Abstract-
In this talk I will give an overview of our work that is aimed at investigating
the characteristics of dissipation structures in gas-phase turbulent jet flows.
Particle image velocimetry and planar laser-induced fluorescence of acetone
vapor are used to obtain simultaneous images of the 2-D velocity and conserved
scalar fields. The jet facility was specifically designed to enable us to
obtain well-resolved measurements of the finest scales of turbulence.
An important outcome of this work is that we have developed a procedure to
quantify the effects of optical-system blur on the measurements of flow
scalars and scalar gradients.
A major issue that will be discussed is whether the finest scales of turbulence
are best represented by the Kolmogorov / Batchelor scales or whether the finest
scales are in fact several times larger, as has been suggested by some
researchers. Our measurements are sufficiently well resolved that a definitive
statement can be made in this regard. In addition we are interested in
understanding the relationship between the scalar dissipation structures and
kinematic quantities such as strain rate and vorticity. We explore this
relationship both instantaneously and statistically, and we show that a simple
unsteady strained laminar diffusion-layer model works remarkably well in
capturing the gross features of the dissipation-strain relationship measured
in turbulent flows.