Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session AS: Turbulent Jets and Wakes |
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Chair: Mark Glauser, Syracuse University Room: Hilton Chicago Stevens 4 |
Sunday, November 20, 2005 8:00AM - 8:13AM |
AS.00001: Entrainment and Dilution in Isolated Turbulent Puffs Elham Ghaem-Maghami, Hamid Johari The flow field of isolated turbulent puffs was examined experimentally using the laser Mie scattering and Particle Image Velocimetry techniques. Puffs were generated by injecting air through a 5 mm diameter nozzle into a flow chamber with a weak coflow. The injection time was varied from 20 ms to 161 ms by a fast-response solenoid valve. Injection volumes corresponding to these times ranged from 6 to 58 cc. Past work has indicated that the mixing of burning puffs scales with the cube root of the injected volume. Isolated puffs with injection Reynolds number of 5,000 were examined in the range of 25 -- 40 diameters downstream of the nozzle. The results indicate that as the injection volume and time increases, puffs evolve from a spherical geometry to an axially elongated form. The velocity field inside the puff consists of a toroidal vortex. For the elongated puffs, the vortex is followed by a jet-like flow. The half-width of the puff decreases with increasing injection volume. Dilution, as indicated by the ratio of entrained to injected volume, was substantially smaller for the elongated puffs when compared with the spherical ones. The reduced entrained volume of elongated puffs indicates that they are less efficient in entraining ambient fluid than the spherical ones. [Preview Abstract] |
Sunday, November 20, 2005 8:13AM - 8:26AM |
AS.00002: Flow Structure of a Fully Modulated Inclined Jet in Crossflow Bertrand Dano, James Liburdy The mean and turbulent flow characteristics of a fully-modulated 45 degree streamwise inclined jet in crossflow are investigated. Results are obtained using 3D renderings of Stereo-Particle Image Velocimetry (SPIV) data for all three velocity components. The near field flow structure and the interaction with the crossflow are investigated based on ten streamwise slices of data ranging from the jet centerline spanning outward to two jet diameters. The effects of three parameters are studied: the jet Reynolds number, the pulsing frequency and the pulse duty cycle. The mean velocity ratio is defined as the mean jet exit velocity divided by the crossflow velocity, and is kept constant for all cases presented. The duty cycle is varied from 0.5 down to 0.125, such that the mean exit velocity increases in order to maintain the same average mean velocity ratio. The data are further analyzed using a vortex detection algorithm to locate the positions and strength of vortical structures in vertical streamwise plans. Results of the mean velocity field, vorticity, and Reynolds stresses, all combined with streamlines and vortex identification plots are presented. It is found that the duty cycle has a large effect on the general nature of the flow structure interaction between the jet and crossflow, which contributes to the vortex patterns identified within the flow. [Preview Abstract] |
Sunday, November 20, 2005 8:26AM - 8:39AM |
AS.00003: Three-Dimensional Vortical Structures of a Round Impinging Jet Measured by Scanning Stereo-PIV Jun Sakakibara, Toshio Hori A scanning stereo-PIV system was used to measure the 3D distribution of 3C velocity in a turbulent round jet impinged on a flat plate at normal incidence. The water jet was formed by a round nozzle with an exit diameter of $D $= 5 mm in an octagonal tank filled with water. The impingement plate was located at $x$=45$D$ distant from the nozzle exit, and the jet Reynolds number was set at $Re\approx 1000$. A laser light sheet illuminated the flow field and was scanned in the direction normal to the sheet. Two C-MOS cameras captured the particle images, and stereo-PIV method was adopted. The measurement volume ($\approx $80 $\times $ 80$\times $ 60 mm$^{3})$ containing 50 velocity planes was located around the stagnation point. Three-dimensional vortical structures were visualized by iso-surfaces of vorticity magnitude. Convection of the vortex filament in both shear layer and core of the jet were clearly observed. Production of the squared vorticity by the mean strain is quite dominant near the wall, although the turbulent strain contributes in the region away from the wall. Decomposition of the mean strain into the individual terms indicates that the radial and azimuthal straining plays a key role in amplification of the vorticity, while the mean compression in the direction noraml to the wall made a negative contribution to the production. [Preview Abstract] |
Sunday, November 20, 2005 8:39AM - 8:52AM |
AS.00004: Fluctuations properties of space averaged force in a fully turbulent jet. Benjamin Thiria, Olivier Cadot, Jean-Fran\c{c}ois Beaudoin We study the fluctuations of a global quantity in a fully turbulent flow: the drag of a disk placed in a turbulent jet, facing perpendicularly to the jet axis. The question is how are the fluctuations of the drag averaged as the size of the disk is increased? For this purpose a piezoelectric transducer is used giving measurements that are reliable until the frequency of 1Khz. The turbulence upstream the disk is characterized by mean of hot wire measurements. The velocity spectrum displays the beginning of the inertial range around 10 Hz and the dissipative scale around 1~kHz. The drag fluctuations measured over the disks can then solves fluctuations having high frequencies as small as those of the dissipative scale. For small disk diameters, the drag statistics are strongly non-gaussian with a stretched exponential tail for large values of the drag. For larger disk diameters the shape of the PDF converges through a shape that is not Gaussian. These PDF are compared to standard statiscal laws. The effect of averaging is also studied on the drag Fourier spectra.. [Preview Abstract] |
Sunday, November 20, 2005 8:52AM - 9:05AM |
AS.00005: An Experimental Study of the Far-Field of an Incompressible Swirling Jet Abolfazl Shiri, William K. George, Jonathan W. Naughton Incompressible swirling jets at different Reynolds numbers have been studied using laser Doppler anemometry method. Swirling flow produced by three pairs of symmetric injectors has been kept in the range to avoid vortex breakdown. The resulting swirling jets had a solid-body like swirl distribution at the nozzle exit. Jet growth rate and the velocity profiles have been studied at different swirl number. They have been compared to non-swirling axisymmetric jets with the same specifications. The swirl number plays an important role in that it can enhance the growth rate of the jet. The increase in growth rate starts when the swirl number reaches to a certain value (S$>$0.15). In this study, we tried to cover enough downstream distance of the jet to investigate the self-similarity of the Reynolds stresses. The predictions of the self-similar solutions theory were compared with the experiment in order to determine if the solutions describe the evolution of the flow at far field. It was found that the data from the experiments were in good agreement with the predictions from the analysis. [Preview Abstract] |
Sunday, November 20, 2005 9:05AM - 9:18AM |
AS.00006: Developing Experiment-based Dynamical Systems of the Axisymmetric Jet. Jeremy Pinier, Mark Glauser, William George With the aim of implementing closed-loop control on the flow exiting an axisymmetric jet nozzle, and to be able to capture the dynamics of the flow as it evolves downstream of the jet exit, we are developing dynamical systems based on the Navier-Stokes equations. The evolution equation is guided by a Galerkin projection of the Navier-Stokes equations onto the Proper Orthogonal Decomposition (POD) eigenfunctions. The coefficients of the ordinary differential equations for each streamwise position are then solved for using experimental data of the flow based on the moments method initially developed by the Poitiers group. A time-prediction of the evolution of the flow can then be retrieved from given initial conditions. The main experimental limitation lies in acquiring time-resolved data of the flow which is needed in the resolution of the dynamical system. The progress in the effort of training the dynamical system with time-resolved data of the jet and its implementation for control will be discussed. [Preview Abstract] |
Sunday, November 20, 2005 9:18AM - 9:31AM |
AS.00007: POD applied to stereo PIV data of the far turbulent axisymmetric jet M. W\"{a}nstr\"{o}m, W.K. George, K.-E. Meyer An experiment was performed to evaluate spatial resolution requirements for multiple and single component POD applications to cross-sections of the far axisymmetic jet. The jet of Gamard et al.\footnote{Gamard, S. et al.\ {J. Fluid Mech., 514}, pp. 205-230 (2004).} was used at an exit Reynolds number of 20,000. Three-component velocity data were obtained at downstream positions of 60, 70 and 100 diameters using stereoscopic PIV. In addition to the standard PIV processing, a novel application of the snapshot POD was used to filter the data in preparation for the classical POD analysis. The two-point Reynolds stress tensor was reconstructed from the dominant snapshot POD-modes, and the convex hull of this data set was extended using symmetry conditions. The results are believed to be relevant to not only understanding previous experiments with hot-wires, but also DNS and LES. [Preview Abstract] |
Sunday, November 20, 2005 9:31AM - 9:44AM |
AS.00008: Three-component POD of an axisymmetric wake behind a disk Murat Tutkun, Peter B.V. Johansson A comparison between the one- and three- component Proper Orthogonal Decomposition (POD) of an axisymmetric wake behind a disk is presented in this talk. The high Reynolds number axisymmetric wake behind a disk has previously been studied using one-component (streamwise) POD in a cross-section of the flow.\footnote[1]{Johansson, P.B.V. and George, W.K., {\it The far downstream evolution of the high Reynolds number axisymmetric wake behind a disk. Part 2. Slice proper orthogonal decomposition}, Journal of Fluid Mechanics, Accepted for publication, 2005.} It was found that the energetic structure of the axisymmetric wake can very efficiently be described in terms of POD modes. The POD revealed that two major features dominated the wake, one peaking at azimuthal mode-1 and at the Strouhal frequency and the other at azimuthal mode-2 and at near-zero frequency. The mode-1 peak dies off faster than the mode-2 peak, so that the far wake (x/D $\geq$50) is dominated by the latter. The aim of the present investigation is to find out if three- dimensional decomposition shows the same features as the one-dimensional. [Preview Abstract] |
Sunday, November 20, 2005 9:44AM - 9:57AM |
AS.00009: High Reynolds Number Studies in the Wake of a Submarine Model Juan Jimenez, Ryan Reynolds, Alexander Smits Results are presented from submarine wake studies conducted in Princeton University¹s High Reynolds Number Test Facility (HRTF). Compressed air is used as a working fluid enabling Reynolds numbers based on length of up to $10^8$, about 1/5 of full scale. Measurements at Reynolds numbers up to $3 \times 10^6$ have been completed, and show that, for the model condition without fins, the wake mean velocity was self-similar at locations 6 and 9 diameters downstream. Also, PIV at Reynolds numbers near $10^4$ showed that when the yaw angle was varied the sail-tip and sail-hull junction vortices increased in magnitude emphasizing the importance of fully understanding the flow characteristics of a maneuvering submarine. [Preview Abstract] |
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