# Fluid Mechanics and Acoustics Laboratory - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique
Lyon
France

## Wouter Bos

Research Team: Turbulence & Instabilities

tel: 04.72.18.62.04
email

Research in the spotlight:

### Power fluctuations in turbulence [with Rémi Zamansky (IMFT)]

How universal are the power-fluctuations measured in the electricity output of a windmill? Indeed, the power fluctuation experienced by a windmill blade are determined by the power absorbed by the incoming, turbulent airflow. The universal character of turbulent power fluctuations is, in general, of major importance in the modeling and understanding of fluid flows in industry, geophysics and astrophysics. However, the manner in which the turbulence is generated can be radically different in different types of flows, so that it seems improbable that universality is observed among different types of flow. Nevertheless, we show that different turbulence generating mechanisms can lead to similar statistics of the energy input since the input is not only determined by the forcing mechanism, but also by the turbulent flow itself.

### Football players and turbulent trajectories (with B. Kadoch and K. Schneider)

(...) Indeed, even though a football match does not seem to be ergodic, and some may argue that the trajectories of football players are not completely random, the long-time PDF of the directional change converged to a shape close to the one for fluid particles (...)

Recent experiments and simulations have shown that unsteady turbulent flows display a universal behavior at short and intermediate times, different from classical scaling relations. The origin of these observations is explained and the exact form of the observed universal scaling is derived. The derived scaling for the normalized dissipation rate $C_\epsilon$ as a function of the Reynolds number $R_\lambda$ is,
$$C_\epsilon\sim R_\lambda^{-15/14},$$