A shearing zonal flow of viscous fluid near a boundary perturbation can generate vortices that either remain attached near the boundary or detach to be abruptly carried downstream. At low speed a stationary attached vortex develops downstream from the perturbation. At higher speeds an array of traveling vortices forms, with successive rolls rotating in opposite directions. This report presents a quantitative explanation of vortex generation. We consider a setup that leads to a straightforwardly analyzable, Schrödinger-type equation. In the case of bloodflow through arteries the aforementioned traveling vortices are detectable as oscillations in the 1-100 Hz range. The detection of such oscillations is simple and is used to diagnose arterial stenosis.