A CFD application in optimizing the drag force acting on a bionic undulating fin

Abstract

Nowadays, autonomous underwater robots are being widely applied around the world to replace humans in surveying the rivers and lakes; researching the oceanography; spying in narrow spaces - places that are hard for humans to reach. When robot moves underwater, there are many factors that affect the robot's movement, especially hydrodynamic resistance. This reduction in drag helps to reduce the power of the motor, save costs in design and manufacture. This paper studies the drag force acting on two undulating fins with different profiles by the computational fluid dynamics (CFD) method with the popular turbulence model k-ε, the Navier-Stokes equation, and the hydrodynamic drag equation. The results show that the shape of the fin has a significant influence on the drag, especially when the fin profile design has a decreasing amplitude with length, the drag tends to decrease. At the swimming speed of 0.2m/s, the drag force on the improved model is reduced to 0.07N, compared to the traditional model of 0.95N. In addition, the influence of swimming speed is also investigated in this paper. When the swimming speed increases from 0.1m/s to 0.3m/s, the drag force on the improved model increases from 0.02N to 0.16N while that in the traditional model increases from 0.26N to 2N. The model was built by Spaceclaim software and simulated to calculate and optimize drag by ANSYS Fluent with boundary conditions and parameters consistent with previous experiments.