CFD optimization of an in-pipe H-Darrieus pico water turbine for energy harvesting applications

Energy harvesting from in-pipe water flows in municipal distribution networks presents a sustainable solution for powering autonomous monitoring systems and wireless sensor networks (WSNs), thereby reducing reliance on battery-powered devices. However, the performance of hydrokinetic turbines in such confined environments remains inadequately described by classical open-flow theories. The present thesis investigates the design and optimization of an in-pipe, pico water, three-blade H-Darrieus turbine using high-fidelity computational fluid dynamics (CFD), implemented within the commercial Ansys software. To this end, a parametric study based on large eddy simulation (LES) is conducted to characterize the turbine's performance. The key design parameters investigated are the rotor blockage ratio (B), rotor solidity (σ) and tip speed ratio (λ). Comprehensive performance maps are generated to quantify the turbine's power coefficient (C_P) and hydraulic efficiency (η_Hy). A salient finding of this study is the evident divergence between the optimal values for maximum power extraction and maximum hydraulic efficiency. The maximum power configuration (C_P,max=4.23) is achieved at a high blockage and high solidity, yielding 3.95 kW. However, this aggressive loading induces a severe head loss of 6.97 m, resulting in low hydraulic efficiency (34.88%). In contrast, the maximum efficiency configuration (η_Hy,max=54.94 %) occurs at a moderate blockage and lower solidity, producing 1.86 kW but with a minimal head loss of 2.39 m. A fluid dynamic analysis of these two optima reveals that the C_P,max case is dominated by high loading, strong wake turbulence and significant tip-gap losses, while the η_Hy,max case operates with more stable flow structures and a larger cavitation margin. This research concludes that there is no single optimal design, but rather a fundamental trade-off between power output and hydraulic impact, contingent on the specific energy demands and pressure constraints of the installation site.