Research on the propulsion performance of spring-hydrofoil mechanism of the wave glider

Abstract

It is essential for a wave glider to get larger propulsion by improving the efficiency of flapping hydrofoils to harvest wave energy. In this paper, the propulsion performances of spring-hydrofoil mechanism (SHM) of the submerged glider of the wave glider were investigated by changing spring stiffness coefficients (SSC) and limited pitching angles (LPA) under the same wave amplitudes and frequencies. The overset mesh technology of the computational fluid dynamics (CFD) software FLUENT was used to build a grid model for a two-dimensional hydrofoil, and the mathematical equations of the SHM were modeled and embedded in the user-defined functions (UDF) for simulation. The simulation results showed that the propulsion efficiency gradually decreased with the increase of the SSC, while the average propulsion of the hydrofoil fist increased and then decreased, which reached a maximum value whenK=5000N/m. And the propulsion efficiency of the hydrofoil continued to increase as the LPA gradually increased, and the average propulsion of the hydrofoil reached a maximum value whenβ=25°. It was found that the forward thrust of the hydrofoil could be improved by the LPA and the instability under larger wave heights could be avoided. The sea trials were carried out and the results showed that the average velocity of the “Black Pearl” wave glider withβ=25°was 0.372 m/s, which was 30% more than that of the wave glider without β under the same sea state.