Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session AB: Turbulent Shear Layers |
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Chair: Kenneth Christensen, University of Illinois Room: 101B |
Sunday, November 22, 2009 8:00AM - 8:13AM |
AB.00001: Evaluation of Similarity Theory for Weakly Swirling Jets using LDA Measurements Richard Semaan, Jonathan Naughton A similarity theory for weakly swirling jets developed by Ewing in 1999 is considered using recent experimental measurements. Momentum conserving jets with swirl numbers varying from 0 to 0.4 were measured using 3-D Laser Doppler Anemometry. This range ensured that none of the jets exhibited vortex breakdown. High quality measurements of the mean velocities and Reynolds stresses allow for a comprehensive evaluation of the theory. Despite the rapid decay of the swirl velocity relative to the axial velocity, the jet behavior is shown to be consistent with Ewing's theory even in the limited axial region where the swirl velocity is still significant. This is demonstrated through use of the experimental data to consider the constraints that are required for and the scaling quantities that result from the development of the similarity theory. The similarity theory governing weakly swirling jets is shown to hold for a range swirl numbers and thus provides another canonical flow for validating models. This theory is particularly useful for validating models that attempt to capture curvature effects. [Preview Abstract] |
Sunday, November 22, 2009 8:13AM - 8:26AM |
AB.00002: Coherent structures in uniformly sheared turbulence Christina Vanderwel, Stavros Tavoularis Uniformly sheared flow with a turbulence Reynolds number $Re_{\lambda}$ in the range from 100 to 140 has been generated in a water tunnel and its instantaneous structure has been examined using flow visualization, LDV and PIV. The flow was found to consist of regions with nearly uniform velocity and separated by relatively strong shear layers containing large vortices. The concentration of vortices and the probability distribution functions of their directions of rotation, strengths, sizes and shapes in three characteristic planes of the flow have been determined. These results, as well as high-speed scans of injected dye patterns, show that horseshoe-shaped vortices are prevalent in this flow. [Preview Abstract] |
Sunday, November 22, 2009 8:26AM - 8:39AM |
AB.00003: The Low Speed Intermittent Region of a Single Stream Shear Layer (SSSL) John Foss, Jason Peabody External intermittency: intermittent presence of vortical fluid, exists on the high and the low speed sides of a SSSL. From Corrsin and Kistler (1954) it is understood that the vortical fluid is bounded by a viscous superlayer (VSL) that is well-defined given zero vorticity in the entrained fluid. That condition is met for the SSSL flow of Morris and Foss (2003). The smoke trace from an incense stick provides a convenient technique to mark the 3-D locations of the VSL. Specifically, the vorticity at the VSL ``shreds'' the end of the trace; the shredding is captured by two cameras with calibrated x-y=f(z) and y-z=g(x) image planes. Complementary transverse vorticity measurements were acquired in the spatial domain indicated by the ``shredding.'' Interpreted results will be presented. Corrsin, S. and Kistler, A.L. (1954) ``The Free Stream Boundaries of Turbulent Flows,'' NACA TN 3133. Morris, S.C. and Foss, J.F. (2003) ``Turbulent boundary layer to single-stream shear layer: the transition region'', Jour. Fluid Mechanics, 494, pp. 187-221. [Preview Abstract] |
Sunday, November 22, 2009 8:39AM - 8:52AM |
AB.00004: An Experimental Study of Circular and Rectangular Heated Jets in Cross-Flow B.E. Johnson, G. Elliott, K.T. Christensen Heated plumes of fluid emanating from both flush and raised stacks occur in a wide variety of technologically-relevant applications and the dispersion of this heated, and sometimes contaminated, fluid is therefore of practical concern. To this end, a detailed series of experiments are under way to document the downstream development of heated jets of both circular and rectangular cross-section emanating into a cross-flow with the intent of constructing an experimental database for validation of on-going large-eddy simulations. Multiple cross-stream velocities as well as various jet exit velocities and temperatures are under study to understand the plume development both in the near- and far-field. The jet flow is driven by a high-pressure regenerative blower and heated with an open-coil heater while the cross-flow is provided by an open circuit wind tunnel. Mean temperature fields and streamwise velocity fields are measured using a rake of Pitot-static probes and thermocouples at select locations downstream of the jet. Of particular interest, the impact of jet exit temperature, velocity and cross-section on the downstream development of the heated plume is explored. Similarities and differences between flush and raised stack configurations under identical experimental conditions will also be highlighted. [Preview Abstract] |
Sunday, November 22, 2009 8:52AM - 9:05AM |
AB.00005: Open Loop Forced Experimental Investigation of Optical Beam Propagation through a Free Shear Layer Casey Fagley, Stefan Siegel, Jurgen Seidel, Thomas McLaughlin The performance of airborne platforms emitting or receiving light beams is severely hampered by the flow field around the turret mounted on the air vehicle. From a fluid dynamics point of view, the flow separating from the turret develops large, coherent structures. From an optical point of view, these structures due to their associated density variations, cause large optical distortions since the index of refraction is a function of density. The goal of this research is to reduce optical distortions by mitigating these structures using feedback flow control. A blowing and suction slot along the top of the backwards facing step allows for actuation of the flow field. A study varying open loop forcing frequency and amplitude of the actuation signal shows the influence on the natural shedding frequency responsible for the large coherent structures. Initial findings support that forcing with more than twice the natural frequency does not produce structures that increase the optical path difference (OPD), measured by a Malley probe, while hot film measurements show that structures at the forcing frequency are present. The differences between these OPD and hot film measurements will be demonstrated and supported with simulation results. [Preview Abstract] |
Sunday, November 22, 2009 9:05AM - 9:18AM |
AB.00006: Spectral analysis of ``homogenized'' PIV data of axisymmetric jet turbulence Maja W\"{a}nstr\"{o}m, William K. George, Knud Erik Meyer This paper concerns the estimation of one-dimensional spatial spectra from a set of 10,580 two-component velocity fields in a plane cut along the centerline axis of a turbulent air jet. The jet nozzle diameter $d =1cm$ and the field-of-view extends from $30d$ to $100d$ and covers at least four jet half-widths. The Reynolds number based on nozzle diameter is $Re = 20, 000$. Following [1], PIV data of the growing flow was mapped and re-sampled into streamwise homogeneous similarity coordinates, $\eta =r/\delta_{1/2}(x)$ and $\xi = \ln[(x-x_o)/D]$. Inevitable spatial variation in attainable dynamic range was overcome by the extensive number of statistically independent samples. Studies of the effects of window length and type, filtering, sampling noise and data re-sampling on the spectral energy distribution are performed and discussed. Finally, the spectral estimates are compared to the temporal estimates of [2], which are obtained by hotwire using Taylor's Hypothesis.\\[4pt] [1] Ewing, D. et al.\ J. Fluid Mech., 577, 309-330, 2007.\\[0pt] [2] Frohnapfel, B. Multi-Point Similarity of the Axisymmetric Turbulent Far Jet and Its Implication for the POD. Master Thesis, U. Erlangen 2003. [Preview Abstract] |
Sunday, November 22, 2009 9:18AM - 9:31AM |
AB.00007: ABSTRACT WITHDRAWN |
Sunday, November 22, 2009 9:31AM - 9:44AM |
AB.00008: Measurements in a High Reynolds Number Wake Juan Jimenez, Marcus Hultmark, Alexander Smits Experiments were conducted in the Princeton/ONR HRTF windtunnel with air pressurized up to 220atm. The wake of a DARPA SUBOFF submarine model was measured at 5 different downstream locations for Reynolds numbers from $1\times 10^6$ to $70\times 10^6$. For all Reynolds numbers studied, the mean velocity distribution is self-similar from 3 diameters, $D$, downstream for the side where the support is not located. In contrast, self-similarity in the Reynolds stresses is not reached at the furthest downstream location ($x/D=15$). The non-dimensional fluctuations are Reynolds number dependent for all measured Reynolds numbers. The energy spectra reveal two peaks in the near-wake. The lower wavenumber peak corresponds to a Strouhal number based on diameter and freestream velocity of about 0.2, suggesting that it is associated with an azimuthal or helical shedding mode in the wake. The peak decays with downstream distance, suggesting that this mode might play a parital role in the approach to self-similarity of the turbulent stresses [Preview Abstract] |
Sunday, November 22, 2009 9:44AM - 9:57AM |
AB.00009: Flow Field of Three-Dimensional Turbulent Wall Jets Mark Tachie, Martin Agelin-chaab A wall jet is formed when a jet of fluid is directed tangentially along a wall. Wall jets can be two- or three-dimensional. Three-dimensional wall jets (3DWJs) are complex flows whose structures are still not well understood despite the extensive studies on this subject. For example, the mechanism responsible for their more rapid lateral spread rate than in the wall-normal spread rate is not well understood. Velocity measurements of 3DWJs were conducted using particle image velocimetry. The 3DWJs were formed by jets exiting a $d$ = 7 mm inside diameter circular pipe (143$d$ in length) placed to flush the test section floor. The Reynolds numbers based on the jet exit velocities and jet exit diameters were 5000, 10000 and 20000. The detailed flow fields of the 3DWJs were examined in terms of mean velocities and one-point turbulence statistics. In view of the wide range of length and temporal scales that are present in turbulent flows, multi-point turbulence statistics such as two-point velocity correlations and proper orthogonal decomposition are used to document the salient features of the 3DWJs. [Preview Abstract] |
Sunday, November 22, 2009 9:57AM - 10:10AM |
AB.00010: Structure of three-dimensional turbulent offset jets with small offset distances Martin Agelin-chaab, Mark Tachie An offset jet is a jet that discharges into a medium above a wall which is offset by a certain distance. The ``Coanda effect'' forces the offset jet to deflect towards the wall and eventually attaches itself to the wall. The only detailed study of three-dimensional offset jets (3DOJs) did not report the flow field in the region from the jet exit to the point where the jet attaches itself to the wall. In this region flow reversal is expected. Velocity measurements of 3DOJs were conducted using particle image velocimetry. The 3DOJs have different jet exit offset distances ($h)$ normalized by the jet exit diameter ($d)$ of $h$/$d$ = 0.5 to 4. The Reynolds numbers based on the jet exit velocities and jet exit diameters were 5000, 10000 and 20000. The detailed flow fields of the 3DOJs were examined in terms of mean velocities, and one-point turbulence statistics. In view of the wide range of length and temporal scales that are present in turbulent flows, multi-point turbulence statistics such as two-point velocity correlations and proper orthogonal decomposition are used to document the salient features of 3DOJs. [Preview Abstract] |
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