Transverse and lateral confinement effects on the oscillations of a free cylinder in a viscous flow

Abstract

The different types of instabilities of free cylinders (diameter $D$, length $L$) have been studied in a viscous flow (velocity $U$) between parallel vertical walls of horizontal width $W$ at a distance $H$: the influence of the confinement parameters $D/H$ and $L/W$ has been investigated. As $D/H$ increases, there is a transition from stable flow to oscillations transverse to the walls and then to a fluttering motion with oscillations of the angle of the axis with respect to the horizontal. The two types of oscillations may be superimposed in the transition domain. The frequency $f$ of the transverse oscillations is independent of the lateral confinement $L/W$ in the range: 0.055 \le L/W \le 0.94$foragivencylindervelocity$V_{cx}$andincreasesonlyweaklywith$V_{cx}$.Theseresultsareaccountedforbyassuminga2Dlocalflowoverthecylinderwithacharacteristicvelocityindependentof$L/W$foragiven$V_{cx}$value.Theexperimentalvaluesof$f$arealsoindependentofthetransverseconfinement$D/H$.Thefrequency$f_f$oftheflutteringmotionissignificantlylowerthan$f$:$f_f$isalsonearlyindependentofthecylinderdiameterandoftheflowvelocitybutdecreasessignificantlyas$L/W$ increases. The fluttering instability is then rather a 3D phenomenon involving the full length of the cylinder and the clearance between its ends and the side walls.

References in corpus (2)

• Influence of flow confinement on the drag force on a static cylinder
• Oscillations and translation of a free cylinder in a confined flow