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 NQ: Turbulence: Shear Layers II |
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Chair: Jonathan Naughton, University of Wyoming Room: Salt Palace Convention Center 251 E |
Tuesday, November 20, 2007 11:35AM - 11:48AM |
NQ.00001: An experimental study of an annular jet with zero blockage ratio James Harlan, Douglas Smith An annular jet with zero blockage ratio was created at the exit of a tube with a dielectric barrier-discharge plasma actuator. The plasma actuator creates an annular wall jet along the interior surface of the tube and just inside of the tube exit. At the exit of the tube, the wall jet becomes an annular free jet with no flow blockage interior to the annulus. Particle image velocimetry measurements were made in a plane bisecting the jet axis. The velocity fields reveal an annular jet that grows preferentially towards the axis of the jet. Streamtraces obtained from the mean velocity field reveal that the fluid interior to the jet is drawn along the jet axis and radially outward as the annular jet entrains fluid. Contours of the streamwise component of the velocity reveal a region of nearly stagnant fluid interior to the annular jet just upstream of the merging of the annular jet shear layers. [Preview Abstract] |
Tuesday, November 20, 2007 11:48AM - 12:01PM |
NQ.00002: PIV Measurements in Turbulent Impinging Jets of Dilute Polymer Solutions R. Mejia-Alvarez, K.T. Christensen Turbulent impinging jets are commonly employed in technological applications like drying, scouring, cooling and heating because of high heat-transfer rates achievable in the impingement region. This effort explores a possible modification of turbulence (and therefore transport) in this flow configuration through the addition of a small amount of polymer to a submerged turbulent impinging water jet at Re~$\cong $~24,000 and a nozzle-to-plate spacing of 6$D$, where $D$ is the exit diameter of the jet nozzle. Particle image velocimetry (PIV) is used to acquire large ensembles of instantaneous velocity fields in an impinging jet with plain water as well as two different dilute solutions of polyethylene oxide (50 and 100~ppm). A high-resolution (4k~$\times $~2.75k pixels) CCD camera is employed to simultaneously resolve the flow in the region between the jet exit and the impingement surface as well as several diameters of the wall jet formed by this flow configuration. The statistical character of the turbulence in the jet-development, impingement and wall-jet regions is contrasted between the plain water and polymer solution cases. The dominant structural features of these flow regions are also identified and compared. [Preview Abstract] |
Tuesday, November 20, 2007 12:01PM - 12:14PM |
NQ.00003: Three Component LDA Measurements in Swirling Jets Richard Semaan, Jonathan Naughton Previous studies of swirling jets have revealed faster growth rates in the near field in comparison to their non-swirling counterparts. Recently, the growth rates and turbulent properties of the swirling jet in the far field have been shown to relax to those of the non-swirling jet. The current effort seeks to bridge these two regions by performing velocity surveys in the near and far field of a Re=100000 swirling jet using three-component Laser Doppler Anemometry (LDA). Surveys are performed for various levels of swirl number, the ratio of angular momentum flux to linear momentum flux, from 0 to 0.4. Two different exit swirl profiles are studied, and the measurements are carried out in a region from the nozzle exit to 40 diameters downstream. In addition to bridging the near- field and far-field results, the mean data and turbulence statistics provide the means to examine the relaxation of these jets to their far-field form. Further, the separation of the axial and tangential flows and the scaling suggested by Ewing may be evaluated. [Preview Abstract] |
Tuesday, November 20, 2007 12:14PM - 12:27PM |
NQ.00004: Experimental Evaluation of Swirling Jet Growth Rate Enhancement Bryon Riotto, Richard Semaan, Jonathan Naughton The growth rate in the developing region of a free jet with swirl is known to be a function of the swirl number $S$, the ratio of the angular momentum flux to the axial momentum flux. At low swirl numbers, the growth rate is relatively unaffected, and at high swirl numbers the growth rate becomes saturated. Planar Mie Scattering (PMS) is used to determine the degree of growth rate enhancement due to swirl at Reynolds numbers of 50,000 and 100,000 and over a range of swirl numbers from 0.0 $< S <$ 0.4 in increments of 0.025. The swirl numbers at the nozzle exit for all of the cases are determined from velocity profiles measured using a two-component Laser Doppler Anemometer. Growth rates are calculated from the PMS flow visualization images over a range of 6 to 14 nozzle diameters. Two different swirl profiles, solid body rotation and a q- vortex, are examined. The level of swirl where the growth rate becomes a strong function of swirl, its behavior with increasing swirl, and where it becomes saturated are resolved in this study. [Preview Abstract] |
Tuesday, November 20, 2007 12:27PM - 12:40PM |
NQ.00005: A low-dimensional analysis of the axisymmetric jet:identification and control Mark Glauser, Andre Hall, Jeremy Pinier The endeavor of prediction and ultimate control of highly turbulent, non-linear, flow physics is undertaken using a 2-inch diameter, axisymmetric, jet nozzle operating at Mach 0.60 exit condition. With the aim of identifying the dominant source of the radiated aero-acoustic noise produced by high-speed, heated jets and developing control strategies to reduce it, two primary experiments are led in parallel: 1) A non-intrusive PIV investigation of the flow field (z/D=5-10) is performed, both for the heated jet (static temperature ratio T$_{r}$=1.72) and ambient temperature jet (T$_{r}$=0.93), simultaneously with near-field pressure and far-field acoustic measurements to assess the effect of heat on low-dimensional source identification 2) Dual-time PIV investigation of the sound producing region (z/D=3-10), (T$_{r}$=0.93), is performed to capture the instantaneous Eulerian acceleration field and used to derive an empirical low-order dynamical system (LODS) for eventual use in closed-loop flow control applications. This effort aims to acquire an extensive database that can be used to develop a greater understanding of the dynamics in a highly random, turbulent flow field. This understanding is vital in determining which features of the flow a control strategy will manipulate, or what signals to feed back in elaborate closed-loop applications. [Preview Abstract] |
Tuesday, November 20, 2007 12:40PM - 12:53PM |
NQ.00006: High Reynolds Number Flows about Bodies of Revolution Juan Jimenez, Alexander Smits Measurements were conducted in the wake of a DARPA SUBOFF submarine model at a large range of Reynolds numbers based on model length, $1.1 \times 10^6 \leq \mathrm{Re_L} \leq 25 \times 10^6$, along the centerline of the wake for 5 different locations. The model is an axisymmetric body without appendages (fins) supported by a streamlined support. In addition, the pressure was measured at 45 different locations along the surface of the model. For all Reynolds numbers studied, the mean velocity distribution becomes self-similar between 3 and 6 diameters, $D$, downstream for the side where the support is not located. In contrast, none of the Reynolds stresses attain self similarity. For the higher Reynolds numbers studied the presence of the support introduces an asymmetry into the wake which results in the overall decrease of radial and axial turbulence intensities for the support side. Also, the coefficient of pressure, $\mathrm{C_P}$, distribution along the top meridian line of the model, $r/D > 0$, is generally lower for Re$_{\mathrm{L}}$ = $1.1 \times 10^6$ than that for Re$_{\mathrm{L}}$ = $12 \times 10^6$ and $25 \times 10^6$, which seem to have collapsed. [Preview Abstract] |
Tuesday, November 20, 2007 12:53PM - 1:06PM |
NQ.00007: Vortex dynamics in a turbulent shear flow over a cavity at near-zero Mach number Shiyao Bian, Steven Ceccio, James Driscoll A kilohertz frame-rate Cinematographic Particle Imaging Velocimetry system was used to acquire time series of whole-field velocity data for an incompressible, turbulent shear flow over a rectangular, shallow cavity with Re$_{L}$ = 2.87 $\times $ 10$^{5}$, where L is the cavity length. The cavity shear layer was divided into three regions that exhibited different vortex dynamics: formation, convection/evolution, and impingement. The second region is similar to a free shear layer, with vortex roll-up that is well predicted by linear, inviscid instability theory. The impinging shear layer produces a jet-like flow along the downstream wall, resulting in a large-scale recirculation zone in the cavity. This flow impinges on the shear layer in the formation region, increasing the shear layer growth rate. No self-sustained pressure or flow-field oscillations were observed for a variety of flow speeds. The dynamics of the shear layer in the impingement region was found to be correlated with the dynamic pressure on the downstream wall. [Preview Abstract] |
Tuesday, November 20, 2007 1:06PM - 1:19PM |
NQ.00008: Flow Field in the Near Wake of a Disk and Cup Elham Ghaem-Maghami, Kenneth Desabrais, Hamid Johari To investigate the flow field in the near wake of axisymmetric bluff bodies with fixed separation location, experiments with a disk and smooth cup were conducted in a water tunnel at a Reynolds number of 3.2~$\times $~10$^{4}$ and in a wind tunnel at a Reynolds number of 1.9~$\times $~10$^{5}$. The velocity field in the water tunnel was measured by the stereo particle image velocimetry technique while a hot-wire was used in the wind tunnel. Data were collected over an axial range extending to 9 diameters downstream. The mean and fluctuating velocity fields were measured for both Reynolds numbers while Reynolds shear stresses were measured only in the water tunnel. Streamlines computed from the average velocity field revealed that the recirculation zone extends to approximately 2 diameters downstream. The mean velocity deficit profiles for the cup and disk had very similar behavior beyond 3 diameters, but the cup wake appears to recover quicker than the disk. The turbulent shear stress and fluctuating velocity profiles were also very comparable between the cup and disk. The Reynolds number had a weak effect on the flow field, at least for the two values considered. [Preview Abstract] |
Tuesday, November 20, 2007 1:19PM - 1:32PM |
NQ.00009: Effects of flow parameters on bluff body near wake structures associated with base drag Vibhav Durgesh, Jonathan Naughton, Stephen Whitmore Recent studies have confirmed that the base drag on a bluff body can be reduced by modifying the boundary layer thickness and that changes in the near wake structures are responsible. However, these previous investigations did not identify the exact nature of the structure changes and their dependence on Reynolds number and boundary layer parameters. To address these issues, measurements have been performed on wedge and flat plate models including hot-wire measurements upstream of separation, pressure measurements in the base area, and Particle Image Velocimetry (PIV) measurements in the near wake. These measurements are used to determine boundary layer parameters, base drag reduction coefficients, and near wake large scale coherent structures using Proper Orthogonal Decomposition (POD). Previous publications have discussed that, in some cases, the vortical structures in the wake become weaker and become more organized as the boundary layer thickens. Here, the focus is on characterizing the wake parameters and their dependence on Reynolds numbers and boundary layer parameters as well as the corresponding base drag coefficients. The results show that the wake parameters are related to the boundary layer parameters, but they have an additional dependence on the Reynolds number. [Preview Abstract] |
Tuesday, November 20, 2007 1:32PM - 1:45PM |
NQ.00010: Measurement of Pressure-Rate-of-Strain, Pressure Diffusion and Velocity-Pressure-Gradient Tensors in a Cavity Shear Layer by Integrating the Material Acceleration Xiaofeng Liu, Joseph Katz A non-intrusive measurement technique that is capable of simultaneously measuring the instantaneous velocity, material acceleration and pressure distribution over a sample area has been applied to measure the pressure related turbulence statistics of a 2D open cavity flow. This technique utilizes four-exposure PIV to measure the distribution of material acceleration, and integrating it by means of circular virtual boundary omni-directional algorithm to obtain the instantaneous pressure distribution. Results enable direct measurements of components of the pressure-rate-of-strain, pressure diffusion and velocity-pressure-gradient tensors. Analysis of error propagation and comparisons between these terms indicate that the results are reliable. In the cavity shear layer, the pressure-rate-of-strain term R11 is mostly negative while R22 is positive but with smaller magnitude, implying that the streamwise turbulent energy is redistributed to the lateral direction. Conventional pressure-strain turbulence models are also compared with the measurement data. [Preview Abstract] |
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