Effects of blade solidity on the transient start-up characteristics of pipeline-type spherical hydraulic turbine

The pipeline-type spherical hydraulic turbine is an emerging residual pressure recovery device that aligns with the development needs of smart urban water management. However, in practical industrial applications, due to the uncertainty of water flow, hydraulic turbines may experience frequent start-stop cycles. If the start-up performance of the hydraulic turbine is poor, adding auxiliary start-stop equipment will make the generator module more complex. Furthermore, blade solidity is considered a key factor affecting the start-up performance of spherical hydraulic turbines.Therefore, This study employs the Six-Degree-of-Freedom (SDOF) solver to investigate the transient start-up characteristics of Spherical hydraulic turbines with different chord lengths and blade numbers. Experimental validation was conducted to affirm the reliability of numerical simulations using SDOF solver. Through numerical simulations, it was determined that there exists an optimal chord length for pipeline-type Spherical hydraulic turbines under unloaded conditions, ensuring their optimal start-up performance. Subsequently, based on this optimal chord length, the impact of different blade numbers on the start-up performance of pipeline-type Spherical hydraulic turbines was assessed. The study revealed that the best start-up performance is achieved when the chord length is c/d = 0.2 and the blade count is N = 5. This research provides valuable insights for the engineering application of pipeline-type Spherical hydraulic turbines.