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y Coanda-flapping of the free shear layer. The particles (light spots on
centreline, dark spots just off centre-line of the rig) have a fall speed of
0.034m/s and the depth-averaged flow speed is 0.31m/s.
Figure 4. The plates show three views of the recirculation region behind an
experimental bedform. The shots are 0.35 sacs, apart and clearly visualise
the sweeping away of the turbulent region, leading to re-attachment close to
the trough. We term this sequence of events Coanda-flapping.
Figure 5. Intervals between Coanda-flapping events, between the passage of
strong shear layer vortices (SLVs) and between other turbulent events at
U=0.20m/s. There is a strong correlation between the Coanda-flapping events
and the passage of upstream turbulent events.
Figure 6. Intervals between Coanda-flapping events and between the passage
of turbulent events, including shear layer vortices, at U=0.31m/s. This
highlights the fact that not all upstream turbulence can trigger the Coandaflapping
event.
Figure 7. The intervals between Coanda-flapping events and between strong
shear layer vortices at U=0.36m/s.
Figure 8. The intervals between Coanda-flapping events at various values of
inter-crestal spacing L-nLo where n=1.0, 1.5, 2.0, 2.5, 3.0 at U=0.43m/s.
Notice the peak occurs in the 2.5s interval range for L=3.0Lo rather than the
1.5s interval range.
Figure 9. The interval(s) between Coanda-flapping events plotted against the
cumulative sum of the intervals for inter-crestal spacing L=Lo. The point
with the lowest gradient is the modal interval which can be seen on the graph
below, indicated by the dotted lines.
Figure 10. The gradient of the line in the above figure averaged over eleven
neighbouring points so as to remove the peaks and troughs where only two or
xi