This work extends the study of the structure of wall-bounded flows
using the
topological properties of eddying motions as developed by Chong et
al. (1990),
Soria et al. (1992, 1994), and as recently extended by Blackburn
et al. (1996) and Chacin et al. (1996). In these works,
regions of flow which are focal in nature are identified by
being enclosed by an isosurface of a positive small value of the discriminant
of the
velocity gradient tensor. These regions resemble the attached vortex loops
suggested
first by Theodorsen (1955). Such loops are incorporated in the attached-eddy
model
versions of Perry & Chong (1982), Perry et al. (1986),
and Perry & Marusic (1995),
which are extensions of a model first formulated by Townsend (1976). The
direct
numerical simulation (DNS) data of wall-bounded flows studied here are
from the
zero-pressure-gradient flow of Spalart (1988) and the boundary layer with
separation
and reattachment of Na & Moin (1996). The flow structures are examined
from the
viewpoint of the attached eddy hypothesis.