Laboratoire Matière et Systèmes Complexes

PhD defence of Alexis Duchesne. Directors: Laurent Limat and Luc Lebon.

Mercredi 10 Décembre 2014 à 14h00

Lieu : Salle 265E bâtiment Halle aux Farines.

La soutenance sera suivie d’un pot au 6e étage du Bâtiment Condorcet.

Three problems about the circular hydraulic jump.

Abstract

A liquid jet colliding with a horizontal surface generates a flow divided in two regions. Close to the impact point, the flow is fast and the fluid layer is thin while further downstream the layer is thick and the flow is slow. The boundary between these inner and outer flows is characterized by a sharp liquid wall, known as the circular hydraulic jump. Here, we study how the properties of the jump depend on flow conditions, geometry and wettability. We provide also a description of the motion of a non-coalescent drop in the inner fast flow region.

First, we investigate jump radius selection. We show that the Froude number (ratio between flow speed and gravity-wave velocity) measured at the jump exit is independent of physical parameters and weakly dependent on geometrical parameters. Combining these results with a lubrication description of the outer flow we obtain a simple law predicting the jump radius in excellent agreement with our measurements.

Second, we study a jet
 colliding perpendicularly with an inclined surface for three different wetting conditions: total, partial wetting and non-wetting. The flow
 features a hydraulic jump near the impact and a
 curved wetting front at larger distance whose evolution we explore and model depending on slope and flow rate.

Finally, we explore the dynamics of a non-coalescing drop inside a circular jump. The drop is moving along the jump following a regular orbital motion, or an irregular motion involving inversions. Modeling the drop as a rigid sphere exchanging friction with liquid across a thin film of air, we rationalize both the orbital motion and the internal rotation of the drop.