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 A3: Particle-Laden Flows: Compressibility, Heat and Mass Transfer Effects |
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Chair: Ali Mani, Stanford University Room: 102 |
Sunday, November 22, 2015 8:00AM - 8:13AM |
A3.00001: Particle size distribution effects in an irradiated turbulent gas-particle mixture Mona Rahmani, Gianluca Geraci, Gianluca Iaccarino, Ali Mani The effects of particle size distribution on thermodynamic and hydrodynamic behavior of solid particle solar receivers, that involve a turbulent mixture of gas and particles in a radiation environment, are investigated, using DNS with point particles. The turbulent flow is seeded with monodisperse and polydisperse particles, where the mass loading and total frontal area of particles are matched between the two systems. The results show that the variability of the Stokes number for polydisperse particles can significantly influence the particle clustering, and consequently the thermal performance of the system. In all cases studied, the preferential concentration is less pronounced for polydisperse as opposed to monodisperse particles. This reduced preferential concentration results in less heating of the particles, but more efficient energy release to the gas phase. Due to their different clustering patterns, polydisperse particles influence the Taylor scale of the flow in the turbulent gas phase. Polydispersity also implies variable thermodynamic and hydrodynamic properties of the particles. Our results show that the thermal behavior of the system with polydisperse particles is set by the integral measures for particle and gas momentum and thermal relaxation times. [Preview Abstract] |
Sunday, November 22, 2015 8:13AM - 8:26AM |
A3.00002: Motions of particles falling under gravity in a weakly turbulent Rayleigh-BĂ©nard convection Sangro Park, Changhoon Lee Motions of particles falling under gravity in a weakly turbulent convective flow within two parallel walls is studied numerically. Despite the importance of particle-laden convective flows, the vast majority of studies on Rayleigh-B\'enard convection in the last decade have focused on single-phase fluids. Therefore detailed analysis on the behaviors of particles in Rayleigh-B\'enard convection is required for fundamental understanding and practical purposes, i.e. prediction of precipitation, design of industrial cooling systems. In this study we use a direct numerical simulation using a pseudo-spectral method in a horizontally periodic channel. The particle motion is tracked by using four point-Hermite and fifth order-Lagrangian interpolation scheme. The flow condition is Rayleigh number 10$^6$, Prandtl number 0.7 with a large aspect ratio 6. Particles are influenced by drag force by fluid and gravity for the range of Stokes number 0.01 - 10 and Froude number 0.45. Collisions of particles or force on fluid by particle are not considered. We found that weak particle clustering near the bottom wall is observed at large Stokes number, a similar behavior of particle alignment along gravitational direction in isotropic turbulence, whereas small Stokes number particles quickly follow the motion of thermal structures. The mechanism is discussed using probability density functions of particle locations and average distances between closest particles, etc. [Preview Abstract] |
Sunday, November 22, 2015 8:26AM - 8:39AM |
A3.00003: Mass transfer in a flow past a non-porous catalyst sphere Bo Sun, Sudheer Tenneti, Shankar Subramaniam Mass transfer in a flow past a particle with a surface chemical reaction occurs in applications involving catalytic reaction. This type of the mass transfer problem has been analyzed by solving the convection-diffusion equation for Stokes flow (Acrivos et al. 1962) or flow at low Reynolds number (Taylor 1963, Gupalo et al. 1972). The objective of this study is to extend our understanding of this mass transfer problem to higher Reynolds number (up to 100) and assemblies of several particles by using particle-resolved direct numerical simulation (PR-DNS) of gas-solid flow. A uniform flow past a non-porous spherical particle with a first-order surface reaction is simulated. The non-dimensional reaction rate constant is the important parameter in the single particle case. The PR-DNS results at low Reynolds number for a single particle are first compared with 2D analytical solutions for concentration fields and the Sherwood number. Finally, the dependence of the concentration field on the non-dimensional reaction rate constant, and comparison of PR-DNS results with other Sherwood number correlations that use the Reynolds analogy to adapt Nusselt number correlations (which do not explicitly account for surface reactions) are explored at high Reynolds number. [Preview Abstract] |
Sunday, November 22, 2015 8:39AM - 8:52AM |
A3.00004: On the effect of the particle size distribution tails in irradiated turbulent gas-particle mixture Gianluca Geraci, Mona Rahmani, Ali Mani, Gianluca Iaccarino Previous investigations of irradiated particle-laden turbulent flows have shown that the heat transfer is sensitive to the particle size distribution when compared to its thermodynamical equivalent feed with homogeneous (monodisperse) particles. In this work we focus on the shape of the particles size distribution and, in particular, we show how the presence of long tails, at the same nominal mass loading, affects the heat transfer between the particles and gas. We use DNS of turbulence with point particles to show that a particle size distribution is able to mitigate the particle clustering and thus increases the efficiency of the energy transfer to the fluid. The addition of a right tail to the same particle size distribution, while redistributing the mass loading towards large particles, lowers the efficiency of the heat transfer to the gas. Furthermore, we show that the addition of a left tail has the opposite effect. The small particles increase the heat transfer, hence the average temperature of the gas at the outlet section. The simultaneous presence of both tails has the same impact on the behavior of the system as the inclusion of the right tail only, indicating the dominance of the large particles. [Preview Abstract] |
Sunday, November 22, 2015 8:52AM - 9:05AM |
A3.00005: Numerical Simulation of Shock Interaction with Deformable Particles Using a Constrained Interface Reinitialization Scheme Thomas L. Jackson, Prashanth Sridharan, Ju Zhang, S. Balachandar In this work we present axisymmetric numerical simulations of shock propagating in nitromethane over an aluminum particle for post-shock pressures up to 10 GPa. The numerical method is a finite-volume based solver on a Cartesian grid, which allows for multi-material interfaces and shocks. To preserve particle mass and volume, a novel constraint reinitialization scheme is introduced. We compute the unsteady drag coefficient as a function of post-shock pressure, and show that when normalized by post-shock conditions, the maximum drag coefficient decreases with increasing post-shock pressure. Using this information, we also present a simplified point-particle force model that can be used for mesoscale simulations. [Preview Abstract] |
Sunday, November 22, 2015 9:05AM - 9:18AM |
A3.00006: Heat Transfer and Drag of a Sphere: Variable Density and Buoyancy Effects Swetava Ganguli, Sanjiva Lele How do forces acting on a particle change in the presence of significant heat transfer from the particle, a variable density fluid or gravity? We define unit problems isolating subsets of these phenomena and solve them via particle resolved simulations. Our investigations are agnostic to the Boussinesq regime and encompass both, the short time (acoustic) behavior and the subsequent nearly-incompressible flow field that is established. Defining $\lambda $ as the ratio of the initial particle-fluid temperature difference to the far-field fluid temperature, we observe that the particle size affects the acoustic response whereas $\lambda $ and Re affects the low-Mach response. The heating of the fluid near the particle affects the drag significantly which is studied in a parameter space where Re, $\lambda $ and the Grashof number are varied. In the isothermal case, the drag computed numerically matches the drag correlation of Clift-Grace-Weber. For heated particles, using the density of the fluid at the particle surface in the correlation under-estimates the drag (e.g. by 30{\%} when $\lambda =$1), using the dynamic viscosity of the fluid at the particle surface over-estimates the drag (e.g. by 17 {\%} when $\lambda =$1) and using both still over-estimates the drag (e.g. by 13{\%} when $\lambda =$1). The deviations increase as $\lambda $ increases. [Preview Abstract] |
Sunday, November 22, 2015 9:18AM - 9:31AM |
A3.00007: Convergence of Beer's Law for Radiation Transmission in Particle-Laden Turbulent Flows Ari Frankel, Rick Rauenzahn, Gianluca Iaccarino, Ali Mani Discrete random particulate media have been shown to produce significant deviations from Beer's law for radiation transmission. Though particle-resolved ray tracing models can exactly resolve the transmission, the computational expense of such approaches can be prohibitive in settings involving many particles where the radiative transfer equation must be solved at every time step. In this work we investigate the validity of projecting Lagrangian particles onto an Eulerian concentration field and using Beer's law on a local basis. We take particle distributions produced from clustering in turbulent flows and perform both particle-resolved Monte Carlo ray tracing and Beer's law computations. We show that the error in the calculated transmission decreases as the grid is refined, but that the homogenization error increases rapidly as the grid size approaches the particle diameter. [Preview Abstract] |
Sunday, November 22, 2015 9:31AM - 9:44AM |
A3.00008: Investigation of unsteadiness in Shock-particle cloud interaction: Fully resolved two-dimensional simulation and one-dimensional modeling Zahra Hosseinzadeh-Nik, Jonathan D. Regele Dense compressible particle-laden flow, which has a complex nature, exists in various engineering applications. Shock waves impacting a particle cloud is a canonical problem to investigate this type of flow. It has been demonstrated that large flow unsteadiness is generated inside the particle cloud from the flow induced by the shock passage. It is desirable to develop models for the Reynolds stress to capture the energy contained in vortical structures so that volume-averaged models with point particles can be simulated accurately. However, the previous work used Euler equations, which makes the prediction of vorticity generation and propagation innacurate. In this work, a fully resolved two dimensional (2D) simulation using the compressible Navier-Stokes equations with a volume penalization method to model the particles has been performed with the parallel adaptive wavelet-collocation method. The results still show large unsteadiness inside and downstream of the particle cloud. A 1D model is created for the unclosed terms based upon these 2D results. The 1D model uses a two-phase simple low dissipation AUSM scheme (TSLAU) developed by [Hosseinzadeh-Nik {\it et.al}, 53rd AIAA Aerospace Sciences Meeting (2015)] coupled with the compressible two phase kinetic energy equation. [Preview Abstract] |
Sunday, November 22, 2015 9:44AM - 9:57AM |
A3.00009: Transient Simulation of Accumulating Particle Deposition in Pipe Flow James Hewett, Mathieu Sellier Colloidal particles that deposit in pipe systems can lead to fouling which is an expensive problem in both the geothermal and oil \& gas industries. We investigate the gradual accumulation of deposited colloids in pipe flow using numerical simulations. An Euler-Lagrangian approach is employed for modelling the fluid and particle phases. Particle transport to the pipe wall is modelled with Brownian motion and turbulent diffusion. A two-way coupling exists between the fouled material and the pipe flow; the local mass flux of depositing particles is affected by the surrounding fluid in the near-wall region. This coupling is modelled by changing the cells from fluid to solid as the deposited particles exceed each local cell volume. A similar method has been used to model fouling in engine exhaust systems (Paz et al., \textit{Heat Transfer Eng.}, \textbf{34}(8-9):674-682, 2013). We compare our deposition velocities and deposition profiles with an experiment on silica scaling in turbulent pipe flow (Kokhanenko et al., \textit{19th AFMC}, 2014). [Preview Abstract] |
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