Investigation Of The Mechanism Of Tail Slapping And Dynamic Modeling Of Supercavitating Vehicles

Supercavitation technology can greatly reduce the resistance of underwater vehicles,and increase the speed of navigation from 50 knots to more than 200 knots,significantly improving the penetration capability and destructive power of underwater weapons,which has become a hot research topic among military powers.At present,Russia has been equipped with "Storm" supercavitating straight-navigation torpedo,but due to its short range and poor maneuverability,its application scope and advantages have been seriously restricted.In order to improve the maneuverability of supercavitating weapons,it is urgent to study the principle of supercavitating maneuvering,master the hydrodynamic characteristics of supercavitating vehicle in the course of maneuvering,establish the dynamic model,and lay the foundation for the performance analysis and control system design.The topic of this paper comes from a pre-research project.The tail-slap characteristics of a supercavitating vehicle during turning maneuver under the action of the rudder angle of a disk cavitator were studied.Firstly,the flow field,hydrodynamic and trajectory characteristics under the influence of parameters such as cavitating flow pattern were obtained by numerical simulaiton.The formation mechanism of tail-slap motion was revealed.Then,a dynamic model for tail-slap motion was established.Finally,the accuracy of the model was validated by experiments.The main work and innovations are summarized as follows:(1)A coupling simulation model of flow field and trajectory for the tail-slap motion of a supercavitating vehicle was established.Using rigid body dynamics theory,a three-degree-of-freedom(3DOF)motion model of the vehicle was constructed.An unsteady numerical simulation model coupled with dynamic mesh technology was established to solve the flow field and the motion simultaneously.The numerical methods,meshing and solution models in the simulation model were verified and the simulation model was validated with the experimental results.(2)Based on the coupled simulation model,the tail-slap characteristics,flow field evolution and hydrodynamic and dynamic trajectory parameters of the vehicle during turning maneuver were studied in detail.The variations of the parameters in unsteady motion were described quantitatively,and the formation mechanism of tail-slap motion was revealed.The characteristics of tail hydrodynamics caused by the delay effect of cavity were different from those in steady motion.The unbalanced force characteristics of the vehicle resulted in the tail-slap motion.(3)The effects of cavitation number and rudder angle on the tail-slap characteristics were systematically analyzed.The variations of flow field,hydrodynamic and trajectory characteristics were obtained.The applicable range of cavitation number and rudder angle of the cavitator were indicated.The effects of speed on the tail-slap characteristics under the same cavitation number were studied.The conclusion was that the frequency of the tail slapping is proportional to the speed value,and the hydrodynamic coefficients and the trajectory parameters were consistent when the vehicle moves to the same position.The influences of a series of weighing parameters on the tail-slap characteristics of a vehicle were studied,and the mechanism of the effect of weighing parameters on the tail-slap characteristics was revealed based on the dynamics of rigid body.(4)A dynamic model of supercavitating vehicle including the delay effect of cavity was established,and a method for calculating the hydrodynamic of the tail using the equivalent angle of attack of the tail during the tail-slap motion was proposed.The position force characteristics of the tail were studied by simulation.The hydrodynamic of the tail calculated by the equivalent angle of attack was in good agreement with the coupling simulation,and the accuracy of the dynamic model was verified.An engineering algorithm model was constructed for the study of the tail-slap motion.(5)In view of the fact that most of the domestic and international experiments can only indirectly obtain a small amount of motion parameters of the vehicle through video recording,an experimental platform for the tail-slap motion of a supercavitating vehicle was built.An experiment model with inertial measurement unit and pressure measurement system was designed,and a series of experiments were carried out on an unpowered vehicle under different rudder angles.Accurate motion parameters and cavitation parameters of the vehicle were obtained.The simulation results were in good agreement with the experimental results,which verified the accuracy of the coupled simulation model and the theoretical research.