Anne Cros

Date:  November 17th, 2022.  At 5:00 pm (Mexico time).

Title : Sky dancer, a complex system

Abstract : 

Sky dancers are those large, fabrics-made tubes which fluctuate above an air blower. In this work, we reproduce in our laboratory such a system in a reduced size. For easier measurements, we put this system upside down in such a way that air flows from the fixed, upper tube end to its free bottom extreme. We observe that in this configuration, the tube exhibits strange, stable, static zig-zag states which are constituted by three roughly straight segments. We experimentally characterize each shape by the lengths and angles of these three segments and we use a model of three articulated straight rigid tubes conveying airflow to reproduce the zig-zag states. In the second part, we characterize the intermittent regime which appears in our system. The chaotic or static states are identified through the pressure signal, which exhibits two kinds of behavior. The turbulent phase duration scale exponentially while the laminar phases display algebraic statistics. The coexistence of these two distinct laws for the same value of the control parameter value can be modeled on the basis of two competing stochastic processes with different time scales. The first one refers in our case to the local flow velocity and the other one is a critical velocity related to the tube geometrical variable shape which is quenched during the laminar phases but rapidly varying during the turbulent phases.

Youtube link : https://youtu.be/v7tEh6NyCAc