Performance Improvement of Hydrofoil with Biological Characteristics: Tail Fin of a Whale

In order to improve the hydrodynamic performance of hydrofoils, this paper shows excellent hydrodynamic performance according to the flapping motion of fish through the tail fin. The Naca66 hydrofoil is used as the original hydrofoil and the trailing edge flap configuration is added. Ansys-fluent is used to analyze the relationship between the structural parameters (length and angle) of the flap and the hydrodynamic performance of the hydrofoil, the reliability of CFD numerical simulation is verified by PIV experiment. It is found that the hydrofoil, with clockwise rotating short flap, can significantly improve the hydrodynamic performance of a hydrofoil at a small angle of attack; at a high angle of attack, the hydrofoil with counterclockwise flap can increase the critical stall angle and slightly improve the hydrodynamic performance of the hydrofoil. The hydrodynamic performance of hydrofoil with rotatable short flaps reported in this paper can provide valuable information for the design and optimization of this kind of hydrofoil.

Numerical Simulation of Flow over Bionic Airfoil

In this study, the aerodynamic performance of bionic airfoil was numerically studied by CFD method. The bionic airfoil was represented by the combination of airfoil and a small trailing edge flap. A variety of configurations were calculated to study the effect of flap parameters, such as the flap angle, position, and shape, on the bionic airfoil aerodynamic characteristics based on two layouts which were that (1) there was a tiny gap between the airfoil and the flap and (2) there was no gap between the two. The results showed that the flap angle and position had significant effects on the aerodynamic performance of the airfoil with the two layouts. Compared with the clean airfoil, the maximum lift coefficients of the first layout and the second layout could be increased by 10.9% and 7.9%, respectively. And the effective angle of attack (AoA) range for improving the lift-to-drag ratio could reach 7°. The flap shape also affected the airfoil aerodynamic characteristics, and the flap with the sinusoid curve shape showed ideal performance.

Modeling and Control of Dynamic Stall Loads on a Smart Airfoil at Low Reynolds Number

This article describes the development and testing of a modified, semi-empirical ONERA dynamic stall model for an airfoil with a trailing edge flap—a “smart airfoil”—pitching at reduced frequencies up to 0.1. The Reynolds number is 105. The model reconstructs the load fluctuations associated with the shedding of multiple dynamic stall vortices (DSVs) in a time-marching solution, which makes it suitable for real-time control of a trailing edge flap (TEF). No other model captures the effect of the DSVs on the aerodynamic loads on smart airfoils. The model was refined and tuned for force measurements on a smart NACA 643-618 airfoil model that was pitching with an inactive TEF and was validated against the measurements when the TEF was activated. A substantial laminar separation bubble can develop on this airfoil, which is challenging for modelers of the unsteady response. A closed-loop controller was designed offline in SIMULINK, and the output of the controller was applied to the TEF in a wind tunnel. The results indicated that the model has a comparable accuracy for predicting loads with the active TEF compared to inactive TEF loads. In the fully separated flow regime, the controller performed worse when dealing with the development of the laminar separation bubble and DSVs.