Wider research context

Particle-laden flows surround us, from micro to planetary scales. When the size of the particles is small compared to the smallest scale of the flow and the particle concentration is very low, one can use point-particle models to predict the hydrodynamic forces on the particles and ignore particle-particle interactions. However, these assumptions are often not fulfilled and our predictive capability is still poor. Solving all the scales of the problem has a huge computational cost, thus restricted to research and very simple configurations, typically a triply-periodic set-up.

Hypotheses and research questions

In this project we consider gravity as the driving force of the problem. We impose periodicity in the directions perpendicular to gravity, but not in the vertical direction. Vertical non-periodicity presents a series of challenges when considering gravity-driven flows and opens new possibilities as a novel configuration. Some of the open questions we plan to answer in this project: what is the average particle distribution along the vertical direction when it is not imposed? (please note that in a triply-periodic configuration the average particle distribution is imposed in all directions). Are results for triply-periodic configurations reproduced? Is there any kind of cluster stability by which clusters are compacted and sustained in time? We will also analyse questions regarding the flow fluctuations generated by the particles. Is turbulence generated only at the small scales (boundary layers and wakes)? or do clusters generate large scale motions that recover the classical picture of the energy cascade?

Methods

We plan to use particle-resolved direct numerical simulations. More specifically, we will run massively parallel simulations and develop post- processing techniques for the analysis of cluster dynamics. We will also work with low-order models, mainly incorporating non-homogeneity in Euler-Euler approaches.

Innovation

The main novelty in this project is the removal of the periodicity in the vertical direction. This might be overlooked as a simple and small modification, but it has large implications and brings many new ingredients to the problem. First, it represents a more realistic configuration to analyze the settling of particles compared to the previous works in which triply periodic cases were analysed. The distribution of particles along the vertical direction is now a result, therefore giving insight of the actual particle distribution in a real case. Important elements that before were not possible to observe, can now be analysed, namely the effect of the fresh fluid seen by the particles located at the settling front or the tendency of particles to stay together (compared to their initial condition) or separate.

Primary researchers involved

Manuel Moriche (PI), Manuel García-Villalba (head of PI's research group) and Markus Uhlmann (International collaborator).