| The mutual interference widely exists between objects moving in close proximity in nature and daily life,such as migrating geese,fish and shrimp,fleets in narrow channels,and formations of high-speed aircraft,and strict rules have been made to ensure a sufficient safe distance and prevent the potential hazards from turbulent wakes.This interference also inevitably exists between the vehicles launched successively underwater and is more intense due to the higher density and viscosity of the water.As a comprehensive problem covering many basic research directions in the fluid field,the underwater launch has always been the focus of academia and engineering.However,the underwater motion process of vehicles not only involves complex flows,including wall shear flow around the vehicle and turbulent vortices formed by the flow transition and separation,but also usually accompanied by free shearing at the gas-liquid interface and interphase mixing and transformation caused by the cavities attached to vehicles.The strong instantaneous unsteady characteristics greatly increase the difficulty of studying the hydrodynamic characteristics of underwater launched vehicles.Nowadays,with increasing demand on successive launching capacity of submarines,it has become increasingly urgent to conduct researches on the mechanism and laws of interference between underwater successively launched vehicles,but current studies on this topic is still limited,and the relevant experiments and theoretical models are almost blank.In this regard,this paper qualitatively and quantitatively study the hydrodynamic and motion interference characteristics of underwater successively launched vehicles by using the numerical,experimental,and theoretical methods.The main contents and results are as follows:For the two-phase turbulent flow field formed by the successive launch,the physical models are compared and optimized to capture the main structural features of the flow field,and a numerical model of two vehicles with six-degrees of freedom is established based on the VOF model and 6)- model.After comparing with the experimental results and completing the validity verification,the numerical model is used to study the structure evolution of the underwater successive launch flow field and the hydrodynamic interference between two vehicles.Combined with the streamline convolution texture,vorticity,and Q-criteria isosurface in the flow field,the formation and evolution process of the hairpin vortex structure behind the vehicle with an angle of attack is clarified.Then,the pressure disparity between the windward side and leeward side of the second vehicle generated by the vortex structure is presented,together with the hydrodynamic and motion characteristics.Finally,the mechanism of the interference between two successively launched vehicles is revealed.Based on the underwater successive launch device with the controllable transport velocity and time interval and the experimental observation system that records the experimental multiphase flow field and the six-axis motion data of vehicles,the experimental research on the effects of the launch time interval,launch transport velocity,launch sequence,and nose shape of the vehicle on the hydrodynamic and motion characteristics of the successively launched vehicles is carried out.The hydrodynamic coefficients,trajectories,pitch attitudes of the vehicles,and the interference intensity represented by the attitude disparity between two vehicles under the above parameters are obtained quantitatively.Combined with the numerical flow field structure,the influence mechanism of the launch parameter on the interference between vehicles is revealed.The critical time interval corresponding to a negligible interference is obtained,and the early break and dissipation of the hairpin vortex caused by the reduction of the composition of the counter-rotating vortex tubes at a low transport velocity being contributed to the weaken of the interference effect on the second vehicle is pointed out.Moreover,it is found that the interference effect under the windward launch sequence is weaker than that under the leeward launch sequence.Additionally,the variation of the interference between the conical-nosed vehicles with the launch time interval and transport velocity is similar to that of the ellipsoidal-nosed vehicle,but the strength of the interference is reduced.Based on the potential flow theory and slicing method,a theoretical model on the hydrodynamic and underwater motion of the vehicle after detaching from the launch tube is established,and the distribution characteristics of the force components along the axis of the vehicle and their quantitative evolution during the underwater motion are presented.The hydrodynamic forces on the slice are determined by the parameter of the slice,local velocity,and angle of attack.The unit cross forces on the head is always larger than those on the cylindrical body during the underwater movement,while the total cross force and pitch moment of the vehicle decrease with the angle of attack.After completing the theoretical model of the single vehicle,the interference on the second vehicle is obtained by modeling the vortex flow and calculating its force on the second vehicle.In this way,the initial strength along the axis of the vortex tube and the hydrodynamic and motion characteristics of the second vehicle are presented.For the conical-nosed vehicle,the position of the non-wetting zone is determined by establishing an evolution model of the shoulder cavity,and the hydrodynamic model of the conical-nosed vehicle is established by using the parameters of the conical nose and the corresponding flow characteristics.Finally,it is confirmed that the conical head will be subjected to a larger cross force than the ellipsoidal head,and why the conical-nosed vehicle at high transport velocities would experience a larger pitch deflection in the absence of hydrodynamic forces in the non-wetting area wrapped by the shoulder cavity is interpreted. |
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