Structural analysis of a very low-head axial hydro turbine

Abstract

This article presents the structural analysis of a newly designed very low-head hydraulic turbine with a tip diameter of 4.5 m. It can accommodate large discharges up to 22.87 m³/s to generate electricity from an irrigation canal near a rural community in Ethiopia. For the first time, the structural integrity of a very low-head turbine is investigated by employing well established methods from fluid dynamics and structural dynamics. Methodologically, static structural and vibroacoustic analyses were performed in vacuum and water to identify the respective mode shapes and eigenfrequencies. The static pressure from prior computational fluid dynamics simulations was mapped onto the runner structure to examine the static stress distribution through finite element analysis. The unsteady pressure field was also assessed to estimate the dynamic stress level and the risk of resonance in the turbine runner under the expected loading conditions. The findings reveal that there are no significant failure risks associated with static stresses or fatigue induced by dynamic stresses. Safety factors of 13.3 and 88 were obtained for static and dynamic stress, respectively, using structural steel as the runner material. Moreover, understanding the structural behavior of very low-head turbines is enhanced by identifying the various vibration mode shapes and eigenfrequencies. The eigenfrequencies reduction ratio in water relative to vacuum was found to be between 37.43 % and 31.82 % for the first ten modes, which aligns well with results from conventional hydraulic turbines. Overall, the results pave the way for the safe deployment of this turbine at a pilot site, providing electricity and marking a significant milestone towards the widespread adoption of this technology. This way, the nation's abundant hydropower resources in existing hydraulic structures and rivers can be harnessed.