Séminaire au LOG par Eric CLIMENT - Institut de Mécanique des Fluides de Toulouse intitulé :
Dynamics of motile plankton in turbulent environment (from single cells to chain formation)
Date : 11 octobre 2016
Lieu : LOG salle de conférences à la MREN Wimereux
Daily, phytoplankton needs to migrate vertically from and towards the ocean surface to find nutrients such as dissolved oxygen. To travel through the water column they need to fight against gravity (by swimming) and fluid turbulence which can make their journey longer. We carried out direct numerical simulations and physical analysis of the coupled system of homogeneous isotropic turbulence and trajectories of gyrotactic plantkon cells through Lagrangian tracking.
It is often observed that cells migrate across the water column as chains. The first benefit to form chains is that micro-organisms sum up their thrust while reducing their drag. Therefore, upwards swimming is faster for chains in a quiescent fluid with steady vertical orientation. However, as chain length increases their tendency to periodically tumble in turbulent structures increases which reduces orientation stability and limits their capacity to swim upwards. The purpose of our study is to elaborate on this apparent contradiction.