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 E33: Turbulence: Particle-laden Flows |
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Chair: Perry Johnson, Johns Hopkins University Room: Oregon Ballroom 202 |
Sunday, November 20, 2016 5:37PM - 5:50PM |
E33.00001: Restricted Euler dynamics along trajectories of small inertial particles in turbulence Perry Johnson, Charles Meneveau The fate of small particles in turbulent flows depends strongly on the surrounding fluid's velocity gradient properties such as rotation and strain-rates. For non-inertial (fluid) particles, the Restricted Euler model provides a simple, low-dimensional dynamical system representation of Lagrangian evolution of velocity gradients in fluid turbulence, at least for short times. Here we derive a new restricted Euler dynamical system for the velocity gradient evolution of inertial particles such as solid particles in a gas or droplets and bubbles in turbulent liquid flows. The model is derived in the limit of small (sub Kolmogorov scale) particles and low Stokes number. The system exhibits interesting fixed points, stability and invariant properties. Comparisons with data from Direct Numerical Simulations show that the model predicts realistic trends such as the tendency of increased straining over rotation along heavy particle trajectories and, for light particles such as bubbles, the tendency of severely reduced self-stretching of strain-rate. [Preview Abstract] |
Sunday, November 20, 2016 5:50PM - 6:03PM |
E33.00002: Simulation of finite size particles in turbulent flows using entropic lattice boltzmann method Abhineet Gupta, Herman J. H. Clercx, Federico Toschi Particle-laden turbulent flows occur in variety of industrial applications. While the numerical simulation of such flows has seen significant advances in recent years, it still remains a challenging problem. Many studies investigated the rheology of dense suspensions in laminar flows as well as the dynamics of point-particles in turbulence. Here we will present results on the development of numerical methods, based on the Lattice Boltzmann method, suitable for the study of suspensions of finite-size particles under turbulent flow conditions and with varying geometrical complexity. The turbulent flow is modeled by an entropic lattice Boltzmann method, and the interaction between particles and carrier fluid is modeled using bounce back rule. Direct contact and lubrication force models for particle-particle interactions and particle-wall interaction are taken into account to allow for a full four-way coupled interaction. The accuracy and robustness of the method is discussed by validating velocity profile in turbulent pipe flow, sedimentation velocity of spheres in duct flow and resistance functions of approaching particles. Results show that the velocity profiles and turbulence statistics can be significantly altered by the presence of the dispersed solid phase. [Preview Abstract] |
Sunday, November 20, 2016 6:03PM - 6:16PM |
E33.00003: Multiscale geometrical Lagrangian statistics: scale-dependent curvature and torsion angles in particle-laden turbulent flows Kai Schneider, Benjamin Kadoch, Maxime Bassenne, Mahdi Esmaily-Moghadam, Marie Farge, Wouter Bos We present multiscale statistics of particle trajectories in isotropic turbulence and compare the behaviour of fluid and inertial particles. The directional change of inertial particles is quantified by considering the curvature angle for different time increments. Distinct scaling behaviors of the mean angle are observed for short, intermediate and long time lags. We also introduce the scale-dependent torsion angle, which quantifies the directional change of particles moving out of the plane. The influence of the Stokes and Reynolds numbers on the mean angles and on the probability distributions are analyzed. Finally, we assess the impact of LES and particle SGS modeling on those statistics. [Preview Abstract] |
Sunday, November 20, 2016 6:16PM - 6:29PM |
E33.00004: Effect of particle inertia on fluid turbulence in gas-solid disperse flow Yoichi Mito The effect of particle inertia on the fluid turbulence in gas-solid disperse flow through a vertical channel has been examined by using a direct numerical simulation, to calculate the gas velocities seen by the particles, and a simplified non-stationary flow model, in which a uniform distribution of solid spheres of density ratio of 1000 are added into the fully-developed turbulent gas flow in an infinitely wide channel. The gas flow is driven downward with a constant pressure gradient. The frictional Reynolds number defined with the frictional velocity before the addition of particles, $v_0^*$, is 150. The feedback forces are calculated using a point force method. Particle diameters of 0.95, 1.3 and 1.9, which are made dimensionless with $v_0^*$ and the kinematic viscosity, and volume fractions, ranging from $1 \times 10^{-4}$ to $2 \times 10^{-3}$, in addition to the one-way coupling cases, are considered. Gravitational effect is not clearly seen where the fluid turbulence is damped by feedback effect. Gas flow rate increases with the decrease in particle inertia, that causes the increase in feedback force. Fluid turbulence decreases with the increase in particle inertia, that causes the increase in diffusivity of feedback force and of fluid turbulence. [Preview Abstract] |
Sunday, November 20, 2016 6:29PM - 6:42PM |
E33.00005: Statistics of relative velocities of heavy particles in turbulence Dhrubaditya MITRA, Akshay Bhatnagar, Kristian Gustafsson, Bernhard Mehlig We consider heavy, inertial, passive, particles in homogeneous and isotropic turbulent flows. Using direct numerical simulations we study the statistics of relatives velocities of identical particles. We calculate the $p^{\rm th}$ order moments $m_{\rm p}(R)$ of the collision velocity as a function of particle size. We find that, in agreement with theory, the moments show bifractal scaling behavior confirming the effects of caustics. We also compute the joint probability distribution functions (PDFs) of relative velocity and separation between two closeby particles and compare with theory at intermediate and large Stokes numbers. [Preview Abstract] |
Sunday, November 20, 2016 6:42PM - 6:55PM |
E33.00006: How long do particles spend in vortical regions in turbulent flows? Akshay Bhatnagar, Anupam Gupta, Dhrubaditya Mitra, Rahul Pandit, Prasad Perlekar We consider passive, heavy, inertial, particles (HIP) in three-dimensional, homogeneous, and isotropic turbulence. Whether a particle is in a vortical regions or not is determined by the two invariants of the (flow) velocity gradient matrix , $Q$ and $R$, at the position of the parti cle. Using direct numerical simulations, we calculate the probability distribution functions (PDFs) of the first-passage-time of a tracer or a HIP in a vortical region. The corresponding PDF in two dimensions is known to show power-law tail. In three dimensions we find that the PDF possesses exponential tail with a characteristic time of the order of large-eddy-turnover-time of the flow. [Preview Abstract] |
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