preview Abstract] |
Monday, November 19, 2007 8:13AM - 8:26AM |
FE.00002: Effect of periodic wakes on jets injected into turbulent boundary layers Ralph Volino Surfaces subject to high temperature flow are often cooled using lower temperature jets injected through the surface. The jets typically have low velocity and are inclined at shallow angles so that they remain near the surface, forming a protective film. The technique is known as ``film cooling.'' The process can be complicated by periodic turbulent wakes shed from objects moving upstream of the cooled surface. In the present study, jets with various velocities were injected into turbulent boundary layers on a flat-plate test wall. Periodic wakes were generated with a spoked wheel, located upstream in the wind tunnel. The jet behavior was determined through instantaneous flow temperature measurements made with a traversing cold-wire (constant current) probe. The measurements were ensemble averaged to show the temperature field at various phases during the wake passing cycle. The wakes tend to force the jets closer to the surface, enhancing their cooling effectiveness, but the associated turbulence has the opposite effect and accelerates coolant dispersal. The net effect depends on the jet velocity. Results, including animations of the experimentally measured flow temperature fields, will be presented. [Preview Abstract] |
Monday, November 19, 2007 8:26AM - 8:39AM |
FE.00003: PIV measurements of the velocity field in counter-rotating cylindrical Couette flow Rene van Hout, Joseph Katz An experimental investigation using Particle Image Velocimetry (PIV) was carried out to study the latitudinal planar velocity field in air counter-rotating cylindrical Couette flow at high Reynolds numbers. The facility consisted of two concentric cylinders with a radius ratio of $\eta ={r_i } \mathord{\left/ {\vphantom {{r_i } {r_o }}} \right. \kern-\nulldelimiterspace} {r_o }$= 0.55 and aspect ratio $\Gamma =L/\left( {r_o -r_i } \right)$= 11.2. Measurements were done at two outer cylinder Reynolds numbers, R$_{o}$ = -25,196 and -52,042 while the inner cylinder Reynolds number varied between R$_{i}$ = 2,635 to 40,446. At constant R$_{o}$ with increasing R$_{i}$, the mean azimuthal velocity profile became increasingly flatter over most of the annulus with a strong shear layer near the cylinder wall. The radius at which $U_{\theta }$ changed sign moved away from the inner cylinder. Plotted against inner wall coordinates, the azimuthal velocity profile displayed log law behavior albeit with increased values of \textit{$\kappa $} and $B$ as R$_{i}$ was increased. Normalized rms values of the azimuthal fluctuating velocity component and Reynolds stresses peak near to the wall. Magnitudes increase and become more significant over the whole width of the annulus as R$_{i}$ increased. Higher moments display double peaks. Holding the inner cylinder rotation speed constant while increasing the outer cylinder speed strongly influenced the radial profiles of turbulent stresses. [Preview Abstract] |
Monday, November 19, 2007 8:39AM - 8:52AM |
FE.00004: Turbulent swirling layer with free surface Philippe Bardet, Per Peterson, Omer Savas A turbulent annular liquid wall jet, or vortex tube, generated by helical injection inside a tube was characterized experimentally. The resulting hollow confined swirling layer is proposed for use in a thick liquid first-wall chamber concept for inertial fusion power plants. The velocity fields were measured with a single camera split-screen stereoscopic particle image velocimetry scheme. The flow was studied at 5 stations between 1.5 and 4.5 ``vortex tube'' diameters downstream of the injection nozzle in a horizontal plane that coincides with the tube axis. Up to 1024 independent realizations were recorded and analyzed for Reynolds numbers ranging from 3,200 to 14,000 at each station. The turbulent structures are non-isotropic and non-homogeneous. Gradients in average velocity and Reynolds stress result in turbulent kinetic energy production. Between 1.5 and 3.5 diameters, the average azimuthal velocity profile alone is non uniform away from the wall. Persistent large vortical structures are observed. The turbulent kinetic energy decreases slowly with distance while the dissipation decreases rapidly. At 4.5 diameters, the wall effect influences strongly the average velocity profiles. The vortical structures disappear and the turbulent kinetic energy increases. [Preview Abstract] |
Monday, November 19, 2007 8:52AM - 9:05AM |
FE.00005: Turbulent Flow Through 90 Degree Pipe Bends Guangjun Cao, Metodi Zlatinov, Alexander Smits A fully developed turbulent pipe flow is directed through a 900 bend with two different radii of curvature. Particle image velocimetry (PIV) is used to measure the streamwise and radial components of velocity far upstream, immediately upstream, immediately downstream, and far downstream of the bend. The velocity and vorticity maps from each of the four locations are used to illustrate the progress of secondary motion created by the bend. The number, arrangement and strength of the streamwise vortices created by the bend is analyzed as a function of the Reynolds number, and the ratio of pipe radius to the radius of curvature of the bend. Preliminary results from measurements upstream of the bend show that for Reynolds numbers up to 4 , the fully developed velocity profile is symmetric at a distance of 15 internal pipe diameters upstream of a bend that has a curvature radius ratio of 1, but the flow near the outside wall of the pipe slows down as it approaches the bend. This effect is more important at lower Reynolds numbers. Measurements at higher Reynolds numbers will be reported at the meeting. [Preview Abstract] |
Monday, November 19, 2007 9:05AM - 9:18AM |
FE.00006: Unsteady wall-pressure loading in a Mach 3 compression ramp flow at $Re_{\theta}=2400$. Matthew Ringuette, Alexander Smits We perform experiments to investigate the unsteady wall-pressure behavior in a Mach 2.9 shock-wave turbulent boundary layer interaction. The flow configuration is a nominally two-dimensional $24^{\circ}$ compression ramp, and the Reynolds number based on momentum thickness is 2400. In contrast to measurements at higher Reynolds numbers (of order $10^4$--$10^5$), the results show a smaller peak in the RMS of the wall-pressure fluctuations, and the wall-pressure signal exhibits a much richer intermittency in the shock-foot region. Spectra show that the signal energy is more evenly distributed over the range of shock oscillation frequencies, resulting in a smaller peak energy than that found at higher Reynolds numbers. The shock motion has a broadband frequency distribution with a peak slightly below 1 kHz, similar to the higher Reynolds number data. We find good agreement with the direct numerical simulation of Wu~\&~Mart\'{\i}n\footnote{Wu, M. \& Mart\'{\i}n, M. P. Direct numerical simulation of supersonic turbulent boundary layer over a compression ramp. \textit{AIAA Journal} \textbf{45}(4), 2007, 879--889.} at matching conditions. [Preview Abstract] |
Monday, November 19, 2007 9:18AM - 9:31AM |
FE.00007: Upstream and downstream influence on shock and turbulent boundary layer interactions Stephan Priebe, Minwei Wu, M. Pino Martin Direct numerical simulation data of a Mach 3, $Re_{\theta}=2300$ turbulent boundary layer interacting with various shockwave configurations are considered. The shock unsteadiness is presented and correlations between the incoming flow and the shock motion, as well as the downstream flow and the shock unsteadiness are presented. Analyses on a compression corner configuration (Wu \& Martin, 2007 \footnote{Wu, M., Martin, M.P., ``Analysis of shock motion in shockwave/turbulent boundary layer interaction using DNS data,'' Accepted for publication in Journal of Fluid Mechanics, 2007.}) show that the unsteadiness of the separation bubble correlates with the low-frequency of the shock motion, giving a Strouhal number of 0.8 based on the low-frequency of the shock motion, the length of the separation bubble and the average maximum velocity of reversed flow. This scaling is assessed further in a reflected shock configuration. [Preview Abstract] |
Monday, November 19, 2007 9:31AM - 9:44AM |
FE.00008: Measurements in a boundary layer with intense free stream turbulence. Nicole Sharp, Stephanie Neuscamman, Sergiy Gerashchenko, Zellman Warhaft A high Reynolds number boundary layer with free stream turbulence up to a Taylor-scale Reynolds number of order 1,000 was produced in a wind tunnel using both active and passive grids. The flow's velocity structure including spectra, co-spectra and probability density functions was mapped using hot-wire anemometry. We found that the transverse velocity variance decreased in the boundary layer, confirming earlier work by Hancock and Bradshaw (J. Fluid Mech., 205, 1989) and Thole and Bogard (J. Fluids Eng., 118, 1996) as well as other recent experimental work. The free stream turbulence Reynolds number, the level of free stream turbulence intensity, and the relative length scales of the boundary layer and free stream turbulence are varied using active and passive grids. [Preview Abstract] |
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