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Abstract Multiphase pump is widely applied for the exploitation of oil-gas resources in off-shore platforms. It is essential to investigate the performance of multiphase pumps when handling high viscosity fluid. A three-stage helico-axial multiphase pump with working fluids under various viscosities is investigated in the present study. Both energy performance and flow fields have been discussed with different viscosities. The influences of viscosity, flow rate and blade height on the distribution of turbulence kinetic energy are analyzed. Results show that both pump head and efficiency gradually reduce with the rise of viscosity when handling high viscosity fluid. The rise of viscosity and blade height, and the decline of flow rate will lead to an increase of turbulence kinetic energy. Characteristics of partial differential equations are employed to reveal the influence of viscosity, and a theoretical model has been established to predict the influence of flow rate.

Abstract Recent studies have coupled blade element momentum (BEM) theory with the Reynolds Averaged Navier–Stokes equations in computational fluid dynamics (CFD) software, as the BEM-CFD method to analyse the flows in marine current turbines is with much less computational resources. The accuracy of the BEM-CFD calculation was evaluated by analysing the performance and flow field characteristics of an isolated horizontal axis marine current turbine with comparisons to a full rotor geometry simulation and experimental data. The comparisons show that the full rotor geometry simulation gives good predictions near the optimal conditions (TSR = 5–7), but is less accurate for off-design conditions. The BEM-CFD results, which are based on two-dimensional hydrofoil theory, are evaluated using the experimental and numerical lift and drag coefficients. It shows that the two-dimensional lift and drag coefficients had significant effects on the BEM-CFD predictions. Overall, the BEM-CFD based on the numerical hydrofoil data can accurately predict the thrust, but generally overestimates the power. The influence of the lift and drag terms on the BEM-CFD predictions suggest that more reasonable 2D predictions for hydrofoils and the 3D effects should be considered to improve the BEM-CFD accuracy. BEM-CFD can reasonably reflect the circumferential averaged velocity characteristics near the rotor for the optimal condition (TSR = 6) and gets symmetrical features in the wake, but it cannot predict the detailed flow features caused by the finite number of blades due to the limitations of the BEM-CFD method.

Abstract Solar energy has developed rapidly in recent years, and its impacts on climate have been revealed mainly through model simulations and limited field observations. However, the representation of solar plants in these models is highly simplistic and does not account for dynamical effects, which may pose risks under the simulations for tracking photovoltaics (PV). To make a more comprehensive assessment of the PV-induced climatic impacts, it is relevant to further develop a more sophisticated PV module based on the observed PV-induced impacts from specific cases. To remedy the deficiencies in the existing PV energy models, the newly sophisticated PV module established in this paper includes both the land surface radiation balance, sensible heat balance and the surface physical dray process over the locations of PV plants. It is then used to simulate the local climatic impacts of PV plants through three parallel sensitivity experiments. Comparison analysis between control run and two PV installation scenarios showed obvious changes in the 10-m wind speed, land surface temperature, and 2-m specific humidity were found locally over the locations of PV plants during both the warm and cold periods. The magnitudes of these changes are positively related to the installed capacity of the PV plants, but are much smaller than the natural climate variations. It is expected that the observation-based PV module established in this paper is a meaningful attempt for the model simulation on this field.

Abstract The S-shaped characteristics of the pump-turbine may cause instability and thus leads to difficulties in grid synchronization. This paper develops a complete model for a pumped storage power plant and studies the start-up and grid synchronization procedure of two 300 MW variable speed units at no load in turbine mode. Based on the grid-voltage-oriented vector control method, the stator voltage of the doubly-fed induction machine is controlled to meet the grid connection requirements. Compared with the fixed speed units, the simulation results show that for a pump-turbine with typical S-shaped characteristics, the fixed speed unit cannot meet the grid connection requirements due to the unstable unit speed. Whereas, the variable speed unit can quickly reach synchronization with the grid voltage. For a pump-turbine without typical S-shaped characteristics, the synchronous unit can meet the grid connection requirements, but it takes a longer time and the stator voltage is not stable enough, while the variable speed unit is 11 times faster and more stable. The effects of PI parameters on the synchronization process of a variable speed unit are also studied. The results show that with suitable PI control parameters, the synchronization process can be accelerated without large overshoot of the rotor power.

Abstract In order to identify impacts of photovoltaic (PV) power plant on surface radiation, this paper conducted a comparative study on the surface radiation and surface albedo characteristics between the PV site and reference site in the Gobi area in Xingjiang, China in the summer of 2020. The results show that, the upward long-wave radiation at the PV site was significantly lower than that at the reference site in the night, while the two were basically the same during the daytime. The average surface albedo at the PV site (0.14) was 39.1% lower than that at the reference site (0.23). Net radiation was higher at the PV site than that at the reference site throughout the whole day. The average net radiation of the underlying surface at the PV site was 30.7% more than that at the reference site, 75% of which was contributed by lower upward shortwave radiation and 25% was due to nocturnal lower upward longwave radiation at the PV site.