Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session H19: Multiphase Flows: General I |
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Chair: Roger Arndt, University of Minnesota Room: 28E |
Monday, November 19, 2012 10:30AM - 10:43AM |
H19.00001: ABSTRACT WITHDRAWN |
Monday, November 19, 2012 10:43AM - 10:56AM |
H19.00002: Regarding Multispecies Diffusion and Gradient Driven Transport Erik Vold A theoretical framework for multispecies fluid transport has been long established in the Maxwell-Stefan equations but interpretations and solution methods appear in the literature to be quite varied. A framework is summarized here for mass drift of species which can include ionized gases with large differences in atomic mass driven by temperature, pressure, and electric potential gradient forces in addition to the usual diffusion driven by concentration gradients. The zero sum over species of mass drift flux closes the $(n_{s} -- 1)$ independent species drift equations for the $n_{s}$ species and ensures a non-zero molar flux summed over species of different atomic mass. This non-zero species molar flux leads to pressure perturbations, which require a compressible fluids computation to correctly account for the mass average flow and density relaxation. Computations in an initially isothermal binary mixing case illustrate the relaxation of the interfacial density profile by the mass averaged velocity arising from a divergent velocity field. Pressure perturbations associated with boundary reflections and viscosity are shown to have a negligible contribution to the density relaxation compared to the non-zero velocity divergence due to the expansion of each gas during the diffusion. An energy flux, consistent with the species mass diffusion leads to a significant temperature perturbation dominated by a bulk fluid PdV work term rather than the sum over species enthalpy flux. An example for binary diffusion across an interface between species with a large atomic mass difference shows a large asymmetry in species concentration profile unless properly constrained to a net zero sum over species mass flux. [Preview Abstract] |
Monday, November 19, 2012 10:56AM - 11:09AM |
H19.00003: Modeling of the Longitudinal Motion of a High Speed Supercavitating Vehicle David Escobar, Gary Balas, Roger Arndt High speed supercavitating vehicles offer challenges regarding modeling and control. A mathematical model of the longitudinal motion of a supercavitating test vehicle composed of a cylindrical body, a disk cavitator, and two fins is derived with the aid of experimental data acquired in a high speed water tunnel. The model considers the effect on the vehicle motion of a perturbed flow generated by an oscillating foil gust generator that emulates the effect of flying in the proximity of the sea surface. The vehicle equations of motion and experiments suggest that the fins provide the means for vehicle stability as well as control authority whereas the cavitator only provides control. It was also found that flow oscillations can be modeled as perturbations to the fin angle of attack since variations of the cavitator angle of attack due to the perturbed flow do not contribute to the moments about the vehicle center of gravity. Moreover, an initial view of planing forces generated through large variations of cavitator angle of attack are also presented here. The mathematical description of the vehicle dynamics enables the design of control laws and simulation of the vehicle motion subject to flow perturbations. This research is supported by a grant from the Office of Naval Research. [Preview Abstract] |
Monday, November 19, 2012 11:09AM - 11:22AM |
H19.00004: Experimental Validation of Control Systems for a high Speed Supercavitating Vehicle Roger Arndt, David Escobar, Ellison Kawakami, Gary Balas Testing of control systems for a high speed supercavitating vehicle (HSSV) is a challenge in terms of infrastructure and costs. An approach to the control validation of a supercavitating test vehicle is developed. The validation method, referred to as hybrid testing, combines simulation and experimental data in real-time to evaluate the HSSV control systems subject to perturbed flow in the high speed water tunnel at the Saint Anthony Falls Laboratory (Univ. of Minnesota). ~The test vehicle consists of a cylindrical body, two lateral wedge fins, a pitching disk cavitator used for control, and a ventilation system to insure a fully developed supercavity. A simulation computer uses measurements of the forces applied to the vehicle to compute the vehicle states utilized by the flight computer to control the vehicle simulated motion through the cavitator deflections, ~which in turn vary the forces applied to the test vehicle. ~The experimental results validate the suitability of the hybrid test platform, accuracy of the vehicle modeling and control design. as well as the effect of the perturbed flow on the closed-loop system performance. This research is supported by a grant from the Office of Naval Research. [Preview Abstract] |
Monday, November 19, 2012 11:22AM - 11:35AM |
H19.00005: Experimental study on gas-liquid bubbly turbulent flow in a large square duct HaoMin Sun, Tomoaki Kunugi, Hideo Nakamura Gas-liquid bubbly turbulent flow exists in many industrial areas. Therefore, many experiments for gas-liquid bubbly turbulent flow have been carried out in circular pipes for bubbly turbulent flow model. However, the cross-section of many flow passages are not the circular shape. Since the secondary flow of 2nd kind for single phase turbulent flow in a non-circular duct is well-known, the interaction between the secondary flow of 2nd kind and bubbles in gas-liquid bubbly turbulent flow in the non-circular duct could play an important role. In this study, in order to validate gas-liquid bubbly turbulent flow model in the non-circular duct, measurements were performed in a large square (136mm x 136mm) duct with duct length of 2.8m. The distributions of primary velocity, void fraction and turbulent Reynolds stresses were measured by a hot film probe. It is well-known that the primary velocity distribution of the bubbly flow in a circular pipe has a peak in the pipe center. In contrast, it was found that the primary velocity peaked near the corner of the square duct. In addition, primary velocity distribution changes under various flow conditions were discussed by measuring data of the void fraction and turbulent Reynolds stresses. [Preview Abstract] |
Monday, November 19, 2012 11:35AM - 11:48AM |
H19.00006: Circumventing Imprecise Geometric Information and Development of a Unified Modeling Technique for Various Flow Regimes in Capillary Tubes Bahman Abbasi Owing to their manufacturability and reliability, capillary tubes are the most common expansion devices in household refrigerators. Therefore, investigating flow properties in the capillary tubes is of immense appeal in the said business. The models to predict pressure drop in two-phase internal flows invariably rely upon highly precise geometric information. The manner in which capillary tubes are manufactured makes them highly susceptible to geometric imprecisions, which renders geometry-based models unreliable to the point of obsoleteness. Aware of the issue, manufacturers categorize capillary tubes based on Nitrogen flow rate through them. This categorization method presents an opportunity to substitute geometric details with Nitrogen flow data as the basis for customized models. The simulation tools developed by implementation of this technique have the singular advantage of being applicable across flow regimes. Thus the error-prone process of identifying compatible correlations is eliminated. Equally importantly, compressibility and chocking effects can be incorporated in the same model. The outcome is a standalone correlation that provides accurate predictions, regardless of any particular fluid or flow regime. Thereby, exploratory investigations for capillary tube design and optimization are greatly simplified. [Preview Abstract] |
Monday, November 19, 2012 11:48AM - 12:01PM |
H19.00007: PIV in the two phases of hydrodynamic cavitation in a venturi type section Sylvie Fuzier, S\'ebastien Coudert, Olivier Coutier Delgosha The presence of cavitation can affect the performance of turbomachinery. Attached sheet cavities on the blades induce modifications of flow dynamics and turbulence properties. This phenomenon is studied here in a configuration of 2D flow in a venturi type section. Images of the bubbles as well as of the light emitted by fluorescent particles placed in the liquid are recorded simultaneously. Velocities of the bubbles and of the liquid phase are obtained by PIV. The slip velocity is analyzed function of the number of cavitation and other physical parameters. Different levels of turbulence are correlated with different bubble structures in the dipahasic cavity. [Preview Abstract] |
Monday, November 19, 2012 12:01PM - 12:14PM |
H19.00008: High-order accurate interface-capturing schemes for gas-liquid flows: pressure and temperature considerations Eric Johnsen Direct simulations of the inertial collapse and rebound of a cavitation bubble are challenging due to the necessity to accurately represent discontinuities (e.g., interfaces and shock waves) and transport processes. A direct application of shock-capturing schemes is known to lead to spurious pressure oscillations and may further generate temperature and conservation errors. The present focus is on high-order accurate schemes (e.g., Weighted Essentially Non-Oscillatory or Discontinuous Galerkin) for interface capturing, which, in analogy to shock capturing, regularize material discontinuities over a few grid points while preserving interfacial conditions. Although approaches have been developed to prevent spurious pressure oscillations in the Euler equations by appropriately coupling a transport equation, temperature spikes may be generated, which in turn lead to transient pressure errors in Navier-Stokes simulations or erroneous mass transfer rates during phase change. These errors are analyzed in the context of gas/liquid and vapor/liquid flows. By appropriately transporting the relevant parameters of a stiffened equation of state, pressure, temperature and conservation errors can be prevented. Results pertaining to cavitation-bubble collapse will be presented. [Preview Abstract] |
Monday, November 19, 2012 12:14PM - 12:27PM |
H19.00009: Direct numerical simulation of turbulent supercritical flow and heat transfer of water in a vertical pipe Jung Yul Yoo, Sang Hoon Lee, Joong Hun Bae Turbulent heat transfer to supercritical-pressure water flowing in a heated vertical tube is investigated using direct numerical simulation. A conservative space-time discretization scheme for variable-density flows at low Mach numbers is adopted to treat steep variations of fluid properties at supercritical pressure just above the thermodynamic critical point, where the fluid properties at such conditions are obtained using PROPATH and used in the form of tables. The buoyancy influence induced by strong variation of density across the pseudo-critical temperature proves to play an important role in turbulent flow and heat transfer at supercritical state. The predicted wall temperature shows localized peaks in the axial distribution. Localized heat transfer impairment of the supercritical-pressure water is found to occur where turbulent energy diffusion is locally suppressed due to the influence of buoyancy. Although the present DNS has been performed at a much lower Reynolds number than that of typical experimental conditions, the peculiar characteristics of supercritical heat transfer including both enhancement and local deterioration are well predicted, in particular, the occurrence of double hot spots. [Preview Abstract] |
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