The Small-Scale Structure of Dispersing Clouds in the Atmosphere.
Abstract
The fractal properties of a plume dispersing in a turbulent velocity field have been examined using Large-Eddy Simulation results for neutral and convective boundary layers. A fractal generation technique has been developed that correctly matches a specified mean and variance distribution for the plume. The spatial correlation scale of the fractal realizations can also be specified, and the one-point probability density function can be chosen as clipped normal or lognormal. Realizations generated with the fractal technique show reasonably close resemblance to the LES results. The small-scale structure of the plume is further analyzed using multifractal techniques, and a the generation methodology is extended to incorporate unequal partitioning of the random variance during the refinement process. This procedure corresponds to the localization of small-scale energy in the turbulent cascade process which leads to an intermittent dissipation field. The multifractal spectrum of the dissipation field can be adjusted to match observations and the LES calculation results. The visual appearance of the dissipation field from the fractal/multifractal model is much more intermittent than the fractal realization, and the concentration field shows more localized small-scale fluctuations. These features give better correspondence to the LES realizations.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1994
- Accession Number
- ADA288256
Entities
People
- Douglas S. Henn
- R. I. Sykes
- Robert S. Gabruk