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The main problems mentioned above are typically studied using large-scale models with a resolution ranging from the order of hundreds of meters to kilometers. Thus horizontal and vertical small scale mixing cannot be directly resolved by the model itself. Local, or smaller-scale, phenomena, however have a strong impact on several environmental problems, including pollution. Such phenomena require a complete three-dimensional analysis of the fluid flow, to evaluate the dominant vortex structure arrangement of the resulting turbulent field.
These small scales are not present in the large scale models described above where they need to be parameterized. Similarly, three-dimensional turbulence in realistic systems still cannot resolve the entire flow field and parameterization of small-scales is a fundamental issue of any study involving turbulence. Indeed, the quality of the results from large-scale models depends on many features, among them a crucial aspect is the capability of the turbulence parameterization to correctly reproduce the small-scale mixing dynamics under complex-flow conditions, such as rotation, stratification and topographic effects.
The choice and, when needed, the improvement and the re-formulation of turbulence parameterization and closures to be used in conjunction with large-scale models require a deep knowledge of the underlying physics including the dynamics of turbulence. Hence, the study of small-scale processes per se, is essential to understand the physical mechanisms of mixing within the fluid, to identify the main drawbacks of the existing schemes, and to adapt or develop, whenever needed, new and more effective models.
An important role in the study of three-dimensional turbulence is played by transport/dispersion phenomena characterized by an interaction between different phases. The typical case is that of two-phase flows, where a diluted phase is transported within a carrying one (for instance water or air). Understanding and modeling transport phenomena is of great importance in may application of fluid dynamics, especially in the environment (dispersion of solid particulates, interaction between turbulence and biological species etc.). The mathematical and physical characterization of these phenomena is the basis for investigating applicative problems.