The interaction of a spanwise vortex with a boundary layer has been nu
merically simulated using a fractional-step method. The incompressible
Navier-Stokes equations are solved to accurately predict the strong v
iscous-inviscid interaction between a vortex either near or embedded w
ithin a boundary layer of comparable size. A strong vortex induces an
eruption and the production of a secondary vortex. The secondary vorte
x causes the primary vortex to rebound, a response observed in many pr
evious experiments and numerical simulations. However, weaker vortices
as well do not follow the inviscid trajectory despite the absence of
a secondary vortex. Rather than creating vorticity at the wall, a weak
er vortex mainly redistributes the vorticity of the boundary layer, pu
lling it away from the wall. The redistributed vorticity alters the pa
th of the vortex. In the laminar cases studied the decay of the vortex
is not significantly altered by the boundary layer. (C) 1995 American
Institute of Physics.