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The utilization of pump as turbines (PATs) within water distribution systems for energy regulation and hydroelectricity generation purposes has increasingly attracted the energy field players’ attention. However, its power production efficiency still faces difficulties due to PAT’s lack of flow control ability in such dynamic systems. This has eventually led to the introduction of the so-called “variable operating strategy” or VOS, where the impeller rotational speed may be controlled to satisfy the system-required flow conditions. Taking from these grounds, this study numerically investigates PAT eventual flow structures formation mechanism, especially when subjected to varying impeller rotational speed. CFD-backed numerical simulations were conducted on PAT flow under four operating conditions (1.00 QBEP, 0.82 QBEP, 0.74 QBEP, and 0.55 QBEP), considering five impeller rotational speeds (110 rpm, 130 rpm, 150 rpm, 170 rpm, and 190 rpm). Study results have shown that both PAT’s flow and pressure fields deteriorate with the machine influx decrease, where the impeller rotational speed increase is found to alleviate PAT pressure pulsation levels under high-flow operating conditions, while it worsens them under part-load conditions. This study’s results add value to a thorough understanding of PAT flow dynamics, which, in a long run, contributes to the solution of the so-far existent technical issues.

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The adoption of Pump as Turbines (PATs) both in small scale hydroelectric plants and water supply systems has brought different advantages, the most recognized being cost-effectiveness as compared to other hydroturbines. However, due to their lack of flow control ability, their intolerance to off-design operations constitutes one tough shortfall. Moreover, this technology’s newness leads to PAT flow dynamics still being ununderstood even to date. Therefore, this study intends to numerically investigate the mixed flow PAT’s pump mode flow dynamics for five operating conditions expanding from optimum (1QBEP) to deep part-load (0.41 QBEP) conditions. Moreover the effect of runner blade angle on the same has been investigated where three angles namely -2°, 0°, and 2° have been considered. PAT flow stability was found to deteriorate as the flow decreased, where associated pressure pulsation level worsened at different flow zones. In addition, the blade angle increase led correspondingly increasing flow unsteadiness and pressure pulsation levels, where the pulsation frequencies from rotor-stator interactions were dominant for most of flow zones. This study’s findings are of a crucial importance to both scientific and engineering communities as they contribute to thorough understanding of PAT flow dynamics.

The induction faucet has been widely used in public due to its advantages of convenience, sanitation, water, and electricity saving. To solve the problem of environmental pollution caused by dry batteries used in induction faucets, a suitable micro pipe mixed-flow turbine installed in a tap-water system with only 15 mm in diameter, that uses the pipeline water pressure to generate electricity for the induction faucet was designed and developed, based on computational fluid dynamics (CFD) and model tests. According to the specific speed, a preliminary design of each flow component of the turbine was first produced. Then, using the multi-objective orthogonal optimization method, the optimum test schemes were determined, and the influence of various test factors on the turbine’s hydraulic performance was revealed. Under the design flow rate, the turbine’s power output and efficiency were 6.40 W and 87.13%, respectively, which were 34.45% and 4.99% higher than those of the preliminary scheme. Both the power output and efficiency of the optimized turbine met the design requirements. Numerical and model test results showed good agreement, where the deviation in turbine power output predictions was below 5% under large flow condition. Model test results also showed that the turbine can be started as long as the inlet flow is greater than 0.14 kg/s. Overall, the micro-pipe turbine designed in this paper exploits the (mostly wasted) water kinetic energy in induction faucets for power production, contributing to environmental pollution reduction and realizing energy conservation.