Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session G32: Particle-Laden Flows: Particle-Turbulence Interaction |
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Chair: Rodney O. Fox, Iowa State University Room: 2020 |
Monday, November 24, 2014 8:00AM - 8:13AM |
G32.00001: Laminar-turbulent transition and inertial shear-thickening of particle suspensions Luca Brandt, Iman Lashgari, Francesco Picano, Wim-Paul Breugem When a suspension of rigid particles is considered instead of a pure fluid, the particle-fluid interactions significantly alter the bulk behavior of the flow unexplained effects appear in the transitional regime. These are important in several environmental and industrial applications. The aim of this study is to characterize the flow regimes of suspensions of finite-size rigid particles in a viscous fluid at finite inertia. We explore the system behavior as function of the particle volume fraction and the Reynolds number. Unlike single phase flows where a clear distinction exists between the laminar and the turbulent states, three different regimes can be identified in the presence of a particulate phase, with smooth transitions between them. At low volume fractions, the flow becomes turbulent when increasing the Reynolds number, transitioning from the laminar regime dominated by viscous forces to the turbulent regime characterized by enhanced momentum transport by turbulent eddies. At larger volume fractions, we identify a new regime characterized by an even larger increase of the wall friction. The wall friction increases with the Reynolds number (inertial effects) while the turbulent transport is unaffected, as in a state of intense inertial shear-thickening. [Preview Abstract] |
Monday, November 24, 2014 8:13AM - 8:26AM |
G32.00002: Multiphase turbulence in vertical wall-bounded collisional gas-particle flows Rodney O. Fox, Jesse Capecelatro, Olivier Desjardins Wall-bounded particle-laden flows are common in many environmental and industrial applications, and are often turbulent. In vertical flows, strong coupling between the phases leads to the spontaneous generation of dense clusters that fall due to gravity at the walls, while dilute suspensions of particles rise in the central region. Sustained volume fraction and velocity fluctuations caused by the clusters result in the production of fluid-phase turbulent kinetic energy, referred to as cluster-induced turbulence (CIT). To better understand the nature of CIT in wall-bounded flows, Eulerian-Lagrangian simulations of statistically stationary three-dimensional gas-solid flows in vertical pipes are performed. To extract useful information consistent with Eulerian turbulence models, a separation of length scales is introduced to decompose correlated and uncorrelated granular motion. To accomplish this, an adaptive spatial filter is employed on the particle data with an averaging volume that varies with the local particle-phase volume fraction. Radial profiles of turbulence statistics are generated from the Eulerian-Lagrangian results. Details on the nature of the turbulence are described, as well as the challenges they present to turbulence modeling. [Preview Abstract] |
Monday, November 24, 2014 8:26AM - 8:39AM |
G32.00003: Ineractions of Turbulence and Sediment Particles in an Open Channel Flow Pedram Pakseresht, Sourabh Apte, Justin Finn Interactions of glass particles in water in a turbulent open channel flow over a smooth bed is examined using direct numerical simulation (DNS) together with Lagrangian Discrete-Element-Model (DEM) for particles. Unlike several studies on wall-bounded turbulent flows with particles, in this work, the gravity is perpendicular to the mean flow, resulting in interesting dynamics between the destabilizing lift forces on the particles and stabilizing effects of graivty. The turbulent Reynolds number ($Re_{\tau}$) is $710$ corresponding to the experimental observations of Righetti \& Romano (JFM, 2004). Particles of size $100$ microns with volume loading of $10^{-3}$ result in a single layer of non-touching particles at the bottom wall. The entrainment and deposition mechanisms of particles and their interactions with the near wall turbulence structure are studied in detail. For the particle concentration studied, the particles affect the flow field in both the outer as well as inner region of the wall layer where particle inertia and concentration are higher. The effect of these interactions on the wall events is being explored. [Preview Abstract] |
Monday, November 24, 2014 8:39AM - 8:52AM |
G32.00004: Fluid-particle characteristics in fully-developed cluster-induced turbulence Jesse Capecelatro, Olivier Desjardins, Rodney Fox In this study, we present a theoretical framework for collisional fluid-particle turbulence. To identify the key mechanisms responsible for energy exchange between the two phases, an Eulerian-Lagrangian strategy is used to simulate fully-developed cluster-inudced turbulence (CIT) under a range of Reynolds numbers, where fluctuations in particle concentration generate and sustain the carrier-phase turbulence. Using a novel filtering approach, a length-scale separation between the correlated particle velocity and uncorrelated granular temperature (GT) is achieved. This separation allows us to extract the instantaneous Eulerian volume fraction, velocity and GT fields from the Lagrangian data. Direct comparisons can thus be made with the relevant terms that appear in the multiphase turbulence model. It is shown that the granular pressure is highly anisotropic, and thus additional transport equations (as opposed to a single equation for GT) are necessary in formulating a predictive multiphase turbulence model. In addition to reporting the relevant contributions to the Reynolds stresses of each phase, two-point statistics, integral length/timescales, averages conditioned on the local volume fraction, and PDFs of the key multiphase statistics are presented and discussed. [Preview Abstract] |
Monday, November 24, 2014 8:52AM - 9:05AM |
G32.00005: ABSTRACT WITHDRAWN |
Monday, November 24, 2014 9:05AM - 9:18AM |
G32.00006: The effect of the dissipation of energy on the hydrodynamics of the gas-particle fluidized beds D.J. Bergstrom, Mohammad Reza Haghgoo, R.J. Spiteri The flow structure in dense gas-particle fluidized beds is strongly affected by the dissipation of kinetic energy through particle collisions with each other and the wall. The energy dissipation reduces the kinetic energy of the particles. Consequently, larger clusters will be formed, and this in turn leads to the formation of larger bubbles. Therefore, it is insightful to investigate the instantaneous dissipation of energy in a fluidized bed in order to have a better understanding of the hydrodynamics of the particle phase. Visualization of the dissipation term will also clarify how much the walls contribute to the dissipation of energy in the overall system. In this study, a two-fluid model is used for the numerical simulation of an engineering-scale bubbling fluidized bed. The MFiX code is used to perform the simulations. A modified SIMPLE algorithm for multiphase flows is employed that uses a higher-order discretization scheme to accurately compute bubble shapes and the deferred correction method to enhance numerical stability. The results of the three-dimensional simulation are in good agreement with the limited experimental data. The dissipation of the kinetic energy of the particles is evaluated using the model relations based on the simulated particle velocity fields. [Preview Abstract] |
Monday, November 24, 2014 9:18AM - 9:31AM |
G32.00007: Lagrangian statistics of inertial particles in near-wall turbulence Junghoon Lee, Changhoon Lee Despite many studies regarding particle-laden turbulence in near-wall turbulence, detailed investigation on the Lagrangian nature of particles is very rare. In our study, inertial particle trajectories suspended in turbulent channel flow were calculated via direct numerical simulation with Lagrangian particle tracking. Since particles smaller than the Kolmogorov length scale and their dilute suspension are addressed in this study, one-way coupled simulations with point-particle approach are performed. By ensemble-averaging over a number of particles, we investigate Lagrangian statistics, such as particle dispersion, velocity and acceleration autocorrelation and probability density function of expected particle position, of particles released at several different distances from the wall for a wide range of Stokes numbers. In addition, the effects of gravity and lift on the Lagrangian statistics are investigated. Plausible physical explanations are provided. [Preview Abstract] |
Monday, November 24, 2014 9:31AM - 9:44AM |
G32.00008: Rotational response of suspended particles to turbulent flow: laboratory and numerical synthesis Evan Variano, Lihao Zhao, Margaret Byron, Gabriele Bellani, Yiheng Tao, Helge Andersson Using laboratory and DNS measurements, we consider how aspherical and inertial particles suspended in a turbulent flow act to ``filter'' the fluid-phase vorticity. We use three approaches to predict the magnitude and structure of this filter. The first approach is based on Buckingham's Pi theorem, which shows a clear result for the relationship between filter strength and particle aspect ratio. Results are less clear for the dependence of filter strength on Stokes number; we briefly discuss some issues in the proper definition of Stokes number for use in this context. The second approach to predicting filter strength is based on a consideration of vorticity and enstrophy spectra in the fluid phase. This method has a useful feature: it can be used to predict the filter a priori, without need for measurements as input. We compare the results of this approach to measurements as a method of validation. The third and final approach to predicting filter strength is from the consideration of torques experienced by particles, and how the ``angular slip'' or ``spin slip'' evolves in an unsteady flow. We show results from our DNS that indicate different flow conditions in which the spin slip is more or less important in setting the particle rotation dynamics. [Preview Abstract] |
Monday, November 24, 2014 9:44AM - 9:57AM |
G32.00009: Three Dimensional Tracking of Two-Particle Dispersion in a Turbulent Jet Stephanie Paustian, Chin Hei Ng, Alberto Aliseda We present experimental measurements of two-particle dispersion in a turbulent shear flow. The baseline flow is a well-characterized high Reynolds number (up to approximately 200,000) turbulent submerged round jet. Injection is performed in the self-similar part of the jet, where careful PIV measurements of the mean flow field and turbulent second order moments have been obtained and validated against theory and other experiments. Three-dimensional tracking of two particles, injected simultaneously at two different radial or axial positions in the jet, is obtained from two-camera high-speed shadowgraphy. The influence of mean shear and turbulence fluctuations on dispersion is analyzed for initial positions where a mean velocity shear is superimposed on turbulent fluctuations. Injection of different particles, liquid droplets and gas bubbles is performed to analyze the influence of density ratio, particle inertia and buoyancy on the dispersion ratio. The versatility of the experimental facility also allows for the experimental investigation of the Reynolds number effect on dispersion, ranging from below the mixing transition (approximately 3,000) to very high values (\textgreater 100,000). [Preview Abstract] |
Monday, November 24, 2014 9:57AM - 10:10AM |
G32.00010: Application of Medical Magnetic Resonance Imaging for Particle Concentration Measurement Daniel Borup, Christopher Elkins, John Eaton Particle transport and deposition in internal flows is important in a range of applications such as dust aggregation in turbine engines and aerosolized medicine deposition in human airways. Unlike optical techniques, Magnetic Resonance Imaging (MRI) is well suited for complex applications in which optical access is not possible. Here we present efforts to measure 3D particle concentration distribution using MRI. Glass particles dispersed in water flow reduce MRI signal from a spin-echo or gradient-echo scanning sequence by decreasing spin density and dephasing the spins present in the fluid. A preliminary experiment was conducted with a particle streak injected at the centerline of a turbulent round pipe flow with a U bend. Measurements confirmed that signal strength was related to particle concentration and showed the effects of gravitational settling and turbulent dispersion. Next, measurements of samples in a mixing chamber were taken. Particle volume fraction was varied and sensitivity to particle/fluid velocity was investigated. These results give a relationship between MRI signal, particle volume fraction, MRI sequence echo time, and spin relaxation parameters that can be used to measure local particle volume fraction in other turbulent flows of interest. [Preview Abstract] |
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