Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session R10: General Fluid Dynamics III |
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Chair: Jeremy Marston, King Abdullah University of Science and Technology Room: 313 |
Tuesday, November 22, 2011 12:50PM - 1:03PM |
R10.00001: An Investigation of Length Scales in Active Grid Generated Turbulence R. Jason Hearst, Philippe Lavoie A novel active grid design is used to generate high Reynolds number homogeneous, isotropic turbulence. Typically, active grids consist of square wings mounted on a bi- planar mesh of rods. Each rod of the mesh is controlled independently by a stepper motor, which receives randomly varied signals defining its period and speed of rotation. The present design consists of two bi-planar rod meshes. Wing placement alternates between the forward and aft meshes, allowing for the motion of adjacent wings to be decoupled by mounting them on independently rotating rods. By changing the degree of correlation between the motion of wings, the length scales of the output turbulence may be influenced while the turbulence itself remains approximately homogeneous and isotropic. Furthermore, the structure of the turbulence may be dependent on the wing geometry. As such, alternative wing geometries (e.g. circular) are also investigated. The primary focus of this study is to investigate the effect of initial conditions on the length scales of turbulence in the context of active grid generated turbulence. [Preview Abstract] |
Tuesday, November 22, 2011 1:03PM - 1:16PM |
R10.00002: Identification and manipulation of dynamic modes in nematic liquid crystals Zrinka Greguric Ferencek, Tyrus Berry, Timothy Sauer, John Robert Cressman We present work identifying and manipulating patterns formed in an electroconvecting nematic liquid crystal. The existence of coherent, temporally and spatially correlated, structures are found in a wide range of driven systems. The development of new experimental and analytical techniques has enabled the identification of these structures and is beginning to elucidate their role in establishing macroscopic behavior. Here we describe an algorithm used to identify and track these structures, and report on the effects of local and global stimulation on their creation and evolution. [Preview Abstract] |
Tuesday, November 22, 2011 1:16PM - 1:29PM |
R10.00003: Power consumption and dynamic structure in electroconvecting liquid crystals John Cressman, Zrinka Greguric Ferencek, Tyrus Berry, Timothy Sauer A wide range of driven systems display complex, but correlated, dynamics as well as large fluctuations in energy injection, storage, and dissipation. We use an electroconvecting nematic liquid crystal as a model system to investigate the relationship between dynamical structure and energy flow. We use a dimensionality-reduction algorithm to identify the creation, evolution and annihilation of patterns of defects in a weakly-driven electroconvective state. By simultaneously measuring the electrical power drawn by the sample we are able to determine correlations between energy injection and defect dynamics. We will discuss these correlations as well as the interplay between energy flow and dynamic structures in this system. [Preview Abstract] |
Tuesday, November 22, 2011 1:29PM - 1:42PM |
R10.00004: Hot balls splash and sink fast Jeremy Marston, Ivan Vakarelski, Sigurdur Thoroddsen, Derek Chan When a heated sphere is immersed in a liquid, we induce an inverted Leidenfrost effect whereby the sphere is wrapped in a vapour jacket which protects it from physical contact with the liquid and, when released to fall freely in the liquid, the sphere's terminal velocity can increase dramatically compared to a cold ball. This Leidenfrost-induced vapour layer can lead to significant drag reduction by up to 85\% which appears to be the limiting case for drag reduction techniques based on gas layer injection. In a related experiment, when the heated sphere is released from above the surface, the dynamics of the entry are significantly different from the cold case, resulting in a prompt splash and cavity formation. We propose that this experiment is the ultimate non-wetting scenario during water-entry problems. [Preview Abstract] |
Tuesday, November 22, 2011 1:42PM - 1:55PM |
R10.00005: Spatial characterization of underwater turbine wakes using Three-dimensional three-component (3D3C) velocity measurements Seung-Jae Lee, Leonardo Chamorro, Dan Troolin, Roger Arndt, Fotis Sotiropoulos A growing interest in underwater turbines (using tidal, river, and marine currents among others) has been observed during the last few years. A fundamental understanding of the turbulent flow around underwater turbines is crucial to predicting the potential effects of these structures on the local morphology, water flow, and power available in the current. The flow structure downstream of a turbine are inherently complex in that it is both unsteady and three dimensional. For this reason, a measurement technique that captures the full volumetric three-dimensional velocity field is advantageous for analyzing the complexity of the flow. In this study, a miniature horizontal axis 3-blade underwater turbine, aligned in the direction of the mean flow, was placed in a water flume at the St. Anthony Falls Laboratory at the University of Minnesota. Three-dimensional three-component (3D3C) velocity measurements were made in the flow downstream of the miniature underwater turbine. Wake evolution, turbulence characteristics and primary three-dimensional flow features were identified in the instantaneous and ensemble-averaged flows at different locations downstream of the turbine. [Preview Abstract] |
Tuesday, November 22, 2011 1:55PM - 2:08PM |
R10.00006: Physics of badminton shuttlecock. Part 2 : Turn around Baptiste Darbois Texier, Caroline Cohen, David Que Re, Christophe Clanet We study experimentally shuttlecocks dynamics. In this part we show how the shuttlecock shape is optimized for badminton play. The shuttlecock always flies the nose forehead. After the impact it has thus to return. Actually it returns, oscillates and then stabilizes. We try to understand these damping oscillations and draw an analogy with the dandelions achenes and parachutists. [Preview Abstract] |
Tuesday, November 22, 2011 2:08PM - 2:21PM |
R10.00007: Laminar jet injection in a pipe with co-flow Jaime Schmieg, Mark Stremler, Pavlos Vlachos Particle Tracking Velocimetry (PTV) was used to investigate confined injection from a generic end-hole catheter within an axial co-flow environment. PTV was carried out in an iterative fashion where an approximate field was calculated from several time instances, and subsequently used as an estimator for hybrid tracking. The influence of momentum ratio on jet expansion, transport, and flow patterns was studied for several velocity ratios (VR = V$_{jet}$/V$_{out})$ between 0 and 10. The Reynolds number of the outer flow was 150 and that of the inner flow varied from 0 to 260. Flow patterns behind the catheter were dependent upon VR with recirculation regions present for low ratios. A separation bubble was observed behind the catheter for velocity ratios below 0.5 and two counter-rotating vortices were seen for VR = 0. As VR increased, asymmetry in the outer flow resulted in a single vortex behind the catheter with its position skewed toward the low flow side of the vessel and larger entrainment was present on the high flow side of the vessel. As VR increased above 0.5, recirculation was not observed and at VR = 1.0 the jet velocities were mainly in the streamwise direction. [Preview Abstract] |
Tuesday, November 22, 2011 2:21PM - 2:34PM |
R10.00008: Effects of Exhaust Gas Recirculation on SI Engines at Wide Open Throttle Sydney Bronson, Paulius Puzinauskas Exhaust gas recirculation, a charge dilution technique, has proven to be an effective method of reducing NOx emissions and fuel consumption of spark ignition engines. Wide open throttle operation also increases overall engine efficiency by reducing the pumping losses caused by throttling. In this study, the emissions and fuel economy benefits of exhaust gas recirculation (EGR) at wide open throttle conditions were quantified using a 2.4L port-injected engine. Engine performance and emissions data were recorded as the percentage of EGR in the intake charge was increased from zero to just above thirty percent (the EGR limit). This EGR percentage, in-cylinder pressure measurements, and the temperatures and pressures of the intake and exhaust were all recorded to ensure stable operating conditions. These tests were performed with a stoichiometric air-fuel ratio at a constant speed of 2000 rpm at wide open throttle. The variation of brake specific fuel consumption and emissions (in particular NOx) with increasing EGR percentages was analyzed. [Preview Abstract] |
Tuesday, November 22, 2011 2:34PM - 2:47PM |
R10.00009: Pressure-velocity correlations in a flow upstream of a forward-facing step David Pearson, Paul Goulart, Bharathram Ganapathisubramani The 2-dimensional velocity field upstream of a forward step was determined
experimentally using Particle Image Velocimetry. A total of 4 seconds of data was
acquired at $8000\rm{Hz}$. The flow velocity was $10\rm{ms^{-1}}$ with an
$\rm{Re}_h$ of 20000, where $h=0.03\rm{m}$ is the step height. The boundary layer
thickness relative to step height was $\delta/h=1.6$. The upstream surface pressure
fluctuations were simultaneously measured using an array of 9 microphones embedded
in tunnel floor. These pressure fluctuations are shown to have a direct linear correlation
to the velocity perturbations. The correlation has a maximum of approximately 0.3 at
upstream stations $x/h>2$ and reduces toward background noise levels as the flow
approaches separation at $0.5 |
Tuesday, November 22, 2011 2:47PM - 3:00PM |
R10.00010: ABSTRACT WITHDRAWN |
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