Optimal propulsion efficiency for NACA0012 foils with asymmetries in motion: A hybrid approach using the Taguchi method and artificial neural networks

This study uses the Taguchi method and artificial neural networks to optimize the thrust and propulsion efficiency of a NACA0012 foil, examining variables like downstroke duration (S = 0.3–0.5), angle of attack during downstroke and upstroke (αmd, αmu = 20°–50°), and Strouhal number (St = 0.2–0.5). Analysis shows that the St greatly affects thrust, while the αmu is pivotal for propulsion efficiency. Thrust is optimized by using a shorter S of 0.3, a greater αmd of 50° and a larger St of 0.45–0.5 and efficiency is optimized by using symmetric S of 0.5, a smaller αmd, αmu of 20° and a lower St of 0.35–0.39. Force and flow field analysis shows that certain combinations optimize thrust by mitigating negative thrust in the early downstroke, though they increase power consumption, lowering overall efficiency. Configurations balancing stroke duration and minimizing the angle of attack enhance efficiency by decreasing power demand for steady thrust. Wake structure analysis reveals that optimal efficiency involves generating reverse Kármán vortex streets, while optimizing thrust leads to a more chaotic wake. This study advances fluid dynamics in propulsion systems and aids in designing more efficient, adaptable underwater vehicles by identifying the key balance between thrust optimization and propulsion efficiency.