We present simultaneous two-dimensional velocity and scal
ar concentrations measured
on a central vertical plane in a turbulent plume. We use an edg
e-detection algorithm to
determine the scalar plume edge, and compare the data obtain
ed in both a fixed Eulerian
frame and relative to local plume coordinates defined in term
s of the instantaneous plume
edge. We observe that the time-averaged distributions of ve
rtical and horizontal velocity
are self-similar. Measurements in the plume coordinate sho
w that there is significant
vertical flow outside the edge of the plume, contrary to the cl
assical notion of purely
horizontal velocities at the plume edge. We observe large va
riations in the plume width
and reason these to be due to the passage of large coherent edd
ies. The flow within the
plume and in the nearby ambient fluid depends on whether an edd
y is present or absent.
When an eddy is present and the plume is wide, the vertical vel
ocities near the plume edge
are small, but in regions where the plume is narrow and there i
s no eddy, large vertical
velocities are observed outside the plume.