Pump operation control under variable system demand is obtained either by throttling the discharge pipe, by using by-pass pipes, by modifying the rotor speed, or by separating the pump and the demand by means of a pressurized tank. We try to assess the efficiency of pump operation control by using a numerical model created in EPANET for a 24hours period. To avoid the demand driven algorithm used by EPANET, the network model consists of a throttle control valve followed by an emitter. Pump or valves parameters are modified using control statements. Results are consistent with the general theory

This research presents a numerical investigation of two-phase flow during the expulsion of entrapped air in a non-confined pipe. A modified version of the volume of fluid (VOF) approach is employed considering the effect of compressibility in the liquid. A modification is introduced to the original approach relating the density changes in the liquid to the pressure changes using the fluid bulk modulus. The bulk modulus is also modified to consider the pipe elasticity, the air bubble entrainment and the two-phase flow regime in a pipe. Fluid–structure interaction (FSI) code is developed and used to calculate the motion of the downstream orifice wall during the impact of the water column on the pipe end wall. The numerical results of the pressure variation agree well with experimental data. The two-phase flow structure and physics behind the pressure waves are investigated. The numerical results show that to capture the amplitude and time interval of the pressure surges, the effect of FSI should be considered during the expulsion of the entrapped air. Additionally, the effects of initial air pocket size, supply pressure and orifice size on the pressure increase are investigated. The developed VOF-FSI approach can be employed as a numerical tool to investigate the transient flow during pipe filling.

The environmentally friendly concept in terms of water quality represents a condition for developing hydropower plants all around the world. Since 2017, hydropower has represented more than 70% of all renewable energy production and it is essential for the integration of the other renewable sources of energy and for regulation of the grid. To maintain the “green” label concerning the dissolved oxygen level (6 mg DO/L), the energy suppliers should respond to environmental concerns about the operation of hydropower plants. In the context of sustainable development, the ecological degradation of rivers is unacceptable due to the implementation of a hydropower plant on the watercourse. For deep reservoirs or tropical regions, the oxygen level in the water downstream of the hydropower plants may be low and affect the aquatic life for many kilometers downstream. This paper presents a new aeration system for discharged water from hydropower plants that provides water aeration with minimum energy consumption. The influence of the aeration process on the turbine operation and efficiency is analyzed. Experimental measurements are carried out on site on a small Francis turbine. The influence of the aeration process on the turbine mechanical performances (vibration level and relative displacement) and hydraulic performances (turbine efficiency, power output, and pressure fluctuation) is analyzed. The results showed that the impact of the aeration device implementation and operation over the energetic characteristics of the turbine is in the efficiency measurements accuracy range. The aeration through this device did not influence the turbine operation (vibration, level, or pressure fluctuations).