Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session OK: Free Surface Flows III |
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Chair: Dmitry Kopelevich, University of Florida Room: Tampa Marriott Waterside Hotel and Marina Meeting Room 4 |
Tuesday, November 21, 2006 12:15PM - 12:28PM |
OK.00001: Hydraulic jumps in one dimension Tomas Bohr, Anders Andersen, Daniel Bonn, Farid Bouramrirene We present a study of hydraulic jumps in thin fluid layers with flow predominantly in one direction, created either by confining the flow to a narrow channel or by providing an inflow in the form of a narrow sheet. In all cases we find that the (normal) velocity of the flow at the low side of the jump has a particular critical value, larger than the wave speed. In the channel flow we clearly demonstrate the linear height profile predicted by Watson (1964), although turbulent fluctuations change the apparent viscosity. We show how to calculate the flow structure through the jump, where separation occurs. In the sheet case we find that the jump has the shape of a lozenge with sharply defined, oblique shocks. The variation of the angle of the lozenge with flux is determined by the condition that the normal velocity at the jump remains at the critical value. [Preview Abstract] |
Tuesday, November 21, 2006 12:28PM - 12:41PM |
OK.00002: Steady two-layer flow in a topographically patterned channel Richard D. Lenz, Satish Kumar The steady behavior of the interface between two liquid layers flowing in a channel with one flat wall and one exhibiting a step-change in surface topography is considered. A 1D model based on the lubrication approximation is used to describe the interfacial shape. This shape is determined in part by the nature of the topographic variations encountered, but influenced strongly by the driving forces for flow and the liquid layer thickness and viscosity ratios. Interfacial behavior is characterized over a range of problem parameters and connected to the properties of simpler single-phase flows. Variations in the capillary length scale are explained through a scaling analysis, and the use of repulsive van der Waals forces to suppress interfacial features is explored. The results are of relevance to several current technological applications including microfluidics, multilayer coating, and lithographic printing. [Preview Abstract] |
Tuesday, November 21, 2006 12:41PM - 12:54PM |
OK.00003: Linear stability theory of sheared menisci in thin channels Burt Tilley, Ferdinand Hendriks, John Billingham, Christopher Raymond, Joseph Fehribach, Paul Dellar Fluid dynamic bearings (FDB) are rapidly replacing ball bearings for spindles of hard disk drives. Capillary effects are used to keep the lubricant (oil) in the FDB, while viscous effects produce the lubrication pressures needed for contact-free suspension of the rotor in the spindle. We analyse this system in the thin-gap limit, which results in a Couette flow along the flat oil-air interface. A linear stability analysis is performed in the limit of vanishing Reynolds number but where contact-line effects are pertinent. In this limit, two modes are found which are neutrally stable and are independent of the wavenumber of the azimuthally varying disturbance. Extensions from the zero-Reynolds-number limit will also be discussed. [Preview Abstract] |
Tuesday, November 21, 2006 12:54PM - 1:07PM |
OK.00004: The effect of downstream location on the statistics of the surface temperature field for flow over an air/water interface K. Peter Judd, J.R. Saylor Experiments were carried out in a wind/water tunnel with a wind speed sufficiently small that both free and forced convection occurred. Infrared (IR) imagery was used to characterize the surface temperature field of the water as it transferred heat to the overlaying air. The root mean square (rms) of the surface temperature was computed from the IR images that extended over a fixed footprint on the interface. The IR imagery was broken into segments. The rms computed from each segment was found to vary from segment-to-segment along the streamwise direction. This variation in rms with downstream position is reported for a range of heat fluxes and wind speeds. The effect of segment size on the rms versus heat flux behavior is also discussed. [Preview Abstract] |
Tuesday, November 21, 2006 1:07PM - 1:20PM |
OK.00005: The effect of wind speed on the statistics of the temperature field of an air/water interface J.R. Saylor, T.A. Conover An experimental study is presented of the transfer of heat from a warm body of water to an air flow above it. This work was conducted in a wind/water tunnel, permitting these experiments to be conducted over a range of wind speeds and heat fluxes. The temperature field of the air/water interface was measured using an infrared camera. These temperature fields were used to compute the root mean square (rms) of the interfacial temperature. The relationship between the rms and the heat flux was obtained, and the sensitivity of this relationship to the wind speed was determined. The experiments were conducted for conditions where forced convection and natural convection both contribute to the heat transfer rate. Data are presented for cases where the water surface was covered with a soluble and an insoluble surfactant monolayer. Sample infrared images are presented for several wind speeds, and the relevance of this work to the remote sensing of heat flux will be discussed. [Preview Abstract] |
Tuesday, November 21, 2006 1:20PM - 1:33PM |
OK.00006: Theoretical Analysis of Critical Marangoni Number for Oscillatory Flows with High Prandtl Number Fluids Shinichi Yoda, Satoshi Matsumoto, Atsuki Komiya Many experiments to determine the critical Marangoni number at the onset of oscillatory flows for high Prandtl number (\textit{Pr}) fluids have showed a dependence of a characteristic length such as the diameter of the liquid column. This fact contradicts the similarity principle in fluid physics. This paper investigates the reasons why the critical Marangoni number has shown such a dependency by considering the difference in temperature distribution on the free surface that is caused by a difference in \textit{Pr}. higher \textit{Pr} fluids form a thermal boundary layer with a steep temperature gradient in the vicinity of both the hot and cold parts for Marangoni convection experiments, although the middle of the free surface between the hot and cold disks has no temperature gradients. This feature was obtained by two-dimensional simulations with container shape Marangoni experiments. By considering the partial temperature distribution on the free surface, a basic model for the understanding of Marangoni number for higher\textit{ Pr} fluids is proposed by introducing a dimensionless parameter, the effective Marangoni number. The most exact experimental results obtained from microgravity experiments were used to evaluate the effective Marangoni number which is not dependent on the characteristic length dependence at the onset of oscillatory flows. This parameter is consistent with the similarity principle in Marangoni convection behavior. [Preview Abstract] |
Tuesday, November 21, 2006 1:33PM - 1:46PM |
OK.00007: Measurement of the Bubbles Entrained in a Translating Axisymmetric Plunging Laminar Jet M. Tavakolinejad, M. Shakeri, P. Chang, J.H. Duncan Air entrainment induced by a translating axisymmetric laminar vertical water jet as it impinges onto the free surface of a quiescent pool of water is studied experimentally. The experiments are performed in a towing tank that is 24 ft long, 2.5 ft wide and 3 ft deep. When the jet is stationary, the water surface around the jet impact site is smooth and no air is entrained. When the jet is moving horizontally, a depression of the free surface forms directly downstream of the jet. Air is entrained from the cusp formed at the bottom of the leading edge of the depression. Previously presented high-speed flow visualization movies of the entrainment process have show that the bubbles enter the water when vortices from the jet shear layer pass over the cusp and that these bubbles are initially trapped within the vortices. Further downstream, two regions of bubbles are formed. Close behind the jet and near the free surface there is a region of large irregular shaped bubbles with relatively high rise velocity. Deeper in the water and extending further downstream there is a region of small diameter bubbles with lower rise velocity. The results of shadowgraph measurements of the size distributions of the small bubbles in fresh and salt water are presented. In the presence of salt water, a larger number of small diameter bubbles is found. [Preview Abstract] |
Tuesday, November 21, 2006 1:46PM - 1:59PM |
OK.00008: Liquid Vortex Fluid Dynamics for Fusion Energy Applications Philippe Bardet, Omer Savas A turbulent annular swirling liquid contiguous wall jet is characterized experimentally in a ``vortex tube.'' The flow is proposed for use in a thick liquid first-wall chamber concept for inertial fusion power plants. The three components of planar velocity vector fields are measured with a single camera split-screen stereoscopic particle image velocimetry scheme. The combined use of fluorescent particles and cut-off filters effectively blocks glare reflected from the liquid-air interface. Flow field measurements in the vicinity of a free surface are thus successfully obtained in the presence of strong surface deformations. The jet is studied for Reynolds numbers ranging from 3,200 to 14,000 and between 1.5 and 11 ``vortex tube'' diameters downstream of the injection nozzle. Between 1.5 and 8 diameters, the average azimuthal velocity profile alone is non uniform away from the wall. Large vortical structures are consistently observed. Their wavelength increases with the distance from the nozzle. The turbulent kinetic energy decreases slowly with distance while the dissipation decreases rapidly. At 11 diameters, the wall effect influences strongly the average velocity profiles. The vortical structures disappear and the turbulent kinetic energy increases. [Preview Abstract] |
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