This paper describes the experimental study of a behavioural barrier consisting of a bubble curtain placed near an ecological river water intake, aiming to assess the bubble curtain’s influence on the velocity field of water flowing in the water intake proximity. The scientific novelty is given by the water intake solution operating in tandem with the dedicated bubble curtain generator used for avoiding fish entrapment. The water intake solution used in the present research is based on a run-of-river intake without a dam in the riverbed, maintaining the mountain rivers longitudinal connectivity. An experimental setup was designed and built to study the behavioural barrier for ecological water intakes in different operating conditions. Thus, tests were performed for two water velocities (0.33 m/s and 0.535 m/s) in the experimental setup, two water depths (92 mm and 119 mm) and two air flow rates (10.5 LPM and 15 LPM). The results were compared with the case when no air is injected through the bubble curtain generator. The assessment of the bubble curtain influence on the water flow inside the channel was made by measuring and analysing the velocity variation in vertical and horizontal direction. The results showed a significant velocity gradient in the bubble curtain proximity, which can contribute to influencing the behaviour of the fish by deterring them from the water intake area.

Different scenarios of an arch-dam breach and their impact on the time-space evolution of flood waves are analysed using numerical modelling. As the accidents involving this type of dam are among the most catastrophic ones, the 108 m in height Paltinu arch-dam, Romania, was chosen as a case study due to its problems in the past. Three dam breach magnitudes and two inflow hydrographs for the worst-case scenario of Normal Operating Pool elevation in the reservoir were chosen as variable parameters, to assess their influence on the dam break wave characteristics and downstream flooded areas. The flood was routed along the 18 km reach of the Doftana River down to the confluence with the Prahova River. A 2D numerical model was set up with the help of HEC-RAS software, which was also used to analyse the resulting hazard maps under a GIS environment. Comparison of inundation boundary, maximum depths and velocities, as well as the arrival time at control sections allow for conclusions to be drawn. These predictive results of shape, magnitude, and time to peak of the flood waves are essential for flood risk management to obtain the risk maps, estimated damage costs, and possible affected areas.

A small Savonius wind turbine of helical type was tested in an open jet wind facility for identifying the optimum position of the rotor blades aiming the maximization of static torque. The two blades of the wind turbine of U shape were twisted up to 180⁰ from bottom to top and three values for blade overlap were considered i.e. 0.35, 0.2 and 0.0. The turbine torque was measured for no load conditions and wind velocities between 2-8 m/s. In the same time the air flow through Savonius rotor was observed by using a visualization setup aiming to identify the correlation between the torque and the flow pattern inside the returning blade at rotating angles where the torque has highest values. Best results for the torque coefficient of 0.72 and power coefficient of 0.265 were obtained at a wind velocity of 5.8 m/s and low overlap ratio of 0.2. By measuring the overall torque of the rotor for each case study, the positive effect of pressure recovery was explained as a result of air flow through the blade overlap from the concave side of the advancing blade to concave side of the returning blade for a certain interval of the rotating angle a = 50-60°.

Wind energy represents one of the main sources of renewable energies. Innovation in wind turbine technology tends to focus on increasing energy production, especially at low wind velocities. Vertical axis wind turbines could have a greater expansion because they have many advantages, such as the capacity to start at low wind velocities and no need for orientation to the wind direction. The present paper analyses numerically and experimentally, a Savonius-Darrieus hybrid wind system on a common vertical shaft. CFD modeling and simulation show a slight instability at low velocities, up to entering the nominal working regime of 2-3 m/s, but also the separation of vortices and the fluid-blade interaction at over 9 m/s. At higher velocities, the performances and the power coefficients decrease, observations demonstrated also experimentally within the study. The optimal wind velocity for the Savonius-Darrieus vertical turbine is 6 m/s.

In order to increase the interval between cleanings of a hollow fiber membrane bundle (HFMB) used for water ultrafiltration, a numerical study and an experimental test were conducted. The relation between the water flow rate and shear stress along the hollow fiber membrane wires (HFMW) was studied for three geometries. Three angles (α = 90⁰,45⁰,0⁰) for the intake flow pipe (d_i = 25 mm) against the horizontal axis of a cylinder (D_c = 100 mm; L = 600 mm) containing one hollow fiber membrane wire (d_w = 1 mm) were chosen for the numerical investigation; five different water flow rates (Q = 8…16 l/min) were considered. The values for the shear stresses along one membrane wire placed along the cylinder's central axis were computed. The findings show that the best geome1try for enhanced shear stress is obtained for α = 0⁰. For this geometry a mean value of 1.1 Pa for the shear stress was obtain along the first 1/3 of the membrane wire at a minimum flow rate of Q = 8 l/min. Higher values for water flow rates do raise shear stress but increased energy consumption is needed. The tests were carried out on a HFMB with molecular weight cut-off (MWCO) of 0.097 μm, that was put in a glass cylinder with a horizontal axis, for μ = 900, μ = 00, and Q = 8 l/min. The results confirmed the conclusions of the numerical study i.e. the filtering capacity of the membrane was maintained higher by 6-6.5% for α = 0⁰ comparing to α = 90⁰ due to shear stress increase. For the flow rate of Q = 12 l/min the filtering capacity of the membrane did not increased. The study confirmed the hypothesis that for certain geometries there could be settle down optimum flow rates to minimize energy consumption during membrane operation but comprehensive research is needed.