Final Report Summary - TRITOS (TRansItions and Turbulence Of complex Suspensions) The aim of this project was to forge a physical understanding of the turbulent flow of semi-dilute/dense non-colloidal suspensions, for different particle features and suspending fluids. It is estimated that 10% of the world energy consumption is due to the transport and handling of granular materials of which particle suspensions are an important part. A deep understanding of the mechanisms underlying the flow of particle suspensions and the turbulence characteristics is crucial for many important practical applications involving engineered complex fluids, such as pastes and paper pulp. Complex fluids are multiscale by nature where the physics at the microscale affects the macroscopic behaviour of the flow and vice versa giving rise to surprising and spectacular phenomena as well as making this one of the most important practical problem still to solve. Investigating the mechanisms by which the system microstructure determines the macroscopic flow properties and vice versa will also lead to new ways to model and control it. Future generations of engineering CFD tools will have to contain models for complex suspensions. The work is based on highly accurate simulations of multiphase flow systems and state-of-the-art experiments. During the project we have developed tools for the accurate numerical simulations of turbulent flows of simple and complex fluids laden with rigid and deformable particles of different shapes, as well as elastic filament and droplets/bubbles. Analysis of the numerical simulations and of the corresponding laboratory experiments have revealed how turbulence is modulated by the presence of a suspended phase. Particle of different shapes have different dynamics, in particular rotation rates which has a huge impact on the global transport properties. In addition, we show how the presence of the particles has a more significant impact on the heat transfer and mixing inside the suspension than on the total drag, which changes by less than 10% when the main mechanism for momentum transfer changes from fluid turbulent fluctuations to particle-induced stresses. Our results also show how any future model of the flow of particle suspensions should consider particle migration and preferential accumulation.
