High-speed tracking of zooplankton in flow

The Holzner group has pioneered the application of three-dimensional high-speed video tracking to planktonic copepods. Copepods are among the most abundant metazoans in the ocean, and constitute a vital trophic link within marine food webs. They live in flowing environments and are routinely exposed to turbulence. However, their ability to adapt to turbulence remained unclear. The Holzner group developed an advanced particle tracking approach to simultaneously measure the trajectories of zooplankton and the flow field around them, which allowed decoupling of the relative velocity of swimming zooplankton from that of the underlying flow. This high-speed tracking approach provides the basis for investigating encounter rates with conspecifics and microplastics.

Current contributor: Dr. Ron Shnapp

Former contributors: Dr. François-Gaël Michalec, Dr. Itzhak Fouxon

Biomedical flows

The dynamics of blood flow also known as haemodynamics plays a crucial role in the understanding of the evolution of cardiovascular disease and in the development of optimal medical devices. In fact, the presence in the flow of specific helical and vortical patterns, of shear-induced turbulence, of oscillating shear stress at the wall and of stagnation zones is closely related to pathological states or can be caused by the introduction of non-optimal cardiovascular implants. We thus study the impact on the flow of aortic stenosis, aneurysm, arrhythmogenic right ventricular dysplasia to help in the diagnosis and severity assessment of these pathologies. We also investigate the flow downstream of artificial heart valves and around the wires of stents with ferrofluid coating in order to improve the performance of such devices. Read More

Current contributors: Till Zeugin and Dr. Marius Mihai Neamtu Halic

Former contributor: Dr. Utku Gulan, Dr. Pascal Corso and Dr. Laura Maria Stancanelli

Stratified turbulence

Stratified turbulence occurs in nature when water is discharged into lakes or the ocean; it appears above the atmospheric boundary layer, where buoyancy forms plumes of cumulus clouds; and it is central in the design of heat exchangers, where cold fluid entering the top of the exchanger rapidly falls and mixes with warm fluid underneath. Coherent flow structures play a key role in these flows by controlling the overall rate of mass and momentum transport. However, progress in our understanding of the mechanics of these flow structures has been hampered by arbitrariness in the detection methods of these coherent flow structures and hence leading to contrasting classifications of the results or even misinterpretations of physical mechanisms. Read More

Current contributor: Stefano Brizzolara

Former contributor: Dr. Lukas Schmidt and Dr. Marius Mihai Neamtu Halic

Porous medium flow

Previous experimental research on porous medium flow and transport suffered from the difficulty of obtaining information on both fluid flow and structure at the pore-scale and in three dimensions. We developed a novel approach that combines three-dimensional particle velocimetry and X-ray microtomography to study Lagrangian velocities and acceleration, the development of biofilms and transport of colloids in porous media. Key findings include the relation between geometry and intermittent motion of particles in porous media, the influence of pore network geometry and wall shear stress on biofilm development and a model for the stochastic dynamics of flow particles in porous media.

Current contributor: Dr. Alon Nissan

Former contributors: Dr. Quirine Krol, Prof. Veronica Morales, Dr. Maxence Carrel

Snow particles dynamics

A deeper insight into the motion of snow particles in the atmosphere is of great importance to understand snow precipitations, snow distribution on the ground, and physical processes within the crystals. Snowflakes are single and aggregated ice crystals that form in clouds from water vapor at a wide range of physical conditions. Their intricate trajectories originate from a complex interaction with the surrounding air that may influence the spatial distribution and interaction between falling snow particles. We are developing a novel numerical model based on Large Eddy Simulations (LES) combined with the solution of the rigid body equation of motion of snow particles, validated with experiments based on 3D-printed snowflakes geometries. Read More

Current contributors: Giorgia Tagliavini and Till Zeugin

Former contributor: Dr. Quirine Krol