Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session R7: Multiphase Flows IX |
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Chair: Casey Harwood, University of Michigan Room: 329 |
Tuesday, November 26, 2013 1:05PM - 1:18PM |
R7.00001: Experimental Investigation of Ventilation of a Surface Piercing Hydrofoil Casey Harwood, Francisco Miguel Montero, Yin Lu Young, Steven Ceccio Bodies that pierce a liquid free-surface are prone to entrainment of atmospheric and/or vaporous gases. This process, called ventilation, can occur suddenly and violently, drastically altering hydrodynamic response. Experiments have been conducted at the free-surface towing-tank in the University of Michigan Marine Hydrodynamics Laboratory to investigate fully attached, partially ventilated, and fully ventilated flows around a canonical surface-piercing hydrofoil. The objectives of the work are: (i) to gain a broad and improved understanding of the physics of ventilation, (ii) to classify the physical mechanisms by which ventilation inception and washout may occur and quantify the conditions required for each mechanism and (iii) to quantify the effects of ventilation on global hydrodynamic responses, including the six force and moment components. Experimental data and high-speed video will be used to illustrate the impact of ventilation on hydrodynamic loads, pressures, and flow structures. The completion of this study is expected to contribute significantly toward a comprehensive understanding of ventilation physics, and toward an improved ability to design safe and controllable ventilated lifting surfaces for use in propulsion, energy harvesting, and turbomachinery. [Preview Abstract] |
Tuesday, November 26, 2013 1:18PM - 1:31PM |
R7.00002: Influence of scaling effects in the ventilation of surface-piercing bodies Francisco Miguel Montero, Casey M. Harwood, Yin Lu Young, Steven L. Ceccio Ventilation is a process by which atmospheric air is entrained to the submerged portion of a body. The study of this process is of critical importance to the design and control of surface piercing bodies, such as hydrofoils, propellers, struts and turbines, as it can result in a very sudden variation of the forces acting on the body. Ventilation is also influenced by the presence of vaporous cavitation. This cavitation-ventilation process can be complex, and in order to replicate it experimentally, there are several scaling issues that must be carefully considered. The objectives of this work are: (1) to characterize the different ventilation mechanisms, the various parameters that influence the ventilation process, as well as the resultant impact on performance, (2) to discuss and quantify scaling effects in model tests in towing tank and cavitation tunnel studies, and (3) to discuss additional research needs in terms of experimental and numerical modeling. Theoretical arguments, as well as prior and new experimental data, will be used to present the different ventilation mechanisms and derive and illustrate the related scaling issues in both cavitation tunnel and towing tank studies. [Preview Abstract] |
Tuesday, November 26, 2013 1:31PM - 1:44PM |
R7.00003: Forced drainage in a 2D foam in a microfluidic system using thermocapillary stress Marie-caroline Jullien, Vincent Miralles, Bertrand Selva, Julien Marchalot, Isabelle Cantat We present an experimental configuration allowing the possibility to control the liquid fraction in a 2D microfoam located in a Hele-Shaw cell. A Marangoni stress at the air-water interface is generated by applying a constant temperature gradient in situ, and leads to the drainage of the liquid phase. First, in order to avoid gravity drainage, the cell is placed horizontally and we are able to drain up to 70$\%$ of the liquid phase, for foams of initial liquid fraction $\phi_0 \sim 15 \%$. Next, the cell is placed vertically and the Marangoni stress for temperature gradients above 3.1K.mm$^{-1}$ is strong enough to counterbalance gravity drainage. Finally, a mass conservation approach based on scaling arguments and numerical simulations giving access to the velocity profile in a pseudo-Plateau border happen to be in very good agreement with the experimental results, showing that we can accurately control the liquid fraction in a 2D microfoam. [Preview Abstract] |
Tuesday, November 26, 2013 1:44PM - 1:57PM |
R7.00004: COST Action FP1005 ``Fibre suspension flow modelling'' Cristian Marchioli Fibre suspensions are extremely complex solid-liquid systems since their components (fibres, flocs, air bubbles and additives) interact mutually in a complex way. The dynamics of fibre suspensions are crucial in many real-life applications, such as pulp and paper production. Current understanding of suspension flow dynamics remains poor and incomplete, resulting in conservative design of industrial equipments, low energy efficiency and equipment oversizing. In this paper, the most recent advancements in modelling and experimentation of fibre suspensions dynamics are presented. These advancements have been obtained in the framework of Action FP1005, funded by the COST Programme (European Cooperation in Science and Technology) to coordinate nationally-funded research on a European level. The Action aims at developing and validating numerical models for prediction of fibre suspensions as well as measurement techniques. The Action offers a forum to solve test cases and to compare simulated results to experiments, resulting in more reliable simulation tools to industry. Successfull introduction of such tool into industrial practice is crucial to innovate and increase competitivity of papermaking industry. [Preview Abstract] |
Tuesday, November 26, 2013 1:57PM - 2:10PM |
R7.00005: ABSTRACT WITHDRAWN |
Tuesday, November 26, 2013 2:10PM - 2:23PM |
R7.00006: An ensemble method for targeted adaptive observations applied to multiphase flows Zhizhao Che, Fangxin Fang, James Percival, Geoffrey Hewitt, Christopher Pain, Omar Matar, Michael Navon Many flow problems, such as turbulence and multiphase, are extremely complex due to their strong nonlinearity. It is important to simulate and measure different parameters accurately, such as pressure drops and flow rates, to which flow phenomena are very sensitive. Therefore, it is essential to put the sensors at the locations with larger impact, and to avoid locations with lower impact. Here, we proposed an ensemble method to estimate the impact of observations at different locations. Ensembles were generated by adding perturbations to the initial conditions, say. Different target functions were used to quantify the impact of observations. In comparing with other methods for estimating impact, this ensemble method is very simple to implement, and is independent of the definition of the target functions. This method is demonstrated by applying it to the one-dimensional Burgers equation. The next steps are to extend this method to various complex problems such as multiphase flows. [Preview Abstract] |
Tuesday, November 26, 2013 2:23PM - 2:36PM |
R7.00007: Generation of Pulsating Supercavities in a Rigid Wall Water Tunnel Grant Skidmore, Timothy Brungart, Jules Lindau The use of ventilated supercavities for underwater travel has many potential benefits, but before they can be fully exploited, obstacles in safe generation of a supercavitating body must first be overcome. The principle obstacle in this is determining the closure regime of the supercavity (re-entrant jet, twin vortex, or pulsating) from a given set of testing conditions. The re-entrant jet and twin vortex closure regimes are stable and should not create problems for the supercavitating body. Supercavity pulsation, however, is a self-excited resonance phenomenon that destabilizes the supercavity and leads to the periodic release of gas pockets at the tail of the cavity. Thus the phenomenon needs to be fully studied in a controlled environment. However, there are unanswered questions as to whether the pulsatory phenomenon may be properly obtained in a rigid-walled, closed-circuit water tunnel. Utilizing the 0.305 m and 1.219 m diameter water tunnels at ARL Penn State, an experimental study on both the pulsation phenomenon and the effects of tunnel blockage has been conducted. Here, we detail the findings of this study and discuss possible ways to mitigate the pulsation phenomenon. [Preview Abstract] |
Tuesday, November 26, 2013 2:36PM - 2:49PM |
R7.00008: The flow mechanism causing performance breakdown in cavitating axial turbomachines David Tan, Rinaldo Miorini, Elena Vagnoni, Ian Wilkes, Joseph Katz Cavitation degrades the performance of pumps, eventually leading to complete performance breakdown. Identifying the mechanisms causing breakdown has been a long-standing challenge. Using high-speed imaging (9.6 kHz) and pressure fluctuation measurements in the JHU optically refractive index matched facility, we elucidate the cavitation breakdown process in a waterjet pump. It involves interactions of a cavitating tip leakage vortex with the trailing edge of attached cavitation on the rotor blade, specifically, entrainment of the vortical cloud cavitation by the tip vortex. As the pressure is decreased, the blade suction side (SS) sheet cavitation extends further downstream. When the trailing edge extends to the region where the rotor blades overlap, the entrained sheet cavitation vorticity forms a vortex with axis aligned perpendicularly to the blade, and extending over the entire passage. Decreasing the pressure increases the size of this vortex and generates several parallel structures. The process causes a sharp drop in the pressure difference across the blade tip, i.e. the blade loading (performance) diminishes. Examination of previously published images of cavitation in rocket inducers suggests that this phenomenon occurs in other axial turbomachines as well. [Preview Abstract] |
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