Beat Lüthi

Lagrangian measurement of vorticity dynamics in turbulent flow

The full set of velocity derivatives,

A Lagrangian investigation of the small-scale features of turbulent entrainment through particle tracking and direct numerical simulation

\partial u_{i}/\partial x_{j}

Velocity and temperature derivatives in high-Reynolds-number turbulent flows in the atmospheric surface layer. Part 1. Facilities, methods and some general results

, is measured experimentally in a Lagrangian way in quasi-homogeneous isotropic turbulence. This is achieved by applying the three-dimensional particle tracking velocimetry (3D-PTV) technique to an electromagnetically forced flow with

On the evolution of material lines and vorticity in homogeneous turbulence

\hbox{\it Re}_{\lambda}\,{\thickapprox}\,50

Turbulence in dilute polymer solutions

. Checks based on precise kinematic relations show that the technique presented measures the velocity derivatives with good accuracy. In a study on vorticity, characteristic properties of turbulent flows known from direct numerical simulations are reproduced. These are the positive skewness of the intermediate eigenvalue of the rate of strain tensor,

Investigations on the local entrainment velocity in a turbulent jet

s_{ij}

Expanding the Q – R space to three dimensions

,

Velocity and temperature derivatives in high-Reynolds-number turbulent flows in the atmospheric surface layer. Part 2. Accelerations and related matters

\langle \Lambda_{2}\rangle \,{>}\,0

Velocity and temperature derivatives in high- Reynolds-number turbulent flows in the atmospheric surface layer. Part 3. Temperature and joint statistics of temperature and velocity derivatives

, the predominance of vortex stretching over vortex compression,

Mapping mean and fluctuating velocities by Bayesian multipoint MR velocity encoding-validation against 3D particle tracking velocimetry

\langle \omega_{i}\omega_{j}s_{ij}\rangle \,{>}\,0