BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Memento EPFL//
BEGIN:VEVENT
SUMMARY:Virtual MEchanics GAthering -MEGA- Seminar: Talk 1 - Scaling and m
 odelling of vortex rings behind cones\; Talk 2- Discrete shedding of secon
 dary vortices along a modified Kaden spiral
DTSTART:20210318T161500
DTEND:20210318T173000
DTSTAMP:20260510T183529Z
UID:c38955e184cc1dcb4dd5aadd39ef88df8250d7766ca205aadff8434b
CATEGORIES:Conferences - Seminars
DESCRIPTION:Guillaume de Guyon & Diego Francescangeli (UNFOLD\, EPFL)\nT
 alk 1: Scaling and modelling of vortex rings behind cones\, by Guillaume 
 de Guyon (UNFOLD\, EPFL)\n\nAbstract Ring vortices are efficient at trans
 porting fluid across long distances. They are observed in nature in variou
 s ways: they propel squids\, inject blood in the heart\, and entertain dol
 phins. These vortices are generally produced by ejecting a volume of fluid
  through a circular orifice and have been widely studied and characterised
 . After four convective times\, three events happen simultaneously: the vo
 rtex moves faster than the shear layer it originates from\, it separates f
 rom the shear layer\, and the circulation and non-dimensional energy of th
 e vortex converge. The simultaneity of these three events obfuscates the c
 ausality between them. To analyse the temporal evolution of the vortex ind
 ependently of the separation\, we analyse the development of vortices gene
 rated in the wake of cones. The vortex rings that form behind the cones ha
 ve a self-induced velocity that causes them to follow the cone. They conti
 nue to grow as the cone travels well beyond the limiting vortex formation 
 times observed for vortices generated by pistons. The non-dimensional circ
 ulation\, based on the vortex diameter\, and the non-dimensional energy of
  the vortex rings converge after three convective times. This result prove
 s that the convergence of non-dimensional quantities is not just a consequ
 ence of the separation. In addition\, the evolution of the vortex is model
 led with an axisymmetric discrete vortex method. The model predicts accura
 tely the evolution of the vortex.\n\nBio Guillaume de Guyon is a PhD stud
 ent in the Unsteady flow diagnostics Laboratory\, under the scientific sup
 ervision of Prof. K. Mulleners. He obtained his M.Sc. in Mechanics in the 
 Sorbonne university (Paris\, France) in 2016. During his studies\, he got 
 interested in theoretical fluid mechanics\, which brought him to his PhD d
 evoted to the study of vortex formation.\n\nTalk 2: Discrete shedding of s
 econdary vortices along a modified Kaden spiral\, Diego Francescangeli (U
 NFOLD\, EPFL)\n\nAbstract When an object is accelerated in a fluid\, a pr
 imary vortex is formed through the roll-up of a shear layer. This primary 
 vortex does not grow indefinitely and will reach a limiting size and stren
 gth. Additional vorticity beyond the critical limit will end up in a trail
 ing shear layer and accumulate into secondary vortices. The secondary vort
 ices are typically considerably smaller than the primary vortex. In this p
 aper\, we focus on the formation\, shedding\, and trajectory of secondary 
 vortices generated by a rotating rectangular plate in a quiescent fluid us
 ing time-resolved particle image velocimetry. The Reynolds number (Re) bas
 ed on the maximum rotational velocity of the plate and the distance betwee
 n the centre of rotation and the tip of the plate is varied from 840 - 111
 50. At low Re\, the shear layer is a continuous uninterrupted layer of vor
 ticity that rolls up into a single coherent primary vortex. At Re = 1955\,
  the shear layer becomes unstable and secondary vortices emerge and subseq
 uently move away from the tip of the plate. For Re = 4000\, secondary vort
 ices are discretely released from the plate tip and are not generated from
  the stretching of an unstable shear layer. First\, we demonstrate that th
 e roll-up of the shear layer\, the trajectory of the primary vortex\, and 
 the path of secondary vortices can be predicted by a modified Kaden spiral
  for the entire Re range considered. Second\, the timing of the secondary 
 vortex shedding is analysed using the swirling strength criterion. The sep
 aration time of each secondary vortex is identified as a local maximum in 
 the temporal evolution of the average swirling strength close to the plate
  tip. The time interval between the release of successive secondary vortic
 es is not constant during the rotation but increases the more vortices hav
 e been shed. The shedding time interval also increases with decreasing Rey
 nolds number. The increased time interval under both conditions is due to 
 a reduced circulation feeding rate.\n\nBio Diego Francescangeli is a PhD 
 student in the Unsteady flow diagnostics Laboratory\, UNFoLD under the sup
 ervision of Prof. K. Mulleners. He obtained his M.Sc. in Mechanical engine
 ering in the Marche polytechnic university (Ancona\, Italy) in 2017.  For
  his Master thesis\, he had an intership in Belgium at von Karman Institut
 e\, to study the cavitation. From this experience\, he developed a growing
  interest in fluid dynamics\, which leads him to start a PhD about vortex 
 dynamics.
LOCATION:https://epfl.zoom.us/s/84678428267 Passcode: 174387 https://epfl.
 zoom.us/s/84678428267
STATUS:CONFIRMED
END:VEVENT
END:VCALENDAR