Heat transfer from an array of resolved particles in turbulent flow

The physalis method for resolved numerical simulation of particulate flows, recently extended to include particles-fluid heat transfer, is applied to the turbulent flow past a planar particle array perpendicular to the incoming mean flow. The array consists of nine equal spheres. Periodicity boundary conditions are imposed on the boundaries of the computational domain parallel to the mean flow. The Reynolds number based on the particle diameter and mean incident flow is 120, the Taylor-scale Reynolds number is close to 30, and the ratio of particle radius to the Kolmogorov length is about 10. A detailed characterization of the flow and heat transfer is given including probability distribution functions of temperature and streamwise velocity, contour maps of the temperature fluctuations, diagonal Reynolds stresses, turbulent heat flux, and the various contributions to the energy budget. Turbulence moderately increases the heat transfer and considerably shortens the thermal wake of the particles. Temperature and streamwise velocity develop very differently downstream of the spheres in spite of the fact that the Prandtl number equals 1, because of the blockage by the spheres, which has no counterpart for the temperature

Rotational dynamics of a particle in a turbulent stream

The paper presents results for the resolved numerical simulation of a turbulent flow past a homogeneous sphere and a spherical shell of equal mass and radius (and, therefore, with a larger moment of inertia) free to rotate around a fixed center. This situation approximates the behavior of a particle whose relative motion with respect to the fluid is driven by external forces, such as a density difference in a gravitational field. Holding the center fixed makes it possible to have precise information on the turbulent flow incident on the particle by repeating the same simulations without the particle. Two particle Reynolds numbers based on the mean velocity, Re p = 80 and 150, are investigated; the incident turbulence has Re ? = 36 and 31, respectively. The particle diameter is an order of magnitude larger than the Kolmogorov length scale and close to the integral length scale. The turbulent eddies that interact most strongly with the particle are characterized. Their size is found to increase with Re p due to the interplay of the convection timescale, the particle timescale, and the eddy timescale, but it remains of the order of the particle diameter. The sign of the hydrodynamic torque is likely to persist much less than the convection time, although longer durations are also found, revealing the effect of occasional interactions with larger eddies. The autocorrelation of the torque changes sign at shorter and shorter fractions of the convection time as the Reynolds number increases. Significant cross-stream forces are found. An analysis of their magnitude shows that they are mostly due to induced vortex shedding combined with a weaker Magnus-like mechanism

Fully-resolved simulations of heat transfer in particle-laden flows

Solid particles suspended in a fluid flow are encountered in many industrial applications, environmental processes and natural systems, such as fluidized beds, cloud formation, dust and pollutants dispersion, industrial mixers, oceanic plankton and many others. In the present dissertation we carry out fully resolved numerical simulations of several problems in this general area both with and without particles-fluid heat transfer. An important aspect of the work is that the finite size of the particles is properly accounted for and that the fluid dynamic forces acting on them are based on an accurate solution of the fluid equations rather than parameterized. The general approach used in this study is based on the PHYSALIS method. This method uses local analytic solutions as “bridges" between the particle surfaces and a fixed underlying Cartesian grid. For the isothermal case, we study the rotational dynamics of a particle free to rotate around a fixed center in a turbulent flow. Fixing the particle center and carrying out parallel simulations of the flow without the particle enables us to fully characterize the flow incident on the particle. We determine the scales of eddies interacting most with the particle and explore the effect of vortex shedding on the rotational dynamics. The Magnus mechanism is not found to play a significant role. To account for particles-fluid heat transfer phenomena, we have extended PHYSALIS to deal with the energy equation. This new direct numerical simulation method for non-isothermal systems is described in detail and extensively validated against experimental studies and analytical solutions. The method is implemented numerically on a GPU-centric code, which is compatible with BLUEBOTTLE – a highly efficient GPU-centric computational fluid dynamics framework. An example of particles transported by a Rayleigh-Bénard convective flow is shown to demonstrate the potential applications of our method. A further application to the thermal wake of particles in turbulent flow is also given