Stator element design investigation for in-pipe applications of a H-Darrieus hydrokinetic turbine

The present work examines the impact of the stator geometry on the performance of an in-pipe H-Darrieus hydrokinetic turbine, with particular attention to its integration within water distribution systems. This study is driven by the growing need for decentralized energy harvesting (EH) solutions capable of supplying power to wireless sensor networks (WSNs), while ensuring reliable operation of the hydraulic infrastructure. A reference configuration was first defined and numerically validated. Subsequently, a series of geometrical modifications were introduced to assess their impact on the flow field and turbine performance. These include: a more compact convergent section (Case 01), variations of the case geometry affecting the blade radial gap and lateral wall inclination (Cases 02, 022, and 023), and an asymmetrical configuration (Case 03) designed to improve flow guidance toward the rotor. The performance of each configuration is assessed through computational fluid dynamics simulations using ANSYS CFX, considering key indicators such as hydraulic efficiency, power coefficient, head requirement, and dimensionless head coefficient. Firstly, each configuration is compared with the reference case, both in terms of numerical and qualitative results; finally, a global comparison of the numerical results is performed for all cases. The obtained results indicate that the convergent section has a negligible impact on the overall system performance, whereas the case and diffuser sections play a dominant role. In particular, the blade radial gap is identified as a key design parameter: its reduction leads to a significant increase in power coefficient (up to approximately +36%), at the expense of a higher head requirement. Additionally, large expansion angles in the case and diffuser sections are found to deteriorate pressure recovery, promoting flow separation and reducing overall efficiency.