Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session L2: Particle-Laden Flows: Turbulence-Particle Interactions |
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Chair: Michael Reeks, University of Newcastle Room: 101 |
Monday, November 23, 2015 4:05PM - 4:18PM |
L2.00001: A simple stochastic quadrant model for the transport and deposition of particles in turbulent boundary layers Michael Reeks, Chunyu Jin, Ian Potts We present a simple stochastic quadrant model for calculating the transport and deposition of heavy particles in a fully developed turbulent boundary layer based on the statistics of wall-normal fluid velocity fluctuations obtained from a fully developed channel flow. Individual particles are tracked through the boundary layer via their interactions with a succession of random eddies found in each of the quadrants of the fluid Reynolds shear stress domain in a homogeneous Markov chain process. Deposition rates for a range of heavy particles predicted by the model compare well with benchmark experimental measurements. In addition deposition rates are compared with those obtained continuous random walk (CRW) models including those based on the Langevin equation for the turbulent fluctuations. In addition, various statistics related to the particle near wall behavior are also presented. [Preview Abstract] |
Monday, November 23, 2015 4:18PM - 4:31PM |
L2.00002: Neutral and inertial particle acceleration in non isotropic turbulent flows Armann Gylfason, Michel van Hinsberg, Chung-Min Lee, Federico Toschi Turbulent fluctuations influence the dynamics of particulate matter by accelerating the dispersions and mixing of particles. In several natural and industrial flows turbulent fluctuations are strongly coupled to the presence of intense and anisotropic mean flows. The flows that we study here are homogeneous shear and homogeneous strain turbulence. In these flows the dispersion of particles is strongly influenced by gradients in the mean velocity. A comparison of single particle properties, such as acceleration and velocity variances, and time correlations are presented to illustrate the particle dynamics under such conditions. [Preview Abstract] |
Monday, November 23, 2015 4:31PM - 4:44PM |
L2.00003: Neutral and inertial particle acceleration in strained turbulence Chung-min Lee, Armann Gylfason, Prasad Perlekar, Federico Toschi Turbulence influences the transport and mixing of particles. We study the dynamics of particles in turbulent flows undergoing asymmetrically expanding straining by means of direct numerical simulations. We investigate the accelerations of tracer and inertial particles. We find a good agreement between tracer acceleration variance and the prediction of rapid distortion theory. Furthermore we study how particle acceleration probability density functions depend on the strain rate, the Stokes number, and the Reynolds number. Accelerations variances of inertial particles are discussed in the context of the formal solution of the equation of particle motion, and we show that in strong straining the acceleration variance of particles with small Stokes numbers can exceed that of tracer particles. [Preview Abstract] |
Monday, November 23, 2015 4:44PM - 4:57PM |
L2.00004: Settling of almost neutrally buoyant particles in homogeneous isotropic turbulence Michel van Hinsberg, Herman Clercx, Federico Toschi Settling of particles in a turbulent flow occurs in various industrial and natural phenomena, examples are clouds and waste water treatment. It is well known that turbulence can enhance the settling velocity of particles. Many studies have been done, numerically and experimentally to investigate this behavior for the case of ’heavy’ particles, with particle to fluid density ratios above 100. Here we investigate the case of almost neutrally buoyant particles, i.e. density ratios between 1 and 100. In the case of light particles the Maxey-Riley equations cannot be simplified to only the Stokes drag and gravity force as pressure gradient, added mass and Basset history force are important as well. We investigate the influence of these forces on the settling velocity of particles and show that the extra forces can both increase or decrease the settling velocity, depending on the combination of the Stokes number and gravity applied. [Preview Abstract] |
Monday, November 23, 2015 4:57PM - 5:10PM |
L2.00005: Collision statistics of inertial particles suspended in turbulent flows of low dissipation rates Sandipan Banerjee, Orlando Ayala, Lian-Ping Wang The collision rate of sedimenting droplets in turbulent flows is of great importance in cloud physics. Parameters like the collision efficiency and collision enhancement are key inputs for the calculation of growth in the size of the cloud droplets due to coalescence. In this presentation we report the collision statistics of particles in turbulent flows of low dissipation rates (in the range of 3 cm$^2$/sec$^3$-100 cm$^2$/sec$^3$) for three different particle-pair sizes. Due to the expensive nature of the simulations, it is a common practice to use the linear interpolation to estimate the collision efficiency enhancement (which is defined as the ratio of the collision efficiency in a turbulent flow to the collision efficiency without the flow). In this study, along with the collision statistics, we also examine the accuracy of the linear interpolation approximation by comparing it to simulation data, at arbitrary dissipation rates, obtained from a hybrid direct numerical simulation. Furthermore, we also report particle pair statistics such as the particle relative velocity and the radial distribution function. A study on the computational cost of the simulations is also included. [Preview Abstract] |
Monday, November 23, 2015 5:10PM - 5:23PM |
L2.00006: A Subgrid Particle Averaged Reynolds Stress Equivalent (SPARSE) model for Eulerian-Lagrangian particle-laden-flow simulation Sean Davis, Gustaaf Jacobs The direct Eulerian-Lagrangian simulation of turbulent, particle-laden flow through the Navier-Stokes equations combined with the tracing of a large number of particles is computationally expensive for large-scale problems. To reduce computational cost, small scale turbulence is often modeled and groups of physical particles are amalgamated into clouds, whose average location is traced. Typical Lagrangian models (such as Particle-Source-In-Cell and Cloud-In-Cell models) assume that the average motion of the cloud is governed by only the average interphase momentum difference between the carrier and disperse phases, neglecting subscale perturbations. We present a new Lagrangian particle model for the tracing of clouds of particles in particle-laden flows. By expanding the particle drag correction factor to include fluctuating terms and Reynolds averaging the full particle momentum equation, the so-called SPARSE model accounts for the effect of subgrid turbulence and particle perturbations. A priori results demonstrate the efficacy of the SPARSE model in 1D velocity fields and 3D decaying isotropic turbulence computations.~ [Preview Abstract] |
Monday, November 23, 2015 5:23PM - 5:36PM |
L2.00007: Accelerated Stochastic Vortex Structure Method for Transport of Interacting Particles in Turbulent Flow Jeffrey Marshall, Kyle Sala, Farzad Dizaji Turbulent particle transport with RANS or LES methods typically requires an additional model for effect of subgrid-scale eddies on the particles. For non-interacting particles stochastic Lagrangian methods are widely used for this purpose, but these models yield poor results for interacting particles due to lack of spatial correlation in the random forcing terms. Traditional synthetic turbulence methods used for LES initial conditions are often too slow to be useful for particle transport, and they usually lack the vortex structures which are important for generation of particle clustering. In the current work, an accelerated stochastic vortex structure (SVS) method is proposed for generation of synthetic turbulence for transport of interacting particles. The SVS model is shown to yield flow measures, such as energy spectrum and velocity, acceleration and vorticity pdfs, in good agreement with DNS results and with relevant theory. When coupled to a discrete-element method (DEM) code for particle transport, the SVS model is observed to yield very accurate results for particle collision rate and other measures of particle interaction. [Preview Abstract] |
Monday, November 23, 2015 5:36PM - 5:49PM |
L2.00008: Euler-Euler anisotropic Gaussian mesoscale direct numerical simulation of homogeneous and wall-bounded cluster-induce gas-particle turbulence Bo Kong, Heng Feng, Jesse Capecelatro, Olivier Desjardins, Rodney Fox In our previous works,the exact Reynolds-averaged equations for the particle phase were derived to develop a new mutilphase turbulence model with a rigorous conceptual foundation, and detailed Euler-Lagrange(EL) particle simulations of cluster-induced turbulence (CIT) were performed to aid its development. However, sophisticated filtering techniques have to be used to extract Eulerian particle-phase statistics from the EL simulations, which can be directly provided by Euler-Euler approaches. In this work, a novel Euler-Euler anisotropic Gaussian (AG) approach was used to perform mesoscale DNS of the CIT cases. A three-dimension Hermite Quadrature formulation is used to calculate finite-volume kinetic flux for ten velocity moments. Bhatnagar-Gross-Krook model is applied to account for the inelastic particle collisions. Detailed comparisons with EL simulations demonstrate that the AG particle velocity assumption is valid and this novel method can be used to perform mesoscale DNS for gas-particle flows with high fidelity. [Preview Abstract] |
Monday, November 23, 2015 5:49PM - 6:02PM |
L2.00009: A high-order Legendre-WENO kernel density function method for modeling disperse flows Timothy Smith, Carlos Pantano We present a high-order kernel density function (KDF) method for disperse flow. The numerical method used to solve the system of hyperbolic equations utilizes a Roe-like update for equations in non-conservation form. We will present the extension of the low-order method to high order using the Legendre-WENO method and demonstrate the improved capability of the method to predict statistics of disperse flows in an accurate, consistent and efficient manner. By construction, the KDF method already enforced many realizability conditions but others remain. The proposed method also considers these constraints and their performance will be discussed. [Preview Abstract] |
Monday, November 23, 2015 6:02PM - 6:15PM |
L2.00010: A novel particle SGS model based on differential filter for LES of particle-laden turbulent flows George Park, Javier Urzay, Parviz Moin When performing LES of particle-turbulence interactions, proper modelling of the effect of subgrid-scale (SGS) fluid motions on the particle dynamics is critical for accurate prediction of particle dispersion. Existing particle SGS models recover the missing SGS fluid velocities required in the particle equation of motion by assuming stochastic evolution of SGS fluctuations seen by particles, or by deconvolving the LES solution with an approximate inverse of the filter. In this study, we investigate the use of the differential filter for deconvolution-based particle SGS modelling. Deconvolution with a differential filter is potentially an attractive alternative to the existing Pade-filter based approximate deconvolution techniques. Exact deconvolution can be done trivially with differential filter, because the filter is defined in the inverse-filter form, and the method can be easily extended to unstructured grids. LES of one-way coupled particle-turbulence interaction in isotropic turbulence is performed, and model performance is analysed in terms of particle dispersion statistics. A dynamic procedure for determining the coefficient related to the filter width is under development, and the resulting formulation will be compared to constant coefficient models. [Preview Abstract] |
Monday, November 23, 2015 6:15PM - 6:28PM |
L2.00011: Dynamics of kinetic energy transfer in homogeneous bidisperse gas-solid flow using particle-resolved direct numerical simulation Mohammad Mehrabadi, Shankar Subramaniam While considerable insight has been gained into the dynamics of energy transfer in monodisperse gas-solid flows, much less is known about polydisperse systems where particles have a size distribution. For instance, the conservation of interphase turbulent kinetic energy transfer (ITKET) principle for monodisperse gas-solid flow (Xu and Subramaniam, Phys. Fluids, 2007) states that the power provided by the mean pressure gradient to sustain a mean slip velocity between the fluid phase and solid phase is equal to the mixture ITKET of the suspension, which is then partitioned into sources of velocity fluctuations in the gas and solid phases. As a first step towards understanding the dynamics of energy transfer in polydisperse suspensions, we analyze the extension of this conservation principle to a bidisperse suspension. Here the mixture ITKET is partitioned into sources of velocity fluctuations of the fluid phase as well as the large and small particle size classes. PR-DNS results of homogeneous bidisperse gas-solid flow are then used to verify this extended conservation principle. With these insights we can begin to answer interesting questions such as the role of energy transfer in promoting segregation or mixing of particle sizes. [Preview Abstract] |
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