Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session Q37: Particle-Laden Flows: Homogeneous and Wall Flows |
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Chair: Jasse Capecelatro, University of Michigan Room: Georgia World Congress Center B409 |
Tuesday, November 20, 2018 12:50PM - 1:03PM |
Q37.00001: Modulation of turbulence by stationary multiple-particle Mohammad Mainul Hoque, Subhasish Mitra, Geoffrey Evans Modulation of turbulent flow in an oscillating grid system due to the presence of stationary multiple particles was experimentally investigated using particle image velocimetry (PIV) technique wherein flow field modulation was reported in particle resolved manner. The particle diameter varied in the range ~ 3 to 7 mm (~ 30 to 68 times the single-phase Kolmogorov scale). The PIV velocity fields were obtained at grid Reynolds numbers (Reg) ranging from 1080 to 10800. The single-phase turbulence fluctuating velocity increased in the inertial subrange region due to the presence of particles. Presence of particles led to enhancement in the flow field isotropy ratio which is completely opposite compared to the results of stationary single-particle case reported in Hoque et al. (2016). The energy spectra exhibited a slope less steep than −5/3 in the presence of particles which indicates the additional turbulence production by the particles in the inertial subrange region. Energy augmentation from large scale to small scale due to particles were discussed by the dissipative spectrum which showed that a reduction of the energy on the small scale and an enhancement of the energy on both large scale and inertial subrange. |
Tuesday, November 20, 2018 1:03PM - 1:16PM |
Q37.00002: Experimental study of turbulent flow of spherical particles in Newtonian and drag reducing viscoelastic fluid. Sagar Zade, Fredrik Lundell, Luca Brandt Particle image velocimetry in suspensions of large inertial spherical particles in Newtonian as well as drag reducing viscoelastic fluid is performed using refractive index-matched particles. Two geometries are investigated: a horizontal square duct and a round pipe. For the square duct, turbulent flow statistics, pressure drop, and particle concentration distribution are measured at a bulk Reynolds number Re of 11000. The particles are nearly neutrally-buoyant and the duct height to particle diameter ratio is 10. The volume fraction Φ is varied between 0-20%. Addition of particles causes a monotonic increase in the pressure drop with concentration. However, the rate of increase is faster in viscoelastic fluid. The Reynolds shear stress decreases with increasing Φ, more for viscoelastic fluid. Similar to Newtonian fluid, particles migrate towards the core as well as towards the wall. For the round pipe, only pressure drop is measured for a range of Re from 5000 to 35000 for three particle sizes: D/dp = 43, 21 and 10. For all cases, increasing Φ and size leads to increased pressure drop. At high Re and high Φ, the largest particles cause an abrupt increase in drag, a feature similar to Newtonian flow.
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Tuesday, November 20, 2018 1:16PM - 1:29PM |
Q37.00003: Modulation of the turbulence regeneration cycle by inertial particles in planar Couette flow Guiquan Wang, David H Richter Two-way coupled direct numerical simulations are used to investigate the effects of inertial particles on self-sustained regeneration cycle in plane Couette flow at low Reynolds number just above the onset of transition. Tests show two limiting behaviors with increasing particle inertia, similar to the results from the linear stability analysis of Saffman (1962): low-inertia particles trigger the laminar-to-turbulent instability whereas high-inertia particles tend to stabilize turbulence due to the extra dissipation induced by particle-fluid coupling. We show that the presence of inertial particles does not alter the periodic nature of the cycle or the relative length of each of the sub-steps. Instead, high-inertia particles greatly weaken the large-scale vortices as well as the streamwise vorticity stretching and lift-up effects, thereby suppressing the fluctuating amplitude of the large scale streaks. The primary influence of low-inertia particles, however, is to strengthen the large scale vortices, which fosters the cycle and ultimately reduces the critical Reynolds number. |
Tuesday, November 20, 2018 1:29PM - 1:42PM |
Q37.00004: Sound and turbulence modulation by particles in high-speed shear flows Gregory Shallcross, David Buchta, Jesse S Capecelatro Direct numerical simulations of particle-laden, high-speed shear layers for Mach numbers varying from 0.9 to 2.5 are used to quantify the effect of inertial particles on turbulence and near-field pressure intensity. Particles are seeded within the shear-layer turbulence with an initial mass loading varying between 0 and 10 and Stokes numbers ranging from 1 to 16. Through the shear layer growth, the near-field pressure levels are observed to change by as much as 5 dB compared to unladen flows. In subsonic flow, the sound level increases with particle loading which is consistent with low-Mach number multiphase aeroacoustic theory. This increase, despite a marked decrease in turbulence level, suggests a non-trivial source-to-sound decomposition. Supersonic flows exhibit a different behavior; sound levels decrease with increase particle loading. Additionally, the sub-Kolmogorov-size particles have a broadband effect on the pressure and turbulence spectra: decreasing energy in large-scale components and vice versa for smaller scales. The volume-filtered compressible flow equations are formulated and averaged to obtain a transport equation for the pressure intensity in the presence of particles, which is used to quantify mechanisms of local turbulence-pressure changes. |
Tuesday, November 20, 2018 1:42PM - 1:55PM |
Q37.00005: Discontinuous transition in turbulence intensity in a particle-laden channel flow Pradeep Muramalla, Ankit Tyagi, Partha S. Goswami, Viswanathan Kumaran Wall bounded particulate systems exhibit various phenomena that can greatly influence the carrier phase due to dispersed phase. In the present work, the turbulence modulation of fluid phase is examined in dilute and moderately dense limit by four-way coupled Direct Numerical Simulation (DNS) in a vertically downward channel using Eulerian - Lagrangian approach. Simulation results are obtained for various Stokes number of particles. It is observed that there is a Critical Particle Volume Loading (CPVL) at which a sharp decay in turbulence intensity occurs and Reynolds stress becomes zero. The CPVL at which such a transition occurs may differ with change in Stokes number. Mean gas velocity profiles also depart from fully developed channel flow at this critical volume loading, with sharp increase at the center of the channel. Since a constant bulk flow condition is maintained, the pressure gradient and wall shear stress are modified due to particle loading. Since the Reynolds stress is zero beyond CPVL, particle feed back force balances the mean pressure gradient and viscous stress term. Mean and Turbulent Kinetic Energy (TKE) budget for different particle loading have been estimated. |
Tuesday, November 20, 2018 1:55PM - 2:08PM |
Q37.00006: A LBM-based Hybrid Method for Simulating Flows with Rigid and Deformable Particles Baili Zhang, Duc-Vinh Le, Ming Cheng, Jing Lou The lattice Boltzmann method (LBM) has been widely used in the study of particulate flows, which have a wide range of applications in fundamental research as well as engineering practice. In this paper, a LBM-based hybrid method is presented for the simulations of resolved particle-laden flows. This method combines the most desirable features of the lattice Boltzmann method and the immersed boundary method by using a regular Eulerian mesh for the flow domain and a Lagrangian mesh for the moving particles in the flow field. The impact of the moving particles to the flow field is considered by introducing a force density term into the framework of lattice Boltzmann method. For the rigid particles, the force density term is simply computed by the concept of momentum exchange at the particle boundary point. While for the deformable particles, a thin-shell model within the framework of the Kirchhoff-Love theory is adopted to compute the forces acting on the shell middle surface during the deformation. This hybrid approach provides a simple and efficient way to treat particle-fluid boundary conditions and is quite suitable for tracking a large group of particles in the flow. The present method will be used to study the particle and cell controls and manipulations in micro-fluidics. |
Tuesday, November 20, 2018 2:08PM - 2:21PM |
Q37.00007: Analysis of carrier phase fluctuations during the passage of a shock wave through a particle cloud Andreas Nygård Osnes, Magnus Vartdal, Bjørn Anders Pettersson Reif
Shock wave interaction with particle clouds of moderate volume fractions generates fluctuations in the carrier phase that are of the order of the mean flow. The majority of effective field models used for such flows neglect these fluctuations, resulting in erroneous bulk flow fields and subsequently erroneous particle distributions. We investigate the nature of these fluctuations using three-dimensional particle resolved LES simulations of shock waves passing through particle clouds, varying incident shock Mach numbers, particle number densities, and volume fractions. The simulations are performed using an entropy stable numerical scheme on a Voronoi background mesh with body fitted structured meshes around each particle. The particles are assumed to be stationary during the simulated time interval. Analysis of the results shows that the dominant fluctuation production term is the product of the forces on the particles and the mean carrier phase velocity. We also observe that the pressure-dilatation correlation is highly correlated with this production term. |
Tuesday, November 20, 2018 2:21PM - 2:34PM |
Q37.00008: A surface-resolved unstructured method for large-scale simulation of particle-laden turbulent flow Wyatt Horne, Krishnan Mahesh Particle-laden flows involve a large range of length scales spanning from large convective scales down to scales near that of individual particles. Resolving the fluid features below that of individual particles presents difficult numerical challenges. We present a method that simulates such cases for many moving particles (O (100,000) particles) using surface-resolved unstructured overset meshes. A dynamic overset assembly is conducted to connect mesh solutions. To establish communication patterns a parallel master/slave algorithm is used. A parallel flood-fill algorithm is used for cutting. For searches, k-d tree data structures are used. Often the connectivity between overset meshes remains the same between time steps. The temporal coherence of objects is directly used to only update necessary information with time, resulting in substantial cost savings. A non-dissipative method is used for the fluid flow. An interpolant is used which has superior kinetic energy properties compared to local reconstructions. To solve pressure, a penalty constraint formulation is used, resulting in a symmetric, positive definite system. Canonical flows are shown. Strong scaling is demonstrated for 100,000 particles in a turbulent channel flow up to 492,000 cores. |
Tuesday, November 20, 2018 2:34PM - 2:47PM |
Q37.00009: Buoyant ellipsoidal particles at high Galileo numbers Martin Assen, Vamsi Spandan, Richard Stevens, Roberto Verzicco, Detlef Lohse Large and buoyant ellipsoidal particles display path instabilities at sufficiently high Galileo numbers due to the break-up of the wake symmetry. Using direct numerical simulations with the immersed boundary method, we analyse the dynamics of a freely rising buoyant particle by varying its aspect ratio over a range of Galileo numbers. The density ratio of the solid particle to the fluid phase is held constant. The study employs a single buoyant particle in an opposing counter flow. For a fixed particle Reynolds number, we set the flow conditions such that the net buoyancy force on the particle balances its drag. We link rising modes to the particles’ Galileo number and analyse the rise velocity for various particle shapes and aspect ratios. |
Tuesday, November 20, 2018 2:47PM - 3:00PM |
Q37.00010: Multi-camera PIV imaging in two-phase flow for improved dispersed-phase concentration and velocity calculation Chang Liu, Ken Kiger Sediment transport from a mobile bed is characterized by large spatial gradients in sediment concentration embedded within a strongly coupled turbulent boundary layer. One of the fundamental open questions of study is how these particle-laden flows modulate the turbulence and the effective stress that is communicated to the outer flow and bed. In the current work, we are interested in advancing quantitative imaging to provide simultaneous high-resolution measures of both phases (sediment and water). In the majority of these conditions, the sediment particles are typically 1-2 orders of magnitude larger than the tracers, which renders the utilization of the most recent developments in tracer particle tracking techniques ineffective (e.g. shake-the-box, MART), as they rely on the assumption of a prescribed simple particle image model. The current work is an extension of prior efforts developing a multi-camera imaging method for extending concentration measurement, incorporating the temporal information for the purpose of resolving the instantaneous velocity of both the dispersed phase and the carrier tracer particles. Finally, the proposed method is employed to an oscillating sheet flow experiment and the phase averaged sediment concentration and flux results are presented. |
Tuesday, November 20, 2018 3:00PM - 3:13PM |
Q37.00011: Numerical and experimental analysis of particle-laden duct flows subject to radiation Laura Villafane, Thomas Jaravel, Andrew Banko, Ji Hoon Kim, John K. Eaton Fluctuations of particle concentration arising from particle-turbulence interaction lead to system characteristics that differ from predictions based on homogeneous concentration distributions. In particle-solar-receivers small and heavy particles advected by a turbulent stream absorb the solar radiation and heat the surrounding gas. Particle clustering gives rise to gas temperature fluctuations and modulates the radiation transmitted across the system. A turbulent square duct laden with inertial particles and exposed to monochromatic radiation through one of the walls is studied computationally and experimentally to gain insights on the coupling between particles, turbulence and radiation. Results are analyzed at various particle loadings for a bulk Reynolds number ReH=20000 and a Stokes number Stk=5. DNS of the gas and point-particle Lagrangian tracking with a deterministic collision model are combined with discrete ordinate methods for the radiation solver. Laser based techniques and flow probes provide particle concentration and velocity, gas temperature and radiation transmission statistics, as well as their correlations. The necessity of tailored post-processing for a one-to-one comparison of results is evidenced. |
Tuesday, November 20, 2018 3:13PM - 3:26PM |
Q37.00012: Abstract Withdrawn |
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