Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session GU: Multiphase Flows IV |
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Chair: Ken Kiger, University of Maryland Room: Hyatt Regency Long Beach Regency A |
Monday, November 22, 2010 8:00AM - 8:13AM |
GU.00001: Two-phase PIV measurements of particle suspension in a forced impinging jet Rahul Mulinti, Ken Kiger The condition of rotorcraft brownout is characterized by intense dust suspension that is uplifted during landing and takeoff operations in regions covered with loose sediment. To predict particle suspension and sedimentation within coupled particle-laden flows, detailed characterization of the micro-scale mechanics is needed within a prototypical flow that captures the essence of the rotorcraft/ground wake interactions. Two-phase PIV has been used to study the interaction of a sediment bed made of glass spheres with characteristic flow structures reminiscent from flow within a rotor wake. In order to make reliable simultaneous two-phase PIV measurements, a phase discrimination algorithm from a single two-phase image has been implemented. The validity of the separation is checked by processing images that consisted only of the very small tracer particles, or only the dispersed phase particles, and examining how much ``cross-talk'' was present between the phases. The mobilization and wall-normal flux of particulates by the vortex-wall interaction will be reported for several different operational conditions, and correlated to the local vortex conditions. [Preview Abstract] |
Monday, November 22, 2010 8:13AM - 8:26AM |
GU.00002: Impingement of a Planar Shock Wave on a Dense Field of Particles Justin Wagner, Steven Beresh, Sean Kearney, Wayne Trott, Jaime Castaneda, Brian Pruett, Melvin Baer A novel multiphase shock tube has recently been developed to study particle dynamics in gas-solid flows having particle volume fractions that reside between the dilute and granular regimes. The method for introducing particles into the tube involves the use of a gravity-fed contoured particle seeder, which is capable of producing dense fields of spatially isotropic particles. The facility is capable of producing planar shocks having a maximum shock Mach number of about 2.1 that propagate into air at initially ambient conditions. The primary purpose of this new facility is to provide high fidelity data of shock-particle interactions in flows having particle volume fractions of about 1 to 50{\%}. To achieve this goal, the facility drives a planar shock into a spatially isotropic field, or curtain, of particles. Experiments are conducted for two configurations where the particle curtain is either parallel to the spanwise, or the streamwise direction. Arrays of high-frequency-response pressure transducers are placed near the particle curtain to measure the attenuation and shape change of the shock owing to its interaction with the dense gas particle field. In addition, simultaneous high-speed imaging is used to visualize the impact of the shock on the particle curtain and to measure the particle motion induced downstream of the shock. [Preview Abstract] |
Monday, November 22, 2010 8:26AM - 8:39AM |
GU.00003: Multiphysics Simulations of Hot-Spot Initiation in Shocked Insensitive High-Explosive Fady Najjar, W.M. Howard, L.E. Fried Solid plastic-bonded high-explosive materials consist of crystals with micron-sized pores embedded. Under mechanical or thermal insults, these voids increase the ease of shock initiation by generating high-temperature regions during their collapse that might lead to ignition. Understanding the mechanisms of hot-spot initiation has significant research interest due to safety, reliability and development of new insensitive munitions. Multi-dimensional high-resolution meso-scale simulations are performed using the multiphysics software, ALE3D, to understand the hot-spot initiation. The Cheetah code is coupled to ALE3D, creating multi-dimensional sparse tables for the HE properties. The reaction rates were obtained from MD Quantum computations. Our current predictions showcase several interesting features regarding hot spot dynamics including the formation of a ``secondary'' jet. We will discuss the results obtained with hydro-thermo-chemical processes leading to ignition growth for various pore sizes and different shock pressures. [Preview Abstract] |
Monday, November 22, 2010 8:39AM - 8:52AM |
GU.00004: A high-resolution numerical method for supercritical flows Hiroshi Terashima, Soshi Kawai, Nobuhiro Yamanishi We present a high-resolution methodology using a higher-order compact differencing scheme with localized artificial diffusivity for simulating cryogenic turbulent mixing flows under supercritical thermodynamic conditions. One-dimensional advection and modified Shu-Osher problems in supercritical flows are proposed to assess the performance of the present method. Results for the advection problem show that the present method is successfully applied to supercritical flows, including a trans- critical state, without any significant spurious oscillations, if initial startup errors are avoided. A localized artificial diffusivity, especially artificial thermal conductivity for temperature gradients, effectively works on reducing numerical wiggles produced due to high density/temperature gradients at interfaces. The modified Shu-Osher problem demonstrates the superiority of the present method in resolving high-frequency fluctuations as compared to a conventional upwind-biased scheme. Results for a two-dimensional cryogenic plane jet in a supercritical pressure condition also demonstrate the capability of the present method for simulating the unsteady jet flow structures and the superiority for resolving the fluctuations with reasonable grid resolutions. [Preview Abstract] |
Monday, November 22, 2010 8:52AM - 9:05AM |
GU.00005: Evaporation of thin liquid films into air Vladimir Ajaev, David Brutin, Lounes Tadrist We develop a mathematical model of evaporation of a thin liquid film into air under the action of disjoining pressure. The rate of evaporation is determined from the numerical solution of a coupled system of equations describing heat conduction in the liquid and diffusion of vapor through air. Local vapor concentration near the film surface is assumed equal to its equilibrium value at the local temperature. Evolution of the film is studied for two commonly used disjoining pressure models. Conditions are formulated at which disjoining pressure suppresses evaporation. The model is applied to investigation of the effect of evaporation on contact lines on heated surfaces. [Preview Abstract] |
Monday, November 22, 2010 9:05AM - 9:18AM |
GU.00006: Confined two-phase flows in the presence of evaporation and condensation Roman Grigoriev, Tongran Qin While Rayleigh-B\'enard and Marangoni convection in liquid layers with a free surface has been studied quite extensively in the absence of phase change, convection in the presence of evaporation/condensation, especially in confined geometries, is not as well understood. In this talk we discuss a transient finite-volume numerical model of a confined liquid film in local equilibrium with its vapor subject to a termperature gradient where the solutions for both the position of the liquid-vapor interface and the interfacial temperature are consistent with the mass and heat transport in the bulk. One important result of this model is that interfacial temperature develops extremely sharp gradients near the solid-liquid-vapor contact lines at arbitrary contact angles. This result has dramatic consequences for the locations where both phase change and thermocapillary effects are significant at the free surface. We conjecture that accurate description of the problem requires the use of a local model (such as the similarity solutions of Morris [J. Fluid Mech. 411:59 (2000)]) near the contact line. [Preview Abstract] |
Monday, November 22, 2010 9:18AM - 9:31AM |
GU.00007: The effects of fluid turbulence on metal vapor nucleation Jun Liu, Sean Garrick The rising need for clean, renewable energy sources has led to recent studies on hydrogen production via hydrolysis of zinc nanoparticles. Aerosol or gas-phase processes are favored in many industrial applications due to its advantage in controlling particle size distribution and the resultant chemical conversion. The rising need for clean, renewable energy sources has led to recent studies on hydrogen production via hydrolysis of zinc nanoparticles. Aerosol or gas-phase processes are favored in many industrial applications due to its advantage in controlling particle size distribution and the resultant chemical conversion. In this work we study the formation of metal particles in a shear flows. Direct numerical simulation of homogeneous metal vapor nucleation in laminar and turbulent flows are performed for a variety of metals. The flows consist of hot metal vapor issuing into cooler inert gas. As the metal vapor cools, nanoparticles form and are transported throughout the flow-field. Homogeneous nucleation is simulated using classical nucleation theory and two approaches to representing the surface tension. The effects of three-dimensional turbulent mixing are also analyzed. The results suggest that fluid, thermal and species mixing greatly affects the nucleation dynamics. We report on the effects of vapor concentration level, fluid mixing, and particle surface tension on the conversion from metal vapor to metal nanoparticles. [Preview Abstract] |
Monday, November 22, 2010 9:31AM - 9:44AM |
GU.00008: Full-Eulerian fluid-structure coupling simulation of hyperelastic channel flow Naohiro Nagano, Kazuyasu Sugiyama, Shintaro Takeuchi, Satoshi Ii, Shu Takagi, Yoichiro Matsumoto A full-Eulerian simulation for coupling a Newtonian fluid and hyperelastic material is conducted. The system involves an interaction problem between the fluid and hyperelastic walls and is driven by pressure difference, mimicking a blood flow in a blood vessel. A single set of the governing equations for the fluid and solid is employed, and a volume-of-fluid idea is employed to describe a multi-component geometry. The solid stress is defined in Eulerian frame by using a left Cauchy-Green deformation tensor, and the temporal change in the solid deformation is described by updating the tensor. The method employs a uniform fixed grid system for both fluid and solid and it does not require any mesh generation or reconstruction, aiming at facilitating the practical bio-mechanical fluid-structure analysis based on a medical image. The validity of the simulation results is established through comparison with a theoretical prediction. As an application of the present method, pulsating flows are simulated to demonstrate a nonlinear behavior of the flow rate on the pulsating amplitude, and an effect of employing an anisotropic hyperelastic material is discussed. [Preview Abstract] |
Monday, November 22, 2010 9:44AM - 9:57AM |
GU.00009: Distribution Coefficient Algorithm for Small Mass Nodes in Material Point Method for Multi-Phase Flow Xia Ma, Balaji Jayaraman, Paul Giguere, Duan Zhang One of the advantages of the Material Point Method (MPM) is its capability to simulate large material deformation and flows without the need to advect state variables, such as stress and strain of the material through an Eulerian mesh. Without numerical diffusion associated with such advection, MPM can keep sharp interface without smearing them. MPM also avoids distortion and entanglement of meshes associated with Lagrange methods in the case of a large deformation. However, the straightforward MPM has its own disadvantages. When a material just enters a new cell, it can cause a very small mass on the nodes near the material boundary. As the denominator in the calculation of the acceleration, this small mass can cause numerical instability and leads to artificially large acceleration. The present work deals with this numerical instability by transferring the force away from the small mass nodes in a manner consistent with the errors of the original MPM calculation. This treatment significantly improves the stability of multi-phase flow simulation using MPM. The numerical cost of this algorithm is negligible considering the computational time saved by the significantly increased time step size. We provide comparisons between the results calculated with and without this improvement to MPM. Release number: LA-UR 10-05193. [Preview Abstract] |
Monday, November 22, 2010 9:57AM - 10:10AM |
GU.00010: Material point method to fluid-structure interactions Duan Zhang, Xia Ma, Paul Giguere Fluid-structure interactions are common in nature and in engineering practice. Numerical simulation of these phenomena has been difficult not only because of the need to track interfaces, but also because of the need to model material interactions on the interface region. Furthermore, if the solid material is a porous material, material interactions occur not only on the interface region, but also inside the body of the materials. Recently, this type of problems has been studied using a continuous multiphase flow theory. Material point method (MPM) has been found to be a handy tool for these calculations. The material point method is an advanced version of the particle in cell (PIC) method. Recent developments of the method have significantly improved its stability and accuracy for this type of calculations. The use of the method to fluid-structure interaction problems has produced many promising results. In this talk we will briefly introduce the recent developments of MPM and shown examples of its applications. [Preview Abstract] |
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