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 H15: Free-Surface Flows II |
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Chair: Vladimir Ajaev, Southern Methodist University Room: 318 |
Monday, November 21, 2011 10:30AM - 10:43AM |
H15.00001: A surface PIV approach for the remote monitoring of mean and turbulent flow properties in an open channel Erika Johnson, Edwin Cowen In an effort to develop a reliable, continuous and efficient method of remotely monitoring bathymetry, water column turbulence levels and mean velocities, a surface PIV (particle image velocimetry) experiment is conducted in a wide open channel ($B/h > 12$) for a range of flow depths. Mean velocity, turbulence intensities, dissipation, divergence, vorticity as well as integral length scale statistics have been calculated from the surface PIV data. The results reveal the presence of secondary flow within the channel, which leads to heterogeneous turbulence metrics on the surface; for example, the streamwise turbulent intensities and dissipation vary strongly as a result of the secondary motion. The integral length scales vary predictably with the flow depth ($L~\approx~ 0.3h$) and a correlation between the surface dissipation and dissipation in the water column allows estimates of the bed shear stress. These findings have important implications for developing new technologies for stream gauging, near shore and estuarine monitoring. [Preview Abstract] |
Monday, November 21, 2011 10:43AM - 10:56AM |
H15.00002: Statistical study of scalar transport in wind-driven free-surface turbulent flows Hamid Reza Khakpour, Lian Shen, Takeru Igusa We examine statistical methods for the study of the correlation between characteristic turbulence structures and scalar transport process in free-surface turbulence. We perform direct numerical simulation for the advection and diffusion of passive scalars in wind-driven free-surface turbulent shear flows. Using conditional averaging of events with strong scalar surface flux or large vorticity components, we characterize the correlation of surface flux with a variety of subsurface vortical structures. We then present a clustering method based on the Expectation-Maximization (EM) Algorithm. This clustering method is found to be effective in identifying dominant flow patterns which are associated with characteristic vortical structures. The method also provides insights into the induction of upwelling by vortical structures which, in turn, greatly enhances the scalar surface flux. The clustering method is general and can also be used for applications beyond interfacial scalar transport. [Preview Abstract] |
Monday, November 21, 2011 10:56AM - 11:09AM |
H15.00003: The thermal and hydrodynamic structure of a turbulent buoyant jet on clean and contaminated free-surfaces K. Peter Judd, Ivan Savelyev, Geoffrey Smith The thermal and hydrodynamic structure of a turbulent buoyant jet impinging normal to clean and contaminated free-surfaces was examined experimentally for fixed jet depth, reduced gravity and several Reynolds numbers. The objective of this investigation is to describe the resulting interaction and morphology of the surface thermal structures. Fluid for the jet is supplied from a gravity feed whose ambient temperature is several degrees above the receiving fluid of a large water basin. Thus the warmer fluid serves as a passive marker. The spatial and temporal characteristics of the surface thermal field were mapped using a mid-wave infrared imager sensitive to radiation in the 3-5 micron band and with an NEDT of 25 mK. As the Reynolds number and/or the degree of contamination are changed, noticeable structural changes were observed in the thermal field around the core and the outer turbulent/non- turbulent regions. Additionally, the subsurface jet was simultaneously interrogated using DPIV and the surface thermal structures are discussed in light of the resulting characteristics of the flow field. [Preview Abstract] |
Monday, November 21, 2011 11:09AM - 11:22AM |
H15.00004: Large Eddy Simulation of Free-Surface Flow past a Submerged Submarine Fairwater at Moderate Reynolds Number Zaheer Ikram, Eldad Avital, John Williams The affects of reducing submergence depth around a submerged submarine fairwater without its associated appendages is numerically studied using Large Eddy Simulation. The submerged body is modelled using a immersed boundary method, whilst the free-surface is accounted for using a moving mesh. The numerical simulations are performed at a Reynolds number of 8$\times $10$^{4}$ for a submergence ratio in the range of 0.44-0.32 and for Froude numbers $<$ 1. Both the statistical and structural behaviour of the flow are examined. Statistically, time averaged velocity profiles, turbulence intensities, kinetic energy spectra and budgets have shown that the major part of the turbulence is confined to the near wake region of the fairwater. Structurally, no vortices are found to show significant rise or interaction with the free-surface, whilst in the wake vortices are found to be present for over 50{\%} of the total monitored period. Reducing the submergence depth is found to influence the tip vortex. In all cases, the surface waves generated by the submerged fairwater are of a Kelvin kind. [Preview Abstract] |
Monday, November 21, 2011 11:22AM - 11:35AM |
H15.00005: Harnessing sloshing as a passive dampener Taylor Killian, Robert Klaus, Tadd Truscott This study investigates the impact dynamics of hollow elastic spheres partially filled with fluid, similar to roller hockey balls. Unlike an empty elastic ball, the fluid mitigates some of the rebound through an impulse driven exchange of energy wherein the fluid is forced into a jet inside the ball. Images gathered through experimentation show that the fluid reacts more quickly to the impact than the ball, which decouples the two masses (fluid and ball), imparts energy to the fluid, and removes rebound energy from the ball. The experimental results are compared to an energy method where energy is transferred from the external motion of the ball, to the internal flow of the fluid. Results suggest that while the internal liquid affects the fluid motion, the rebound characteristics of the ball are uniform for a given amount of fluid. Implications of this work on an analog to the roller hockey ball is a potential use of similar passive dampening systems in sports technology and marine engineering. [Preview Abstract] |
Monday, November 21, 2011 11:35AM - 11:48AM |
H15.00006: Experimental investigation of turbulent wall jet Matthieu A. Andre, Philippe M. Bardet Water jet flowing on a flat plate surrounded by quiescent air constitutes a standard case for the study of the interaction between turbulence and the liquid-air interface. This is of particular interest in the understanding of heat and mass transfers across interfaces. The structure of the surface has a great influence on the rate of the transfers which is critical for chemical processes like separation or absorption; pool-type nuclear reactor; climate modeling etc. This study focuses on high Froude (8 to 12) and Weber (3300 to 7400) numbers at which the surface exhibits small wavelength and large amplitude deformations, such as ligaments, surface break up with air entrainment and droplets projection. The experiment features a high velocity (up to 7.5 m/s) water wall jet (19.05mm thick at the nozzle exit) flowing on a flat plate ($Re=10^5$ to $1.5\cdot 10^5$). High speed movies and PLIF visualization show the evolution of the surface from smooth to 2D structures, then 3D disturbances as the turbulence arising from the wall interacts with the surface. [Preview Abstract] |
Monday, November 21, 2011 11:48AM - 12:01PM |
H15.00007: Free surface shape and flows of an inviscid liquid Laust Toph{\O}j, Tomas Bohr When the Euler equations governing inviscid flow are projected onto a stationary free surface, one can obtain a self-contained set of equations involving only the values of the physical fields on the free surface. These can be solved to yield relations between the shape of the free surface and the surface-tangential flow components at the free surface. Applications of a simplified set for systems with circular symmetry include [Bergmann et. al., JFM 679, pp. 415-431 (2011)]. The talk will focus on the derivation of these surface flow equations, with the free surface treated as a Riemann manifold. Examples of applications will be discussed. [Preview Abstract] |
Monday, November 21, 2011 12:01PM - 12:14PM |
H15.00008: ``Oenodynamic'': hydrodynamic of wine swirling Martino Reclari, Matthieu Dreyer, Stephanie Tissot, Danail Obreschkow, Florian Wurm, Mohamed Farhat A crucial step in wine tasting is the so called ``swirling,'' necessary to release the bouquet of the wine: a gentle circular movement of the glass generates a wave propagating along the glass walls, enhancing oxygenation and mixing. Although being used in a large variety of other applications (e.g. cells cultures in orbital shaken bioreactors) this motion is not yet well understood. Using a simplified model we experimentally investigated the shape of the free surface and the mixing, and we identified a group of dimensionless parameters governing the flow. [Preview Abstract] |
Monday, November 21, 2011 12:14PM - 12:27PM |
H15.00009: Standing ripple rings within the super-critical flow region of a circular hydraulic jump Xiyu Du, Paul Stanley The circular hydraulic jump in the presence of a soluble surfactant can display a stable, narrow ring of static ripple features within the inner super-critical flow region. These ripples are likely capillary surface waves pushed inward from the region of the hydraulic jump by surface tension gradient Marangoni type stresses. The behavior appears to be similar to that of the fluid pipe observed when a stream of pure water strikes a reservoir contaminated by a surfactant. In this experiment we primarily consider soluble surfactant dissolved in the source for the impinging jet, so that jet and downstream fluid have same surfactant concentration. We examine the effects of the surfactant concentration on the behavior of the jump and the inner static ripple feature, and propose a model as to the cause and location of these static ripples. [Preview Abstract] |
Monday, November 21, 2011 12:27PM - 12:40PM |
H15.00010: Shallow flow down a spiral channel of small torsion and rectangular cross section Yvonne Stokes, Hayden Tronnolone, Stephen Wilson, Brian Duffy Motivated by a desire to understand better the operation of spiral gravity separators, we consider flow of small depth down a helically wound channel of small torsion and rectangular cross section. The small fluid depth makes experimental investigation difficult, so that mathematical modelling and theoretical and computational studies are of great value for determining how such flows are influenced by fluid properties and geometrical parameters. We present a thin-film model, comprised of a system of non-linear ordinary differential equations, and show that there is a limiting value of a dimensionless parameter, defined in terms of fluid properties and geometrical parameters, beyond which there is no physically meaningful solution. Thin-film model solutions are compared with numerical solutions of a PDE model that does not assume small fluid depth. [Preview Abstract] |
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