Research On Multiphase Hydrodynamic And Attitude Of Submarine Launched Vehicle With Boundary Layer Ventilation

The major characteristics of cavititing flow with submarine-launched process is transient,unsteady and nonlinear.In addition,the cavity development is easily affected by wave and sea route,which make it have complex flow structures.This cavititing flow has great significance in the hydrodynamics design of underwater vehicle.The hydrodynamics characteristics can be controlled by ventilation technology,which can improve the lauching success rate.A serial multi-phases fluid experiments,numerical simulations and theoreticle studies are carried out on underwater vehicle with streamline head and boundary layer ventilation technique,and the mechanism of flow structures during the cavity generating and developing is revealed.Otherwise,the body atittude characteristics introduced by ventilating cavity hydrodynamics are discussed in this thesis.Combined experimental and numerical simulations are applied to study boundary layer cavititing flow based on flat plate model in a water tunnel.the transient process of cavity generation,evolution are obtained,and the induced phase and pressure distribution are analyzed.Based on the calculated and experimental results,vortex structure sketch of gas jet in water crossflow were studied thoroughly.The development of counter rotating vortex in the upwind direction intercept the water stream attached on the plate,meanwhile enhance adjacent cavity expanding in cross direction and formating a film cavity covering the flat plate.The influences of Eu,Fr,gas flow rate,the holes distribution modes and pitch of holes are disccussed.It reveals that the smaller Fr,smaller pitch of holes,larger gas flow rate and in-line holes arragement will enhance the cavity interation in cross direction and improve the steability of cavity film.On the basis of the mechanism of boundary layer ventilating cavity generation and evolution,a mathematical model based on RANS equation and interfacecapturing method is developed.A dynamic mesh technology with local domain restruction and flow fuild infamation interpolation technique are proposed to achieve the three-dimensional motion of the underwater object and couple the rigid body motion with the cavity flow hydrodynamic.The numerical results of multiphase phenomena,the law of cavity parameters change and the object surface pressure distribution agree well with the experimental results,the mathematical model and simulation method are thus verified.The unsteady developing process of boundary layer ventilating cavity with different ventilation modes are investigated to find out the adjacent cavity connection machnism and the interaction between cavity hydrodynamic and underwater vehicle attitude.The ventilating cavity fluid structure can be devided into gas domain,mixed phase domain and trailing region depanding on the phase components.The re-entrant jet will carry liquid into cavity,mixing with gas phase,which generate the three dimentional vortex motion in mix phase domain and enlarge the cavity film region.Due to the equal pressure effect resulted by formation of boudary layer cavity film and its moving orientating the vehicle tail,the fluid flow structures and hydrodynamic characteristics on vehicle surface are changed significantly.Considering the influence of launch vehicle and cavity asymmetry development induced by pitch acceleration,the pitching moment applied on vehicle surface make the atittude better during water exit process.As a consequence,boundary layer ventilating cavity is able to adjust the fluid hydrodynamic acting on vehicle surface and the vehicle movement attitude.