Study on performance of an asynchronous reverse-type combined vertical axis hydrokinetic turbine
A novel design featuring a combined vertical axis hydrokinetic turbine,incorporating asynchronous reverse rotation of inner and outer rotors,was proposed to overcome the issue of low static torque,a limitation that restricts the use of lift-type vertical axis hydrokinetic turbines in low-speed marine environments.This combined turbine incorporates asynchronous reverse rotation of inner and outer rotors,where the external rotor is an H-type,while the internal rotor adopts the Savonius configuration.This arrangement ensures that both rotors operate at their optimal tip speed ratios,thereby maximizing operational efficiency while reducing the startup flow velocity of the system.Computational fluid dynamics software was employed to analyze the influence of the tip speed ratio of the internal rotor and the diameter ratio of the combined turbine on the performance of the external H-type rotor and the combined turbine.The static torque coefficient of the combined turbine at different flow angles was investigated by the numerical calculation method.The results show that when the diameter ratio is less than 0.4,variations in the tip speed ratio of the internal rotor have minimal impact on the efficiency of the external H-type rotor.However,as the tip speed ratio of the internal rotor exceeds 0.5,it starts to consume more power,resulting in a decrease in the overall system efficiency.Additionally,flow field analysis reveals that due to the differing rotational speeds of the internal and external rotors,a higher diameter ratio in the combined turbine leads to pronounced phase interference between the two rotors.This interference causes increased torque fluctuations in the external rotor and shortens the operational lifespan of the device.Therefore,a diameter ratio ranging from 0.2 to 0.4 and a tip speed ratio of the internal Savonius rotor between 0.2 and 0.5 are recommended.The combined turbine exhibits a significant increase in static torque coefficient in most flow directions.
万方数据
维普
