This thesis presents an investigation into kinematic features of fine scale turbulence in free
shear flows. In particular it seeks to examine the interaction between the different length scales
present in shear flow turbulence as well as the interaction between the strain-rate tensor and
the rotation tensor, which are the symmetric and skew-symmetric components of the velocity
gradient tensor respectively.
A new multi-scale particle image velocimetry (PIV) technique is developed that is capable
of resolving the flow at two different dynamic ranges, centred on inertial range scales and on
dissipative range scales, simultaneously. This data is used to examine the interaction between
large-scale fluctuations, of the order of the integral scale, and inertial and dissipative range
fluctuations. The large-scale fluctuations are observed to have an amplitude and frequency
modulation effect on the small scales, and the small scales are shown to have a slight effect on
the large scales, illustrating the two way nature of the energy cascade. A mechanism whereby
integral scale rollers leave behind a wake of intense small-scale fluctuations is proposed.
The interaction between strain and rotation is examined with regards to the rate of enstrophy
amplification (ωiSijωj). It is found that the mechanism that is responsible for the
nature of enstrophy amplification is the alignment tendency between the extensive strain-rate
eigenvector and the vorticity vector. This mechanism is also observed to be scale dependent for
ωiSijωj > 0, but independent for ωiSijωj < 0. This is subsequently confirmed with new dual-plane
stereoscopic PIV experiments performed as part of this study. Finally, computational
data is used to examine the effect of experimental noise and variation of spatial resolution on
the observation and understanding of this strain - rotation interaction
