Hydrodynamic analysis of water-jet thrusters for the spherical underwater robot (SUR III)

For the propulsion system of an underwater robot, the nozzle of the water-jet thruster plays an important role in converting energy to generate the reaction thrust. In order to achieve a higher reaction thrust, hydrodynamic analysis of the water-jet thruster is introduced in this paper. First, the prototypes of the third-generation Spherical Underwater Robot (SUR-III) and the water-jet thruster are given. Then the design principle of conical nozzle is described in detail. The shape of nozzle is changed from the traditional cylindrical one to conical one. The control angle is used to change the reaction thrust of the water flow in the outlet of nozzle. Before making the hydrodynamic analysis, we use Solidworks2011 to establish 3D models of conical nozzles with different control angles. Some unimportant parts causing limitations are ignored to simplify the analysis. Finally, ANASYS CFX is employed to make the hydrodynamic analysis. Comparing the simulation results with theoretical values, the velocity error is less than 6.64%. The simulation results show that the increase of control angle of conical nozzles can increase the reaction thrust of water-jet thruster. Meanwhile, the reaction thrust of conical nozzle with 20° control angle is more than two times as big as that of cylindrical nozzle.