The structure of turbulent jets, vortices and boundary layer: Laboratory and field observations

The main aim of this work is research, understand and describe key aspects of the turbulent jets and effects connected with them such as boundary layer interactions or the effect of a 2D geometry. Work is based principally on experiments but there are also some comparisons between experimental and field results. A series of experiments have been performed consisting in detailed turbulent measurements of the 3 velocity components to understand the processes of interaction that lead to mixing and mass transport between boundaries and free shear layers. The turbulent wall jet configuration occurs often in environmental and industrial processes, but here we apply the laboratory experiments as a tool to understand jet/boundary interactions in the environment. We compare the structure of SAR (Synthetic Aperture Radar) images of coastal jets and vortices and experimental jets (plumes) images searching for the relationship between these two kinds of jets at very different Reynolds numbers taking advantage of the self-similarity of the processes. In order to investigate the structure of ocean surface detected jets (SAR) and vortices near the coast, we compare wall and boundary effects on the structure of turbulent jets (3D and 2D) which are non-homogeneous, developing multifractal and spectral techniques useful for environmental monitoring in space

Relationship between intermittency and stratification

A formal analogy exists between 2D turbulence and 3D turbulence with stratification and rotation. Although the effect of the rotation, to the scale typical of the turbulence, is negligible in the atmosphere, we have found a relationship between the behavior of the intermittency and that of the atmospheric stratification. In order to do that, the intermittency has been characterized through the flatness of the PDFs of velocity increments, for the smallest possible scale, present in our measurements

Experiments in stratified and rotating decaying 2D flows

Two sets of turbulence decaying experiments have been performed, with the aim of focusing in the middle of a strongly stratified density interface. The experiments have been done under two different external conditions: a) stirring (non-rotating) decaying 2D turbulence experiments and b) rotating decaying 2D turbulence experiments. Non-rotating experiments were performed in a 1×1m tank, while the rotating experiments were performed in a rectangular tank of 4×2m; this rectangular tank was placed in the middle of the Coriolis rotating platform from the Trondheim Marine Systems Research Infrastructure supported by the European Community TMR Project. The set of stirred experiments is a compilation of five series of mixing experiments, dependent on the initial interfacial Richardson number. The total time of mixing was between 53 and 72 minutes. The density of the brine used in the experiment after was between 1027 and 1037 kgm−3. The boundary conditions for all the rotating experiment are related to initial Reynolds Rer, Rossby Ro, Ekman Ek and Richardson gradient Rig numbers, the results are summarized and presented in a 3D parameter map using potential relationships

Optimized sound diffusers based on sonic crystals using a multiobjective evolutionary algorithm

Sonic crystals have been demonstrated to be good candidates to substitute for conventional diffusers in order to overcome the need for extremely thick structures when low frequencies have to be scattered, however, their performance is limited to a narrow band. In this work, multiobjective evolutionary algorithms are used to extend the bandwidth to the whole low frequency range. The results show that diffusion can be significantly increased. Several cost functions are considered in the paper, on the one hand to illustrate the flexibility of the optimization and on the other hand to demonstrate the problems associated with the use of certain cost functions. A study of the robustness of the optimized diffusers is also presented, introducing a parameter that can help to choose among the best candidates. Finally, the advantages of the use of multiobjective optimization in comparison with conventional optimizations are discussed.This work was partially supported by the Spanish "Ministerio de Economia y Competitividad" under the projects TEC2015-68076-R and DPI2015-71443-R.Redondo, J.; Sánchez Pérez, JV.; Blasco, X.; Herrero Durá, JM.; Vorlander, M. (2016). Optimized sound diffusers based on sonic crystals using a multiobjective evolutionary algorithm. Journal of the Acoustical Society of America. 139(5):2807-2814. doi:10.1121/1.4948580S28072814139

An experimental model of mixing processes generated by an array of top-heavy turbulent plumes

The mixing process of two fluids of unequal density generated by the evolution of an array of forced turbulent plumes is studied in the laboratory. The corresponding qualitative conclusions and the quantitative results based on measures of the density field and of the height of the fluid layers are described. The partial mixing process is characterized and analyzed, and the conclusions of this analysis are related to the mixing efficiency and the volume of the final mixed layer as functions of the Atwood number, which ranges from 0.010 to 0.134. An exponential fit is used to evaluate the mixing efficiency versus the Atwood showing the role of initial conditions on mixing efficiency variability

Induced structures under seasonal flow conditions in the Ebro delta shelf. Laboratory and numerical models

The characteristic induced length scale produced by a river flow in its outlet is studied. Two experimental methods are compared: a) Physical modeling in laboratory and b) numerical mesoscale diffusion model; under low tidal and realistic seasonal flow conditions from Spring, Summer, Fall and Winter field data from the Ebro delta shelf. The physical laboratory experiences were performed on a five-meter diameter turntable, using the Froude-Rossby similarity. This paper shows complementary results from both methods investigating the vortex characteristic and the dynamics of the flow. The experimental results under rotating conditions show coherent vortex dynamics in the large-meso scale coastal boundary. The numerical model, on the other hand, lacks the mesoscale vortex dynamics and its induced diffusion but gives reasonable flow conditions in the close region (15–20 km) around the river mouth. Both the experiments and numerical simulations show river plume diffusion smaller than D2 ∝ t3