Measuring flow reattachment lengths downstream of a stenosis using MRI

Flow reattachment lengths (l(r)) are measured downstream of an abrupt axisymmetric 75% stenosis, located inside a cylindrical channel, for steady flow using ultra-fast magnetic resonance imaging (MRI). The MRI results are compared with those from other similar (non-MRI) studies. The MRI data confirm the existence of three flow reattachment regimes (laminar, fully turbulent, and transition) related to the flow Reynolds number (Re) measured inside the stenosis. Based on the MRI experiments, the laminar regime occurs at a stenotic Reynolds number below 250 with a slope (l(r)/Re) of 0.086. The fully developed turbulence occurs at a stenotic Reynolds number above 3600 with a minimum observed reattachment length of 5 step heights. The transition regime (occurring between the laminar and fully turbulent regimes) is characterized by a reattachment length plateau and then a drop with Re^-1.1. (C) 2000 Wiley-Liss, Inc.