It has long been known that a cylindrical obstacle placed in a moving fluid generates a vortex trail. The frequency of vortex detachment is related to the non-dimensional Strouhal number, S. For Newtonian fluids
at Reynolds number
and increases to a constant ≃ 0.20 at
. The equivalent relationships for blood were determined and found to be considerably different. Strouhal number for blood showed a correlation with the Reynolds number only when S’s obtained with a given cylinder were considered. They were 3 times greater than for Newtonian fluids at threshold R (i.e. R at which vortices begin to detach), and they decreased with increasing R.
