Resolution Requirements for Scalar Dissipation Measurements in Turbulent Jets and Flames.
Resolution Requirements for Scalar Dissipation
Measurements in Turbulent Jets and Flames.
Pitts, W. M.
Annual Meeting, 52nd. Proceedings. American Physical
Society/Division of Fluid Dynamics. November 21-23,
1999, New Orleans, LA, 37-37 pp, 1999.
turbulent jet flames; scalar dissipation
Scalar dissipation, defined as twice the product of the
molecular diffusion coefficient and the Iocal gradient
of the mixture fraction do&d with itself, characterizes
molecular mixing rates in turbulent flows and has a
central role in turbulent combustion modeling.
Experimental measurements require sufficient resolution
to ensure that the local scalar gradient is effectively
constant in time and space. Traditionally, it was argued
that it was necessary to resolve spatial features on the
order of size of the Batchelor scale, the product of the
Kolmogorov scale and the inverse square root of the
Schmidt number, which are typically a few hundred
micrometers for laboratory flows. More recently, it has
been suggested that the required spatial resolution may
be 12-25 times larger than the Batchelor scale.
Relaxation of the resolution requirements by such large
factors would allow measurements with greatly improved
signal-to-noise ratios. Unfortunately, recent
experiments, including scalar dissipation measurements
along a line in an axisymmetric jet of propane into air
at the National Institute of Standards and Technology,
have shown that the larger estimates for the required
spatial resolution will result in partial averaging of
the scalar dissipation. Taken together, the studies
suggest that in order to fully capture scalar
dissipation fluctuations the spatial resolution must be
no larger than 2-3 times the Batchelor scale.