Turbulent structure in environmental flows: effects of stratification and rotation

Abstract

Several series of experiments in stratified and in rotating/stratified decaying flows after a grid is used to stir the two layer stable fluid
 brine and fresh water set up. We measure by comparing the gained potential energy with the available kinetic energy AKE, the
 relative efficiency of mixing. The experiments in stratified rotating flows with grid driven turbulence were both periodic (quasi
 stationary) and non-monotonic (decaying) forcing. This thesis compares experimental, numerical and field observations on the
 structure and Topology of the Stratified Rotating Flows as well as their decay, the horizontal spectra changes appreciable with
 slopes from 1.1 to 5, but vorticity and local circulation, and also the initial topology and forcing of the flow.
 A detailed study of the vorticity decay and vortex and energy structure has been performed, the new results show that neither
 stratified nor rotating flows exhibit pure 2D structures. The work parameterizes the role of the Richardson number and the Rossby
 number, both in the experiments and in the ocean visualizations is very important. The conditions of vortex decay show the effects of
 the internal waves in the decay turbulent conditions both for stratified and rotating flows. The parameter space (Re,Ri,Ro) has been
 used to interpret many previously disconnected explanations of the 2D-3D turbulent behaviour. The comparison of numerical
 simulations with experiments has allowed implementing new theoretical aspects of the interaction between waves and vortices
 finding the surprising and very interesting result that these interactions depend on the level of enstrophy. This also leads to new
 ways of using multifractal analysis ad intermittency in ocean environmental observations.
 A large collection of SAR images obtained from three European coastal areas were used for routine satellite analysis by SAR and
 other sensors, which seem very important to build seasonal databases of the dynamic conditions of ocean mixing. The topology of
 the basic flow is very important and in particular the topology of the vortices and their decay which depends on ambient factors such
 as wave activity, wind and currents. We find more realistic estimates of the spatial/temporal non-homogeneities (and intermittency
 obtained as spatial correlations of the turbulent dissipation); these values are used to parameterize the sea surface turbulence, as
 well as a laboratory experiments at a variety of scales.
 Using multi-fractal geometry as well, we can establish now a theoretical pattern for the turbulence behaviour that is reflected in the
 different descriptors. Vorticity evolution is smoother and different than that of scalar or tracer density. The correlation between the
 local Ri and the fractal dimension detected from energy or entropy is good. Using multi-fractal geometry we can also establish
 certain regions of higher local activity used to establish the geometry of the turbulence mixing that needs to be studied in detail when
 interpreting the complex balance between the direct 3D Kolmogorov type cascade and the Inverse 2D Kraichnan type cascade.