| The principle of supercavitation technology is to form a cavity to cover all or most of the surface of underwater vehicle,which can greatly reduce the frictional resistance of the vehicle,and significantly improve the speed of the underwater vehicle.Its investigation has attracted great attention from a large number of scholars.Since the mid-20 th century,great progress has been made in the research of supercavity technology.However,some scientific problems still need to be further studied on the multiphase flow characteristics of supercavitating vehicle under unsteady motion.These problems include: the influence of the wetted area of the vehicle on the structure of the wake and hydrodynamic characteristics of the vehicle;the influence of periodic flow on the multiphase flow of supercavity;the motion consistency between cavity and vehicle in turning motion and so on.All of them are the key scientific problems to be solved urgently in the field of unsteady flow of ventilated supercavity.Therefore,the multiphase flow characteristics of ventilated supercavity during typical unsteady motion are studied systematically in this paper.The main research contents and achievements are as follows:A three-dimensional computational model of unsteady ventilated supercavitating flow was established by using VOF multiphase flow model and RNG k-? turbulence model.By solving the Reynolds averaged Navier-Stokes equations for multiphase mixtures,the distribution of three-phase media in ventilated supercavitating flows was obtained,and the influence of watershed scale on the calculation results was analyzed.The effectiveness of the numerical simulation method was verified by comparing with the experimental data.Based on the computational model of unsteady ventilated supercavitating flow,the unsteady evolution process of multiphase wake structure of ventilated supercavitating vehicle was studied.The influence of gravity and the wetted area of the vehicle(aft body)on the structure of cavity wake was analyzed.By analyzing the pressure distribution in the flow field of the cavity wake and the vorticity distribution characteristics,the flow mechanism of the double-vortex tube wake structure and the triple-vortex tube wake structure were respectively clarified,and the change rule of the gas mass flow ratio,the vorticity and the pressure in the vortex tube at the cavity wake were given.Based on the unsteady ventilated supercavity method combined with the dynamic grid technique,a numerical model of periodic flow was established and verified.The flow field structure under periodic flow condition was obtained by numerical simulation,and the distribution law of wavelength and amplitude in a given basin downstream of wave flow field was analyzed.The unsteady multiphase flow characteristics of ventilated supercavity under periodic flow were studied.It was found that the motion state of supercavity was more stable in long wave environment.The closed mode of supercavity tail presented alternate changes of re-jet and double vortex tube under periodic flow.The change rule of cavitaty morphology and hydrodynamics of the vehicle under periodic flow was studied.A calculation model for the turning motion of a ventilated supercavitating vehicle was established.The numerical simulation result was compared with the calculated result based on the Logvinovich independent expansion principle,and the validity of the calculation model and the dynamic grid technique were verified.Based on the calculation model for turning motion,the influence of the turning center position of the vehicle on the wetted area and the influence of the turning radius on the ventilated supercavity shape and the hydrodynamic characteristics of the vehicle were analyzed.By using the control effect of cavitator on the axis of cavity,the method for keeping the motion consistency between cavity and vehicle in turning motion was proposed,which laid a theoretical foundation for the efficient maneuvering motion of supercavitating vehicle. |
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