Steady and unsteady flow within an axisymmetric tube dilatation

Stamatopoulos, Ch; Papaharilaou, Y; Mathioulakis, DS; Katsamouris, A

dc.contributor.author	Stamatopoulos, Ch	en
dc.contributor.author	Papaharilaou, Y	en
dc.contributor.author	Mathioulakis, DS	en
dc.contributor.author	Katsamouris, A	en
dc.date.accessioned	2014-03-01T01:34:41Z
dc.date.available	2014-03-01T01:34:41Z
dc.date.issued	2010	en
dc.identifier.issn	0894-1777	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/20792
dc.subject	Flow separation-reattachment	en
dc.subject	Tube dilatation	en
dc.subject	Vortex	en
dc.subject	Wall shear	en
dc.subject.classification	Thermodynamics	en
dc.subject.classification	Engineering, Mechanical	en
dc.subject.classification	Physics, Fluids & Plasmas	en
dc.subject.other	2-D PIV	en
dc.subject.other	Absolute values	en
dc.subject.other	Axial velocity	en
dc.subject.other	Axisymmetric	en
dc.subject.other	Cavity regions	en
dc.subject.other	Flow reattachment	en
dc.subject.other	Flow topology	en
dc.subject.other	Fluid particles	en
dc.subject.other	Local maximum	en
dc.subject.other	Longitudinal axis	en
dc.subject.other	Massless particles	en
dc.subject.other	Near fields	en
dc.subject.other	Numerical code	en
dc.subject.other	Numerical predictions	en
dc.subject.other	Pressure peaks	en
dc.subject.other	Pressure variations	en
dc.subject.other	Recirculation zones	en
dc.subject.other	Separated flows	en
dc.subject.other	Stagnation points	en
dc.subject.other	Stress values	en
dc.subject.other	Time progress	en
dc.subject.other	Time-dependent flow	en
dc.subject.other	Tube dilatation	en
dc.subject.other	Velocity profiles	en
dc.subject.other	Vortex	en
dc.subject.other	Vortex rings	en
dc.subject.other	Wall pressure	en
dc.subject.other	Wall shear	en
dc.subject.other	Wall shear stress	en
dc.subject.other	Womersley numbers	en
dc.subject.other	Flow separation	en
dc.subject.other	Shear stress	en
dc.subject.other	Strength of materials	en
dc.subject.other	Tubes (components)	en
dc.title	Steady and unsteady flow within an axisymmetric tube dilatation	en
heal.type	journalArticle	en
heal.identifier.primary	10.1016/j.expthermflusci.2010.02.008	en
heal.identifier.secondary	http://dx.doi.org/10.1016/j.expthermflusci.2010.02.008	en
heal.language	English	en
heal.publicationDate	2010	en
heal.abstract	The flow field in an axisymmetric tube dilatation is studied employing a 2D PIV system and the commercial numerical code FLUENT. Experiment and numerical predictions are in good agreement providing similar trends and the same flow topology. For the steady case and for Re varying in the range 100-700, the recirculation zone length increases with Re, the flow reattachment line being displaced towards the exit of the model. Upstream of this line and a small distance from it, negative velocity maximizes close to the wall as well as the wall shear stress (in absolute value). Downstream of this region, the wall pressure peaks and wall shear takes a local maximum at the model exit. In the rest part of the cavity both wall shear and pressure do not practically vary due to separated flow. The axial velocity on the longitudinal axis of the model does not change streamwise for higher Re (Re = 690), resembling the near field of a jet, entraining fluid from the cavity region. In the unsteady case the flow rate is sinusoidal, the Womersley number is 3.3 and peak Re = 272. During early acceleration, a vortex ring is formed at the proximal part of the cavity and two stagnation points appear on the longitudinal axis of the model approaching each other as time progresses, eventually disappearing when the majority of the fluid particles changes direction. The velocity profile at the exit is most of the cycle blunt compared to the parabolic type profile at the model entrance. In contrast to the steady case, the pressure variation does not exhibit a local peak within the cavity rather varying in a smooth way. Conversely, wall shear stress shows high peaks at the distal end of the dilatation being proportional to the time dependent flow rate. The reattachment line travels along the wall, as well as the local pressure peak which is always located downstream of it. Massless particles released at various locations and time instants within a cycle are not trapped in the recirculation zone, being exposed to varying shear stress values. (C) 2010 Elsevier Inc. All rights reserved.	en
heal.publisher	ELSEVIER SCIENCE INC	en
heal.journalName	Experimental Thermal and Fluid Science	en
dc.identifier.doi	10.1016/j.expthermflusci.2010.02.008	en
dc.identifier.isi	ISI:000278510700011	en
dc.identifier.volume	34	en
dc.identifier.issue	7	en
dc.identifier.spage	915	en
dc.identifier.epage	927	en