Special issue  

Aquifers offer the possibility of exploiting geothermal energy. Especially in fractured aquifers, in order to increase the optimal efficiency of installations which use groundwater as a geothermal resource, flow and heat transport dynamics need to be well understood. This study is aimed at deepening the understanding of this topic through heat transport experiments in fractured networks and their interpretation.

This work investigates the possible correlations between the integral scale of the turbulent stratified flows in the atmospheric boundary layer and parameters characterizing topological features of the wind velocity field, such as fractal dimension and its stability properties, studied through the bulk Richardson number. Fractal dimension and the integral scale of the horizontal (u') and vertical (w') velocity fluctuations have been calculated using the mean wind direction as a framework.

Heating experiments carried out in a limestone quarry close to Paris have shown a classical shape of temperature distribution in steady-state plumes in averages over 24 h, along with rich dynamics of heat flow with intermittent trains of oscillations, spatially coherent, of large amplitudes and a ~ 400 s period, separated by relative quiescence whose duration can reach several hours. The observed behavior could be a universal feature of some turbulent plumes in real geophysical environments.

In this contribution the wind jet dynamics in the northern margin of the Ebro River shelf (NW Mediterranean Sea) are investigated using coupled numerical models. The study area is characterized by persistent and energetic offshore winds during autumn and winter. However, the coupling effect in the wind resource assessment may be relevant due to the cubic relation between the wind intensity and power.

Helical structures are commonplace in geophysical flows, but their effect on turbulence is still enigmatic. A novel PIV laser technique has been used to analyze helical structures in a turbulent swirling jet where the underlying shear flow is subjected to external acoustic forcing. Although the acoustic excitation had an effect on the flow field, no evidence for the existence of large-scale helical structures with maximal helicity was found.

The focus of this paper is to improve our studies related to the novel use of the Thorpe method applied to atmospheric boundary layer (ABL) using new data from Spanish field experiments. We analyse the time behaviour of the maximum Thorpe displacement (d_T)_max and the Thorpe-scale L_T during a day cycle. We also analyse the relation between (d_T)_max and L_T. We deduce that they confirm a power law statistically significant, with differences between convective conditions and shear-driven conditions.

In this paper, a turbulent ocean is modelled in the laboratory. The rotation of the Earth around its axis is represented by the rotation of a turntable. Similar to that in the Earth's ocean, the currents in the laboratory "ocean" are created by density effects when the water is heated or made salty. The laboratory currents are measured by a system which is not unlike the satellite altimetry system used by oceanographers to create "topographic" maps of the elevation of the water surface.