Motion Similarity of an Underwater Glider Based on Scaled Model

The similarity between two movements is the premise of predicting prototype movement characteristics and gliding economy using the scaled model of an underwater glider(UG). Taking the Petrel Ⅱ UG developed by Tianjin University as the research object, and starting from the similarity theory, the kinematic similarity criterion that the prototype and model of the UG should meet are deduced based on the dynamics and Navier-Stokes(N-S) equations. The computational fluid dynamics method is used to calculate the hydrodynamic coefficients of the UG at different scales, and the relationship between the scale similarity ratio and the lift as well as drag coefficients is obtained. Theoretical analysis shows that the Froude criterion is a necessary condition for the motion similarity of the UG prototype and its scaled model. In a certain scale range, the scale effect of lift coefficient and drag coefficient is not obvious, and it is most suitable to design the scale model with 0.5 as the scale similarity ratio. The Petrel Ⅱ UG scale model of the selected scale is tested in the pool, and motion parameters such as the speed and lift-drag ratio of the model at a certain pitch angle are obtained. The experimental results show that the motion similarity between the scaled model and its prototype is observed to exist. Results of the transverse velocity, vertical velocity and lift-drag ratio obtained from the scaled model in the tank tests are in good agreement with those of its prototype, obtained from the sea trials, and their relative errors meet the engineering error requirements. It is feasible to forecast the prototype motion parameters and gliding economy using the scaled model. The scaled model also provides a laboratory verification platform for the design of large UGs, which is of great significance to shorten the development cycle. © 2023 Tianjin University. All rights reserved.