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nor the outer layer solely responsible for turbulent energy
production: but rather ascribing this process to their
interaction.
Grass (1971) reported on extensive experiments using smooth and
rough walls (u*k/u=0.0, 20.7, 84.7; k is the roughness height)
and found that ejections and inrushes remained unchanged. Offen
& Kline (1974) proposed a kinematic description of the link
between the inner and outer flow, hypothesising that pairing of
vortices associated with two to four bursts led to bulges in the
superlayer. Kovasznay et al (1970) were the first to notice the
saddle point on the upstream facing (rear) side of the outer flow
bulges at a height of y/6 = 0.8 when seen in a reference frame
convected with the flow.
Antonia & Bisset (1990), used a spanwise array of hot wires to
detect bursts and sweeps, and found that the streamwise length
of a sweep was about twice that of a burst, with a value of about
960 wall units at y*=15. The spanwise extent of a sweep was
about 25% larger than that of a burst.
Both the length and width of sweeps and bursts were found to
increase with distance from the wall and contours of with
9/3x and d/dz showing the presence of a three dimensional
shear layer associated with the end of the burst phase and
marking the probable interface between a burst and a sweep. They
also found that the largest values of instantaneous du/dz were
comparable with those of the mean velocity gradient at the wall.
Al-4