Experimental investigation of exit dynamics of a circular cylinder out of water and silicone oil

TL;DR

This study experimentally investigates the exit dynamics of a horizontal cylinder from water and silicone oil, analyzing effects of initial depth, exit speed, and fluid properties on entrainment, wake, and drainage behaviors.

Contribution

It provides new insights into the influence of initial conditions and fluid properties on the entrainment and drainage dynamics during cylinder exit in different fluids.

Findings

Liquid entrainment thickness increases logarithmically with exit speed.

Drainage thickness decreases exponentially then follows inverse square root of time.

Force measurements confirm square root scaling of drainage thinning.

Abstract

Experimental investigations of the exit dynamics of a horizontal cylindrical object were performed in water and silicone oil (50 cSt). The fully immersed cylinder was initially at rest in a still fluid tank before being pushed (or pulled according to the measurement procedure) upwards at a constant velocity. Firstly, we demonstrate that these conditions are better satisfied for a large aspect ratio cylinder equipped with vertical side plates. Secondly, the influence of the initial depth on the liquid entrained and the wake generated by the cylinder is discussed. The deformation of the bath is found to be independent of the starting depth when the starting depth is larger than 6 times the cylinder diameter. In the present case, this criterion reflects also the finite acceleration of the cylinder to reach the determined constant exit velocity. Measurements in a range of exit speeds between 0.1 and 1 m/s indicate that the thickness of the liquid above the cylinder, when the cylinder starts crossing the interface, increases with the speed according to a logarithmic law of the Froude number. During the subsequent drainage, the evolution of the coated liquid thickness is found to first decrease exponentially with time just after the crossing of the interface. At later times, a change of regime occurs and the drainage follows the inverse of the square root of time irrespective of the crossing speed. Finally, the force necessary to maintain a constant exit speed during the motion of the cylinder inside and outside the bath is analyzed. This global measurement of the entrained liquid confirms the square root scaling of the thinning with time during the drainage process.