An experimental study of the velocity distribution and transition to turbulence in the aorta

Abstract

The development and evaluation of a hot-film probe, suitable for use within arteries and operated with a commercial constant-temperature anemometer and linearizcr, is described. The performance of the system in the recording of arterial velocity wave forms is described, and instantaneous and time-averaged velocity profiles constructed from measurements in the thoracic aorta of dogs are presented. The profiles were blunt, with boundary layers estimated to be less than 2 mm thick throughout the cycle, and significant skews were observed, the explanation for which appears to lie in the influence of local geometry on the flow. A preliminary study of flow disturbances in the aorta based on visual observation of instantaneous velocity wave forms and frequency spectrum analysis is reported. The occurrence of flow disturbances and turbulence is shown to be related to peak Reynolds number and the frequency parameter α. The possible roles of free-stream disturbances and boundary-layer transition in generating these disturbances are discussed.

Three-dimensional instabilities and transition of steady and pulsatile axisymmetric stenotic flows

“…Note that the images at t = 40T and t = 41T have almost exact reflection symmetry about the tube centre-plane, consequent on the period-doubling bifurcation of the instability mode. Reynolds number is contrary to the experimental observation of Nerem, Seed & Wood (1972) who studied the transition to turbulence in the aorta of a dog, in the absence of a stenosis. Significant differences between the two studies occur in the geometric and inflow conditions which could reasonably lead to the alternative trends in critical Reynolds number with reduced velocity.…”

Flow instability and wall shear stress variation in intracranial aneurysms

“…Stability of pulsatile flow has been studied experimentally and numerically (Nerem et al 1972;Einav & Sokolov 1993;Straatman et al 2002;Blackburn & Sherwin 2007). Experimental study of flow in a straight pipe by Einav & Sokolov (1993) showed that pulsatile flows become 'turbulent' during the deceleration phase of oscillation at Reynolds number around 2000.…”

“…Straatman et al (2002) performed a linear stability analysis for plane pulsatile Poiseuille flow showing that pulsation may trigger instabilities. Nerem et al (1972) measured velocity in the aorta of dogs and reported transition to turbulence at the end of systole.…”

Physique des fluides appliquée à la dynamique des valves cardiaques

“…Dans les conditions physiologiques "normales" la caractéristique des écoulements intracardiaques généralement rapportée est l'absence de turbulence complétement développée (Taylor & Wade, 1973) bien que les nombres de Reynolds instantanés puissent atteindre 10 4 . Des mesures de vitesse dans l'aorte ascendante humaine ou canine montrent que l'écoulement est plutôt laminaire ou faiblement instable (Nerem & al., 1972). De même les observations effectuées in vivo (Hwang et al, 1977) ou sur modèles hydrodynamiques utilisant des valves naturelles ou artificielles montrent que pendant la phase initiale d'accélération (remplissage rapide du ventricule gauche ou phase initiale de l'éjection systolique) les champs de vitesse présentent un caractère d'écoulement à potentiel.…”