Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session M28: Particle-laden Flows: Particle-Turbulence Interaction I |
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Chair: Evan Variano, University of California, Berkeley Room: F149 |
Tuesday, November 22, 2016 8:00AM - 8:13AM |
M28.00001: Rotations of long, inertialess rods in turbulence Nimish Pujara, Evan Variano, Greg Voth We present results on rotation of rods with lengths varying through the inertial range in turbulence. Rod motion is computed using one-way coupling in the Johns Hopkins University Turbulence Database of homogenous isotropic turbulence at $Re_{\lambda}=433$. We consider zero-volume, zero-inertia rods, whose motion we model by advecting two tracer particles with constant distance between them. By making the tumbling rate dimensionless with a timescale that corresponds to turbulent motions of the same size as the rod, we show that such motions are responsible for the most of the variance in rod tumbling. Flatness factors for tumbling show that large deviations from the mean tumbling rate become less frequent as rod length increases, suggesting that longer rods are less responsive to intermittent events in turbulence. Finally, to investigate how such rods respond to turbulent flow forcing at their scale, we calculate the coarse-grained velocity gradient tensor by fitting to the velocity field sampled at discrete points within the sphere that circumscribes the rod. Results of instantaneous rod alignment with the vorticity and strain-rate eigenvectors of this tensor enable us to understand the preferential orientation of rods with respect to the flow field they are experiencing. [Preview Abstract] |
Tuesday, November 22, 2016 8:13AM - 8:26AM |
M28.00002: A direct comparison of fully resolved and point-particle models in particle-laden turbulent flow Jeremy Horwitz, Mohammad Mehrabadi, Shankar Subramaniam, Ali Mani Point-particle methods have become a popular methodology to simulate viscous fluids laden with dispersed solid elements. Such methods may be contrasted with particle-resolved methods, whereby the boundary conditions between particles and fluid are treated exactly, while point-particle methods do not capture the boundary conditions exactly and couple the continuous and dispersed phase via point-forces. This allows point-particle methods to simulate particle-turbulence interaction at considerably lower resolution and computational cost than particle-resolved methods. However, lack of validation of point-particle methods begs the question of the predictive power of point-particle methods. In other words, can point-particle methods recover particle and fluid statistics compared with particle-resolved simulation of dynamically equivalent non-dimensional problems? We address this question in this work by examining decaying homogeneous isotropic turbulence laden with particles. For the same nominal conditions, we compare statistics predicted by a particle resolved method to those predicted by a point-particle method. We also examine the effect of the undisturbed velocity in the point-particle drag law by studying the same problem with a correction scheme. [Preview Abstract] |
Tuesday, November 22, 2016 8:26AM - 8:39AM |
M28.00003: The effect of wall geometry in particle-laden turbulent flow Hoora Abdehkakha, Gianluca Iaccarino Particle-laden turbulent flow plays a significant role in various industrial applications, as turbulence alters the exchange of momentum and energy between particles and fluid flow. In wall-bounded flows, inhomogeneity in turbulent properties is the primary cause of turbophoresis that leads the particles toward the walls. Conversely, shear-induced lift force on the particles can become important if large scale vortical structures are present. The objective of this study is to understand the effects of geometry on fluid flows and consequently on particles transport and concentration. Direct numerical simulations combined with point particle Lagrangian tracking are performed for several geometries such as a pipe, channel, square duct, and squircle (rounded-corners duct). In non-circular ducts, anisotropic and inhomogeneous Reynolds stresses are the most influential phenomena that produce the secondary flows. It has been shown that these motions can have a significant impact on transporting momentum, vorticity, and energy from the core of the duct to the corners. The main focus of the present study is to explore the effects of near the wall structures and secondary flows on turbophoresis, lift, and particle concentration. [Preview Abstract] |
Tuesday, November 22, 2016 8:39AM - 8:52AM |
M28.00004: Stochastic modeling of fluid-particle flows in homogeneous cluster-induced turbulence Alessio Innocenti, Sergio Chibbaro, Rodney Fox, Maria Vittoria Salvetti Inertial particles in turbulent flows are characterized by preferential concentration and segregation and, at sufficient mass loading, dense clusters may spontaneously generate due to momentum coupling between the phases. These clusters in turn can generate and sustain turbulence in the fluid phase, which we refer to as cluster-induced turbulence (CIT). In the present work, we tackle the problem of homogeneous gravity driven CIT in the framework of a stochastic model, based on a Lagrangian formalism which includes naturally the Eulerian one. A rigorous formalism has been put forward focusing in particular on the terms responsible of the two-way coupling in the carrier phase, which is the key mechanism in this type of flow. Moreover, the decomposition of the particle-phase velocity into the spatially correlated and uncorrelated components has been used allowing to identify the contributions to the correlated fluctuating energy and to the granular temperature. Tests have been performed taking into account also the effects of collisions between particles. Results are compared against DNS, and they show a good accuracy in predicting first and second order moments of particle velocity and fluid velocity seen by particles. [Preview Abstract] |
Tuesday, November 22, 2016 8:52AM - 9:05AM |
M28.00005: Modeling particle-laden turbulent flows with two-way coupling using a high-order kernel density function method Timothy Smith, Xiaoyi Lu, Reetesh Ranjan, Carlos Pantano We describe a two-way coupled turbulent dispersed flow computational model using a high-order kernel density function (KDF) method. The carrier-phase solution is obtained using a high-order spatial and temporal incompressible Navier-Stokes solver while the KDF dispersed-phase solver uses the high-order Legendre WENO method. The computational approach is used to model carrier-phase turbulence modulation by the dispersed phase, and particle dispersion by turbulence as a function of momentum coupling strength (particle loading) and number of KDF basis functions. The use of several KDF's allows the model to capture statistical effects of particle trajectory crossing to high degree. Details of the numerical implementation and the coupling between the incompressible flow and dispersed-phase solvers will be discussed, and results at a range of Reynolds numbers will be presented. [Preview Abstract] |
Tuesday, November 22, 2016 9:05AM - 9:18AM |
M28.00006: Particle dynamics during the transition from isotropic to anisotropic turbulence Chung-min Lee, Armann Gylfason, Federico Toschi Turbulent fluctuations play an important role on the dynamics of particles in turbulence, enhancing their dispersion and mixing. In recent years the statistical properties of particles in several statistically stationary turbulent flows have been the subject of many numerical and experimental studies. In many natural and industrial environments, however, one deals with turbulence in a transient state. As a prototype system, we investigate the transition from an isotropic to an anisotropic flow, namely looking at the influence of a developing mean flow on the dynamics of particles. We simulate, via direct numerical simulation, stationary homogeneous and isotropic turbulence and then suddenly impose a mean shear or strain. This allows us to quantify the effects of the mean flow on particle dynamics in these transient periods. Preliminary results on single particle properties, such as velocities and accelerations will be reported. [Preview Abstract] |
Tuesday, November 22, 2016 9:18AM - 9:31AM |
M28.00007: Modification of particle-laden horizontal channel turbulence Junghoon Lee, Changhoon Lee Modification of channel turbulence by small, heavy particles that settle towards the bottom wall under the influence of gravity, interacting with the turbulence is investigated using direct numerical simulations coupled with Lagrangian particle tracking. Particles' momentum transfer to the fluid is implemented via a point-force approximation, and particle-particle interactions are not taken into account in the simulation assuming a dilute suspension. Once a particle reaches the bottom wall, it is removed, and then a new particle is injected at a random location in the very vicinity of the top wall with the vertical terminal velocity and horizontal fluid velocities at the new position, with a focus on particles-turbulence interaction before their deposition. We compare our simulation with the available experimental data to validate the simulation condition used. We discuss modifications of turbulence statistics and coherent structures for various Stokes numbers and identify the role of gravity in the particles-turbulence interaction. Plausible physical mechanisms responsible for the modification behavior are also provided. [Preview Abstract] |
(Author Not Attending)
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M28.00008: Direct numerical simulation of particles in a turbulent channel flow Ankit Tyagi, Vishwanathan Kumaran Goswami and Kumaran(2009a,b,2011a) studied the effect of fluid turbulence on particle phase in DNS.However,their studies were restricted to one way coupling where the effect of particles on fluid turbulence was not incorporated. We have extended their work by formulating a reverse force treatment through multipole expansion for the particle disturbance to the fluid turbulence.Here,the fluid velocity, strain rate and rotation rate at the particle position are used,as a far field,to calculate the disturbance caused by the particle and relaxing the point particle approximation.The simulations are done at high Stokes number where the fluid velocity fluctuations are uncorrelated over time scales of the particle dynamics.The results indicate that the particle mean velocity and stress are reduced when reverse force is incorporated.Level of reduction increases with mass loading and Stokes number.The variance of particle distribution function is reduced due to reduction in the fluid turbulent intensities.The particle velocity,angular velocity distribution function and stresses are compared for simulations where only the reverse force is incorporated, and where the dipoles are also incorporated, to examine the effect of force dipoles on the fluid turbulence and the particle distributions. [Preview Abstract] |
Tuesday, November 22, 2016 9:44AM - 9:57AM |
M28.00009: DNS-DEM of Suspended Sediment Particles in an Open Channel Flow Pedram Pakseresht, Sourabh Apte, Justin Finn DNS with point-particle based discrete element model (DEM) is used to study particle-turbulence interactions in an open channel flow at $Re_{\tau}$ of $710$, corresponding to the experimental observations of Righetti \& Romano (JFM, 2004). Large particles of diameter $200$ microns (10 in wall units) with volume loading on the order of $10^{-3}$ are simulated using four-way coupling with closure models for drag, added mass, lift, pressure, and inter-particle collision forces. The point-particle model is able to accurately capture the effect of particles on the fluid flow in the outer layer. However, the particle is significantly larger than the wall-normal grid in the near-wall region, but slightly smaller than the axial and longitudinal grid resolutions. The point-particle model fails to capture the interactions in the near-wall region. In order to improve the near-wall predictions, particles are represented by Lagrangian material points which are used to perform interpolations from the grid to the Lagrangian points and to distribute the two-way coupling force to the Eulerian grid. Predictions using this approach is compared with the experimental data to evaluate its effectiveness. [Preview Abstract] |
Tuesday, November 22, 2016 9:57AM - 10:10AM |
M28.00010: Particle-turbulence-acoustic interactions in high-speed free-shear flows Gregory Shallcross, David Buchta, Jesse Capecelatro Experimental studies have shown that the injection of micro-water droplets in turbulent flows can be used to reduce the intensity of near-field pressure fluctuations. In this study, direct numerical simulation (DNS) is used to evaluate the effects of particle-turbulence-acoustic coupling for the first time. Simulations of temporally developing mixing layers are conducted for a range of Mach numbers and mass loadings. Once the turbulence reaches a self-similar state, the air-density shear layer is seeded with a random distribution of mono disperse water-density droplets. For M$=$0.9 to M$=$1.75, preliminary results show reductions in the near-field pressure fluctuations for moderate mass loadings, consistent with experimental studies under similar conditions. At high speed, the principle reduction of the normal velocity fluctuations, which increases with particle mass loading, appears to correlate to the reduction of the near-field radiated pressure fluctuations. These findings demonstrate that the DNS reproduces the observed particle-turbulence-acoustic phenomenology, and its complete space--time database can be used to further understand their interactions. [Preview Abstract] |
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