Jets arising from rivers, streams and tidal flows entering still waters differ
from most experimental studies of jets both in aspect ratio and in the presence
of a solid bottom boundary and an upper free surface. Despite these differences,
the applicability of experimental jet studies to these systems remains largely
untested by either field or realistically scaled experimental studies. Here we
present experimental results for a wall-bounded plane jet scaled to jets created
by flow discharging into floodplain lakes. A characteristic feature of both our
prototype and experimental jets is the presence of large-scale meandering
turbulent structures that span the width of the jets. In our experimental jets,
we observe self-similarity in the distribution of mean streamwise velocities by
a distance of six channel widths downstream of the jet outlet. After a distance
of nine channel widths the velocity decay and the spreading rates largely agree
with prior experimental results for plane jets. The magnitudes and distributions
of the cross-stream velocity and lateral shear stresses approach self-preserving
conditions in the upper half of the flow, but decrease in magnitude, and deviate
from self-preserving distributions with proximity to the bed. The presence of
the meandering structure has little influence on the mean structure of the jet,
but dominates the jet turbulence. A comparison of turbulence analysed at time
scales both greater than and less than the period of the meandering structure
indicates that these structures increase turbulence intensities by 3–5
times, and produce lateral shear stresses and momentum diffusivities that are
one and two orders of magnitude greater, respectively, than turbulence generated
by bed friction alone.
The distortion of crystals of aluminium under compression. Part III.―Measurements of stress
