The Optimal Lift–Drag Ratio of Underwater Glider for Improving Sailing Efficiency

Abstract

It is generally believed that the lift–drag ratio is closely related to the hydrodynamic performance and sailing efficiency of the underwater glider. The underwater glider carries limited energy, making it particularly important to increase the sailing efficiency through selection of an appropriate lift–drag ratio. Considering this, the energy consumption per meter is introduced as the indicator of sailing efficiency and the energy consumption models under given net buoyancy and glide speed are established, respectively. Then, the optimal lift–drag ratio for sailing efficiency is obtained through these two models. The result shows that under given net buoyancy, the sailing efficiency has positive correlation with the lift–drag ratio. The optimal lift–drag ratio at this time is the maximum lift–drag ratio that can be obtained at a speed above the minimum allowable, and the glider shapes with a high ultimate lift–drag ratio, such as the flying wing layout or high aspect ratio wings, can be adopted. However, under a given speed, it is not the higher the better for the lift–drag ratio, but the optimal lift–drag ratio is a constant value only related to the shape of the glider to maximize the sailing efficiency. What's more, the glider shapes with a low ultimate lift–drag ratio, such as low aspect ratio wings, can decrease the lower limit of minimum energy consumption per meter and also can be adopted under a given speed.