Pressure surge and blade torque during shutdown of in-pipe drag-based turbines.

Hydraulic transients in drag-based in-pipe turbines during sudden operational changes can induce pressure pulsations, water hammer, cavitation, and column separation in pipeline components located both upstream and downstream of the turbine. Additionally, the torque imposed on turbine blades is a critical concern, as frequent operational changes can accelerate blade fatigue and potentially lead to structural failure. This study integrates the Method of Characteristics (MOC) and Computational Fluid Dynamics (CFD) to model transient phenomena resulting from the abrupt stoppage of a hydrodynamic in-pipe turbine. The analysis evaluates how varying deceleration rates influence pressure surges, pressure pulsations, and torque amplification on blades across different blade counts. The results demonstrate that stoppage time significantly affects torque escalation and confirm that turbine blade count strongly influences the magnitude of pressure surges during transient events. Detailed scenario analyses further reveal that specific configurations exhibit greater susceptibility to extreme pressure fluctuations, thereby creating substantial operational and reliability challenges.