Fig. 4. Views of the wake in the vertical (XY) plane of an individual of
Scomber japonicus 26 cm in fork length swimming steadily at speeds of
1.2 FLs-1 (A) and 2.2 FLs-1, where
FL is fork length (B). The orientation of the caudal fin to the light
sheet is shown in the diagram. Flow velocity is represented by black vectors
plotted over a color background indicating vorticity. At both swimming speeds,
the caudal fin sheds one pair of counter-rotating vortices with a central jet
of high-velocity flow per stroke. The white arrows and labels in B illustrate
the axes of velocity profiles presented in
Fig. 5. X' is
the longitudinal axis of the ring; Y' is perpendicular to
X'.
