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Numerical simulations of rigid particles and droplets in turbulent shear flows Brandt, Luca


Novel efficient numerical algorithms and large-scale super computers are enabling interface-resolved simulations of turbulent multiphase flows, giving access to details that improve our fundamental understanding and provide input for modelling efforts. In particular, we will first consider heat and mass transfer in particulate suspensions and perform direct numerical simulations to study the heat transfer within a suspension of neutrally buoyant, finite-size spherical particles in laminar and turbulent pipe flows, using the immersed boundary method (IBM) to account for the solid fluid interactions and a volume of fluid (VoF) method to resolve the temperature equation both inside and outside the particles. We examine particle volume fractions up to 40% for different pipe to particle diameter ratios. We report a considerable heat transfer enhancement (up to 330%) in the laminar regime by adding spherical particles, where larger particles are found to have a greater impact on the heat transfer enhancement than on the wall-drag increase. In the turbulent regime, however, only a transient increase in the heat transfer is observed and the heat flux decreases below the values in single-phase flows as high volume fractions of particles laminarize the core region of the pipe. A heat transfer enhancement, measured with respect to the single phase flow, is only achieved at volume fractions as low as 5% in a turbulent flow. Finally, we will consider emulsions in laminar and shear flows and examine the role of surfactants and short-range interaction forces on the rheology. As concerns the turbulent regime, we study homogeneous shear turbulence and report attenuation in the presence of a dispersed second phase. WE show how droplets break up and coalesce to reach a steady state number, with large size following the Hinze prediction.

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