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Proceedings Papers

*Proc. ASME*. FEDSM2017, Volume 1C, Symposia: Gas-Liquid Two-Phase Flows; Gas and Liquid-Solid Two-Phase Flows; Numerical Methods for Multiphase Flow; Turbulent Flows: Issues and Perspectives; Flow Applications in Aerospace; Fluid Power; Bio-Inspired Fluid Mechanics; Flow Manipulation and Active Control; Fundamental Issues and Perspectives in Fluid Mechanics; Transport Phenomena in Energy Conversion From Clean and Sustainable Resources; Transport Phenomena in Materials Processing and Manufacturing Processes, V01CT14A001, July 30–August 3, 2017

Paper No: FEDSM2017-69022

Abstract

Models and simulations are employed to analyze the motion of a spring-supported piston in a vibrated liquid-filled cylinder. The piston motion is damped by forcing liquid through a narrow gap between a hole through the piston and a post fixed to the housing. As the piston moves, the length of this gap changes, so the piston damping coefficient depends on the piston position. This produces a nonlinear damper, even for highly viscous flow. When gas is absent, the vibration response is overdamped. However, adding a little gas changes the response of this spring-mass-damper system to vibration. During vibration, Bjerknes forces cause some of the gas to migrate below the piston. The resulting pneumatic spring enables the liquid to move with the piston so as to force very little liquid through the gap. Thus, this “Couette mode” has low damping and a strong resonance near the frequency given by the pneumatic spring constant and the total mass of the piston and the liquid. Near this frequency, the amplitude of the piston motion is large, so the nonlinear damper produces a large net force on the piston. To analyze the effect of this nonlinear damper in detail, a surrogate system is developed by modifying the original system in two ways. First, the gas regions are replaced by upper and lower bellows with similar compressibility to give a well-defined “pneumatic” spring. Second, the upper stop against which the piston is pushed by its lower supporting spring is replaced with an upper spring, thereby removing the nonlinearity from the stop. An ordinary-differential-equation (ODE) drift model based on quasi-steady Stokes flow is used to produce a regime map of the vibration amplitudes and frequencies for which the piston is up or down for conditions of experimental interest. These results agree fairly well with Arbitrary Lagrangian Eulerian (ALE) simulations of the incompressible Navier-Stokes (NS) equations for the liquid and Newton’s 2 nd Law for the piston and bellows. A quantitative understanding of this nonlinear behavior may enable the development of novel tunable dampers for sensing vibrations of specified amplitudes and frequencies.

Proceedings Papers

*Proc. ASME*. AJKFluids2015, Volume 1A: Symposia, Part 2, V01AT14A005, July 26–31, 2015

Paper No: AJKFluids2015-15106

Abstract

The coalescence of droplets in creeping flow through a tube was experimentally examined. The coalescence time of two droplets and the diameter of the clearance area between the droplets were measured. The experimentally measured coalescence times were compared with those determined by semi-theoretical formulas and generally good agreement was observed between the two. The effect of the Reynolds number of the creeping flow on the coalescence of the droplets was also investigated.

Proceedings Papers

*Proc. ASME*. FEDSM2014, Volume 1D, Symposia: Transport Phenomena in Mixing; Turbulent Flows; Urban Fluid Mechanics; Fluid Dynamic Behavior of Complex Particles; Analysis of Elementary Processes in Dispersed Multiphase Flows; Multiphase Flow With Heat/Mass Transfer in Process Technology; Fluid Mechanics of Aircraft and Rocket Emissions and Their Environmental Impacts; High Performance CFD Computation; Performance of Multiphase Flow Systems; Wind Energy; Uncertainty Quantification in Flow Measurements and Simulations, V01DT30A004, August 3–7, 2014

Paper No: FEDSM2014-21634

Abstract

The physics of transport, deposition, detachment and reentrainment re-entrainment of particles suspended in a fluid are of great interests in many practical fluid engineering problems. For spherical particles, analysis of their translational motions is sufficient for a complete description of their transport processes. Prediction of transport and deposition of non-spherical particles, however, is more complicated due to the coupling of particle translational and rotational motions. Most studies related to dispersion of ellipsoidal particles used the traditional creeping flow formulations for hydrodynamic forces and torques. These formulations are valid for very low Reynolds number flows. In this study, dispersion and deposition of ellipsoidal particles in a fully developed laminar pipe flow are analyzed numerically using new correlations for hydrodynamic forces and torques. The deposition efficiency of the ellipsoidal particles in laminar pipe flow are calculated and the results are compared with other theoretical and numerical studies and good agreement is observed.

Proceedings Papers

*Proc. ASME*. FEDSM2013, Volume 1A, Symposia: Advances in Fluids Engineering Education; Advances in Numerical Modeling for Turbomachinery Flow Optimization; Applications in CFD; Bio-Inspired Fluid Mechanics; CFD Verification and Validation; Development and Applications of Immersed Boundary Methods; DNS, LES, and Hybrid RANS/LES Methods, V01AT02A003, July 7–11, 2013

Paper No: FEDSM2013-16155

Abstract

We present a topology optimization method for the Stokes problem under multiple flow cases by an improved level set method. In the framework of level set method, an implicit reinitialization approach is developed by deriving a new formula for the smoothing parameter in the conventional reinitialization equation. And a spline-free parameterization re-meshing method is adopted to overcome the convergence difficulty in flow analysis and guarantee the direct loading of the no-slip boundary condition. The topology optimization method developed in this paper is used to implement the optimal design for Stokes flow with the different boundary conditions. Numerical examples demonstrate that the proposed approach is effective and robust for the topology optimization of Stokes problem under multiple flow cases.

Proceedings Papers

*Proc. ASME*. FEDSM2010, ASME 2010 7th International Symposium on Fluid-Structure Interactions, Flow-Sound Interactions, and Flow-Induced Vibration and Noise: Volume 3, Parts A and B, 967-974, August 1–5, 2010

Paper No: FEDSM-ICNMM2010-30636

Abstract

The mechanical behavior of a eukaryotic cell is mainly determined by its cytoskeleton. Microtubules immersed in cytosol are a central part of the cytoskeleton. Cytosol is the viscous fluid in living cells. The microtubules permanently oscillate in the cytosol. In this study, two-dimensional vibration of a single microtubule in living cell is investigated. The Donnell’s shell theory equations for orthotropic materials is used to model the microtubule whereas the motion of the cytosol is modeled as Stokes flow characterized by a small Reynolds number with no-slip condition at microtubule-cytosol interface. The stress field in the cytosol induced by vibrating microtubule is determined analytically and the coupled vibrations of the microtubule-cytoplasm system are investigated. A coupled polynomial eigenvalue problem is developed in the present study and the variations of eigenvalues of coupled system with cytosol dynamic viscosity, microtubule circumferential Young’s modulus and circumferential wave number are examined.

Proceedings Papers

*Proc. ASME*. FEDSM2010, ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 1, Symposia – Parts A, B, and C, 2773-2783, August 1–5, 2010

Paper No: FEDSM-ICNMM2010-30303

Abstract

Continuous subcutaneous insulin infusion (CSII) therapy, also known as insulin pump therapy, has become an important advancement in diabetes therapy to improve the quality of life for millions of diabetes patients. Insulin delivery failures caused by the precipitations of insulin within micro-sized CSII tubing systems have been reported in recent years. It has also been conjectured that the flow of insulin through an insulin infusion set may be reduced or inhibited by air bubbles entrained into the capillary CSII tubing system during the typical three- to five-day operation between refills. Currently, most solutions to insulin occlusion related problems are based on clinical trials. In the present study, an experimental and theoretic study was conducted to investigate the pulsed flows inside the micro-sized CSII tubing system. A micro-PIV system was used to provide detailed flow velocity field measurements inside the capillary CSII tubing system to characterize the transient behavior of the micro-flows upon the pulsed actuation of the insulin pump used in CSII therapy. It was found that the microflow inside the CSII tubing system is highly unsteady, which is much more interesting than the creeping flow that the nominal averaged flow rates would suggest. A theoretic frame work was also performed to model the pulsed micro-flows driven by the insulin pump to predict the transient behavior of the microflows and velocity distributions inside the micro-sized CSII tubing system. The measurement results and the theoretic predictions were compared quantitatively to elucidate underlying physics for a better understanding of the microphysical process associated with the insulin delivery in order to provide a better guidance for troubleshooting of insulin occlusion in CSII therapy.

Proceedings Papers

*Proc. ASME*. FEDSM2009, Volume 2: Fora, 555-560, August 2–6, 2009

Paper No: FEDSM2009-78548

Abstract

In this paper we present results of an experimental investigation that explores the transient filling of nanochannels due to capillarity. The nanochannels explored here were fabricated using sacrificial metal cores and were designed to mimic the parallel-plate channel geometry. Channels of heights ranging from 41 to 91 nm were utilized in the experimental program and both aluminum and chromium were utilized as the sacrificial metal from which the channels were formed. The filling dynamics of channels that were closed on one end were also explored. The data reveal that the channels fabricated with aluminum as the sacrificial core yield marked departure from expected behavior, with the apparent frictional constant significantly elevated above classical values. Potential reasons for the departure are discussed. Channels fabricated with chromium cores result in behavior that yields much less deviation from anticipated Stokes flow behavior. However, for these channels the meniscus speed is observed to vary markedly across the channels transverse width. Channels that are closed on one end yield behavior that is significantly different from the open-ended channel results. Here the meniscus becomes destabilized as it approaches the capped channel end and the trapped air becomes entrained by the liquid and dispersed without evidence of bubble existence.

Proceedings Papers

*Proc. ASME*. FEDSM2009, Volume 1: Symposia, Parts A, B and C, 917-930, August 2–6, 2009

Paper No: FEDSM2009-78402

Abstract

A new equation of motion is applied to bubbles and sand particles injected near the wall in a direct numerical simulation of a turbulent boundary layer of water. The surface-forces are considered systematically to assess their effect on particle motion, concentration, diffusion rates, and Lagrangian statistics. The results show that strong lift forces can be obtained when the particle’s terminal velocity is aligned with the freestream direction but only small effects are obtained if the terminal velocity is directed away from the wall. While finite Reynolds number effects are found to be small for the quasi-steady drag force, the choice of history force model is quite sensitive—an effect attributed to the long “memory” of the creeping flow expression. In general, the Lagrangian statistics were found to be the most sensitive output, sometimes varying largely between choice of surface-forces.

Proceedings Papers

*Proc. ASME*. HT-FED2004, Volume 1, 955-963, July 11–15, 2004

Paper No: HT-FED2004-56451

Abstract

This paper aims at investigating the effect of various boundary velocity distributions on the flow field in Stokes flow of incompressible fluids flow with axisymmetry. It was reported in literature that if the velocity variation at a plane boundary is suitably prescribed, the whole field of Stokes flow in a half-plane can be identified immediately by the artifice of Laplace transform. Similarly, it can be shown that if the boundary velocity distribution is represented for an axisymmetrical half-space, the whole field of Stokes flow can be described by the use of Hankel transform. With suitable given boundary velocity variations, the exact solution can be obtained through the integration of the resulting inverse transform. In this paper several realistic, continuous and discontinuous boundary velocity variations are analyzed following an intuitive derivative of the exact solution in cylindrical coordinates. The variations of the velocities and the pressure in the fluid are obtained for several examples of particular velocity variations at the plane boundary.

Proceedings Papers

*Proc. ASME*. HT-FED2004, Volume 2, Parts A and B, 663-674, July 11–15, 2004

Paper No: HT-FED2004-56327

Abstract

Recently, we have developed multi-level boundary element methods (MLBEM) for the solution of the Laplace and Helmholtz equations that involve asymptotically decaying non-oscillatory and oscillatory singular kernels, respectively. The accuracy and efficiency of the fast boundary element methods for steady-state heat diffusion and accoustics problems have been investigated for square domains. The current work extends the MLBEM methodology to the solution of Stokes equation in more complex two dimensional domains. The performance of the fast boundary element method for the Stokes flows is first investigated for a model problem in a unit square. Then, we study the performance of the MLBEM algorithm in a C-shaped domain.

Proceedings Papers

*Proc. ASME*. FEDSM2003, Volume 2: Symposia, Parts A, B, and C, 415-421, July 6–10, 2003

Paper No: FEDSM2003-45154

Abstract

In this paper results of direct numerical simulation (DNS) of bubbles rising in viscous Newtonian liquids with high-density ratio are presented. The simulations are carried out with the highly parallelized code FS3D, which employs the Volume-of-Fluid (VOF) method. The high degree of parallization of the code allows high resolution of the computational domain, such that the Kolmogorov length scale inside the liquid phase is resolved for the simulations. For validation of the numerical results the terminal rise velocities, bubble shapes and flow fields are compared to experimental data as well as to approximate analytical solutions. For high Morton numbers terminal rise velocities and aspect ratios agree very well with experimental values. For lower Morton numbers there is an increasing difference between experimental and numerical rise velocities. The aspect ratios of ellipsoidal bubbles match both with experimental measurements and with theoretical values of Taylor and Acrivos. At very low Reynolds numbers (Re B < 1) the velocity fields in and outside of the bubble show good semi-quantitative agreement with the analytical creeping flow solution of Hadamard and Rybczynski.

Proceedings Papers

*Proc. ASME*. FEDSM2003, Volume 1: Fora, Parts A, B, C, and D, 349, July 6–10, 2003

Paper No: FEDSM2003-45711

Abstract

Energy and momentum exchange between spherical particles and a fluid is a fundamental problem that has excited the intellectual curiosity of many scientists for more than two centuries. The development of the energy equation of spherical particles in a fluid can be traced back to the work of Laplace and Fourier that appeared early in the 19 th century. It is now little known that Peclet formulated the no-slip condition at a solid boundary, by observing the transfer of heat, approximately ten years before the concept of viscosity was conceived. Towards the middle of the 19 th century Poison derived the hydrodynamic force on a sphere in an inviscid fluid and a few years later, Stokes formulated what is now known “the Stokes drag” for the steady-state hydrodynamic force acting on a spherical particle in a viscous fluid. Boussinesq and Basset developed a form for the transient equation of motion of the particles with very low inertia towards the end of the 19 th century. The mathematical advances of the early 20 th century are reflected in developments in mechanics and on the equation of motion of particles. Oseen and Faxen used asymptotic methods to derive improved our knowledge on the behavior of particles with inertia and in close proximity to boundaries. Experimentation contributed very useful correlations on the hydrodynamic force and the heat transfer from particles. The experimentally derived data helped also in the development of semiempirical equations for the transient hydrodynamic force. Regular and singular perturbation methods have been used more recently to derive expressions for the transient hydrodynamic force and the heat transfer from particles during time-dependent processes, both under creeping flow conditions and at low Reynolds or Peclet numbers. The recent advances on computational methods and the exponential increase in computer power enable us to simulate the motion and energy exchange of groups of particles and complex particle interactions. This presentation gives a historical perspective on the development of our knowledge on particle motion and heat transfer inside a viscous or conducting fluid. Emphasis is given on the exposition of the lesser-known works of the 19 th century that have placed the foundation for many concepts and methods that are still used today. The presentation concludes with the most recent contributions of the numerical studies and a short exposition of the voids in our knowledge on energy and momentum exchange processes between particles and a fluid.

Proceedings Papers

*Proc. ASME*. FEDSM2003, Volume 1: Fora, Parts A, B, C, and D, 351-352, July 6–10, 2003

Paper No: FEDSM2003-45713

Abstract

One of the challenges in the numerical simulation of a system of particles in a fluid flow is to balance the need for an accurate representation of the flow around individual particles with the feasibility of simulating the fully-coupled dynamics of large numbers of particles. Over the past few years, several techniques have been developed for the direct numerical simulation of dispersed two-phase flows. Examples include the ALE-FEM formulation described by Hu et al. [1] and the DLM method of Patankar et al. [2]. The former uses a finite element mesh that conforms to the shape and position of each particle and evolves dynamically as the particles move, while the latter employs a fixed mesh and constraints are imposed in the volume of fluid occupied by the particle to reproduce a corresponding rigid body motion. In both the aim is to fully resolve the flow dynamics for each particle and there is a corresponding demand for high resolution of the flow. A typical approach used for gas-solid flows has been the point-force method that combines a Lagrangian tracking of individual particles with an Eulerian formulation for force feedback on the fluid flow. The latter approach has worked well for very small particles in systems of negligible void fraction but significant mass loading. The resolution level is very low and often the particles are smaller than the spacing between grid points. Its success comes from the averaging effect of large numbers of small particles and the fact that the influence of an individual particle is weak. The approach though is inaccurate for liquid-solid or bubbly flows when the individual particles are of finite size and the void fractions may easily be larger than 1%. In tracking the individual particles an equation of motion is formulated that relates the particle acceleration to the fluid forces acting on the particle, and these forces such as drag and lift are parameterized in terms of the local fluid velocity, velocity gradients and history of the fluid motion. Once flow modification is included however, it is harder to specify the local flow. The parameterizations also become more complex as effects of finite Reynolds number or wall boundaries are included. As a numerical procedure, the force-coupling method (FCM) does not require the same level of resolution as the DLM or ALE-FEM schemes and avoids the limitations of the point-force method. It gives a self-consistent scheme for simulating the dynamics of a system of small particle using a fixed numerical mesh and resolves the flow except close to the surface of each particle. Distributed, finite force-multipoles are used to represent the particles, and FCM is able to predict quite well the motion of isolated particles in shear flows and the interaction between moving particles. The method also provides insights into how the two-phase flow may be described theoretically and modeled. The idea of the force-coupling method was first introduced by Maxey et al. [3]. The basic elements of the method are given by Maxey & Patel [4] and Lomholt & Maxey [5]. In the basic version of the method, fluid is assumed to fill the whole flow domain, including the volume occupied by the particles. The presence of each particle is represented by a finite force monopole that generates a body force distribution f ( x , t ) on the fluid, which transmits the resultant force of the particles on the flow to the fluid. The velocity field u ( x , t ) is incompressible and satisfies ∇ · u = 0 ( 1 ) ρ Du Dt = − ∇ p + μ ∇ 2 u + f ( x , t ) , ( 2 ) where μ is the fluid viscosity and p is the pressure. The body force due to the presence of N P bubbles is f ( x , t ) = ∑ n = 1 N p F ( n ) Δ ( x − Y ( n ) ( t ) ) , ( 3 ) Y ( n ) ( t ) is the position of the n th spherical particle and F ( n ) ( t ) is the force this exerts on the fluid. The force monopole for each particle is determined by the function Δ( x ), which is specified as a Gaussian envelope Δ ( x ) = ( 2 π σ 2 ) − 3 / 2 exp ( − x 2 / 2 σ 2 ) ( 4 ) and the length scale σ is set in terms of the particle radius a as a /σ = π . The velocity of each particle V ( n ) ( t ) is found by forming a local average of the fluid velocity over the region occupied by the particle as V ( n ) ( t ) = ∫ u ( x , t ) Δ ( x − Y ( n ) ( t ) ) d 3 x . ( 5 ) If m P and m F denote the mass of a particle and the mass of displaced fluid, the force of the particle acting on the fluid is F ( n ) = ( m P − m F ) ( g − dV ( n ) dt ) . ( 6 ) This force is the sum of the net external force due to buoyancy of the particle and the excess inertia of the particle over the corresponding volume of displaced fluid. In addition a short-range, conservative force barrier is imposed to represent collisions between particles and prevent overlap. A similar barrier force is imposed, normal to the wall, to represent collisions between a particle and a rigid wall. With this scheme the body forces induce a fluid motion equivalent to that of the particles. The dynamics of the particles and the fluid are considered as one system where fluid drag on the particles, added-mass effects and lift forces are internal to the system. The method does not resolve flow details near to the surface of a particle, and indeed the no-slip condition is not satisfied on surface. At distances of about half a particle radius from the surface the flow though is fairly well represented. While there is no explicit boundary condition on the particle surface, the condition (5) ensures that the bubble and the surrounding fluid move together. The method has been applied to a variety of flow problems. Lomholt et al. [6] compared experimental results for the buoyant rise of particles in a vertical channel filled with liquid with results from corresponding simulations with FCM. The particle Reynolds numbers were in the range of 0 to 5 and the results agreed well. The wake-capture and the drafting, kissing and tumbling of pairs of particles, or of a group of three particles were found to match. Comparisons have made too with full direct numerical simulations performed with a spectral element code [7]. Liu et al. [8] examined the motion of particles in a channel at both low and finite Reynolds numbers, up to Re = 10. There was in general good agreement between the FCM results and the DNS for the particle motion, and the flow details were consistent away from the particle surface. There has been extensive work in the past on the sedimentation of particles in a homogeneous suspension, mainly for conditions of Stokes flow. Climent & Maxey [9] have verified that the FCM scheme reproduces many of the standard features found for Stokes suspensions. The results for finite Reynolds numbers illustrate how the structure of the suspension changes as fluid inertia is introduced, in particular limiting the growth in velocity fluctuation levels with system size. Further work has been done by Dance [10] on sedimenting suspensions in bounded containers. Recently we have been studying the dynamics of drag reduction by injecting micro-bubbles into a turbulent channel flow. This has been proven through experiments over the past 30 years to be an effective means for drag reduction but the details of the mechanisms involved have not been determined. Numerical simulations by Xu et al. [11] have shown clear evidence of drag reduction for a range of bubble sizes. A key feature is the need to maintain a concentration of bubbles in the near-wall region. In the talk, the method will be described and example results given. Specific issues relevant to gas-solid flows will be discussed.

Proceedings Papers

*Proc. ASME*. FEDSM2005, Volume 1: Symposia, Parts A and B, 929-935, June 19–23, 2005

Paper No: FEDSM2005-77187

Abstract

The motion of a rigid particle whose surface is a slightly deformed sphere is studied for creeping flows with the assumption of slip on the particle. Expressions are obtained for the hydrodynamic force and torque exerted by the fluid on a deformed sphere using an asymptotic method introduced by H. Brenner, wherein the normalized amplitude of the deviation from sphericity is assumed to be a small parameter. The Stokes’ resistance calculated by this method is validated by comparing with existing solutions the limiting cases of no slip and perfect slip. The equations describing the motion of a deformed sphere with a slip surface in a simple shear flow are also derived and solved. The motion of the deformed sphere is shown to differ significantly from the no-slip case for low values of a dimensionless parameter that incorporates the slip coefficient. The period of rotation of the deformed sphere is longer, and for cases where the slip coefficient is low, the spheroid rotates to a fixed angle and reaches a quasi-steady orientation.