Seminar - The Pirouette Effect in Turbulent Flows: An Example of What Can Be Learned from Lagrangian Tetrads

The dynamics of the velocity gradient tensor, and in particular of vorticity, plays a crucial role for our understanding of turbulent flows. I will discuss recent numerical and experimental results concerning the "perceived velocity gradient tensor", constructed with the help of 4 points (a tetrad).

The evolution of the shape of the tetrad and of the perceived velocity gradient tensor sheds new light on the intriguing properties of alignment between vorticity and the strain eigenvectors observed in turbulent flows.