Flow behaviour of blood cells and rigid spheres in an annular vortex

Abstract

Results have been presented on the size and shape of an annular vortex seen in the common median plane of a sudden concentric expansion when suspensions of red cells, platelets and rigid spheres are subjected to steady and pulsatile flow. In steady flow, the location of the vortex centre, the reattachment point and the velocity distributions were in good agreement with theory. In pulsatile flow, the vortex appeared to oscillate in phase with the upstream fluid velocity U (r, t ), symmetrically about a location corresponding to its position in the absence of the oscillatory flow component. The most interesting and novel observations, however, and those which prompted this investigation, were concerned with the migration of red cells, platelets and rigid spheres across the fluid streamlines of the annular vortex. Such radial migration, dependent in magnitude and direction on Reynolds number and particle size, may have interesting implications for the dynamics of blood flow in arteries. Before dealing with this question and the possible mechanism underlying particle migration, the observations on cell orientations in the vortex are first discussed.