From Ancient Aqueducts to Modern Turbines: Exploring the Impact of Nazca-Inspired Spiral Geometry on Gravitational Vortex Turbine Efficiency

This study investigates an inlet design for a gravitational vortex turbine (GVT), drawing inspiration from the ancient Nazca puquios. The puquios are ingenious subterranean aqueducts constructed by the Nazca culture (c. 100 BC–800 AD) in southern Peru, featuring spiral ojos de agua (water eyes) used to access groundwater and stabilize flow.The primary objective was to enhance vortex stability and overall GVT efficiency under low-head, low-flow operating conditions. A parametric Nazca-type inlet feeding a conical basin was defined by two controlling factors: the number of turns (N) and the inclination angle ($\theta$). The optimal geometry was determined through a $3^2$ full factorial design, computational fluid dynamics (CFD) simulations, and response surface methodology (RSM), with vortex circulation $\left(\Gamma \right)$ serving as the optimization metric. The best-performing inlet configuration ($N=4$, $\theta ={13}^{\circ }$) yielded $\Gamma =1.3459$ m²/s. This circulation level is comparable to that reported for optimized conventional wrap-around inlets at similar flow rates, but uniquely produced a broader and more symmetric vortex structure. Subsequently, two four-bladed runners (one with twisted blades and one with curved cross-flow blades) were evaluated numerically and experimentally using a laboratory-scale prototype operated at a consistent flow rate ($Q\approx 0.00143$ m³/s). CFD predicted maximum efficiencies of $15.37\%$ and $17.07\%$ for the twisted and curved runners, respectively, while experimental tests achieved $8.70\%$ and $11.61\%$, demonstrating similar efficiency($\eta$) versus angular velocity ($\omega )$) characteristics. These results indicate reduced hydraulic effectiveness of the Nazca-inspired geometry for the GVT, with experimental efficiencies below those reported in the literature.