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Cavitation is recognized as a phenomenon that can cause serious damage to a hydro turbine and can reduce its performance when operating at off-design point. This is an undesired phenomenon, which needs to be improved. In order to suppress the cavitation in the Francis turbine draft tube, a technology with grooved draft tube named J-Groove is introduced in the Francis turbine. The Francis turbine performance and the internal flow characteristic are investigated both with and without J-Groove installation by the experimental method and numerical simulation. Visualization was used to capture the cavitation rope in the Francis turbine draft tube to compare with the computational fluid dynamics analysis result. The results show that the turbine performance both with and without J-Groove installation is quite similar. Regardless of impact on performance of Francis turbine by J-Groove, it suppresses the cavitation vortex rope and pressure fluctuation in the Francis turbine draft tube efficiently. [ABSTRACT FROM AUTHOR]

The pressure fluctuations of the turbines are caused by the swirl component in the draft tube, which is an undesired phenomenon that needs to be improved when the turbine operates in the off-design condition. In order to avoid these kinds of unsteady flow phenomena, a technology of J-Groove on the draft tube wall is investigated by numerical method. The validation test of performance is conducted to compare the result of numerical and experimental methods. The steady and unsteady state analyses are conducted to investigate the internal flow of a Francis hydro turbine model draft tube with and without J-Groove. The swirl flow in the draft tube is significantly suppressed by the J-Groove installation. Moreover, according to the unsteady state analysis, the amplitude of pressure fluctuation in the draft tube is reduced effectively by the J-Groove. [ABSTRACT FROM AUTHOR]

Pumped hydro energy storage systems are a reliable solution for maintaining grid stability. However, the pump turbines utilized in these systems often display instability due to pressure fluctuations, and the draft tube experiences additional fluctuations from the formation of a cavitation and vortex rope. This paper introduces a novel J-groove design method and presents four different designs of J-grooves. Unsteady analysis is performed.The J-grooves reduce the magnitude and alter the distribution of axial and tangential velocities inside the draft tube, which results in the disruption of vortex rope through the generation of jet flow from J-grooves. The grooves exhibit noticeable suppression effects on cavitation, vortex rope and pressure fluctuations, while this comes at the expense of efficiency. J-grooves with uniform thickness significantly suppress pressure fluctuations, while thickening the leading and rear edges respectively benefits the suppression of runner and draft tube cavitation. The cavitation suppression effectiveness of the long-short type J-groove is inferior to the other models, but it incurs lower efficiency losses. These findings provide insights into the suppression of cavitation and vortex rope and are of significant importance for the optimization of J-grooves. • A design approach for controlling the frontage and rear edges of the J-groove has been proposed. • The J-groove mitigates cavitation, vortex rope and pressure fluctuations effectively. • The jet flow induced by the J-groove impacts the axial and tangential velocities. [ABSTRACT FROM AUTHOR]