Research on hydrodynamic performance of 2D undulating fin in the wake of a semi-cylinder.

The undulating propulsion of the dorsal fin of the black devil anglerfish underwater holds significant potential in robotics. However, the undulating propulsion mechanism differs from traditional fish swimming methods, especially regarding the motion principles under varying flow conditions, which require further investigation. Therefore, this study extensively explores the impact of cylindrical wake on the hydrodynamics of undulating fins by employing a two-dimensional numerical model. By defining the ratio γ of the distance between the cylinder and fin surface to the cylinder diameter, the study analyzes the hydrodynamic performance of the two-dimensional undulating fins at different Strouhal numbers. The research investigates dimensionless numbers such as average and transient thrust coefficients, power coefficients, efficiency, etc., to comprehensively understand the operational principles of undulating fins in time-varying flow fields. The results indicate that when γ =1, variations in the Reynolds number have minimal impact on the fin's hydrodynamic performance while increasing the Strouhal number can significantly alter the fin's hydrodynamic performance. Higher Strouhal numbers inhibit the formation of cylinder Karman vortex streets (KVS), but reducing efficiency. These findings lay a solid foundation for elucidating the passive hydrodynamic mechanism of fins utilizing cylindrical wake. • This study investigates the influence of cylinder wake on a fin's hydrodynamics. • This study investigates the effects of distance and cylinder diameter on fins. • This study investigates the impact of Re and St on the fin's hydrodynamics. [ABSTRACT FROM AUTHOR]