Research On The Interaction Mechanism And Flow Control Methods For Ventilated Cavity With Exhausted Gasous Jet

Supercavity is acknowledged as a promising technology in ultrahigh speed,crossmedium projectiles due to its high drag reduction efficiency.For underwater supercavity vehicles powered by jet propulsion,the disturbance of the tail jet may cause the deformation,oscillation and collapse of the cavity interface,which brings new challenges to the accurate prediction and stability control of the cavity shape.In this paper,a combination of numerical simulation,experimental study and theoretical analysis is used to conduct research on the mechanism of cavity-jet coupling and flow control methods.Relatively perfect prediction model is established to reveal typical cavity instability mechanism,and a flow control method of multi-cavitator is proposed to realize engine gas drainage and cavity stabilization.Based on the classical cavity theory and jet theory,the theoretical analysis of the coupling effect of ventilation cavity and jet is carried out.A discriminant formula is derived from mass and momentum conservation of the gas flowing inside the cavity under ideal conditions,and the important dimensionless parameters are deduced.Based on the gravity water tunnel,an experimental system for the coupling interaction of ventilation cavity and supersonic jet is constructed.A compressible multiphase flow simulation model is constructed by combining the interface tracking method,turbulence model,and phase transition model,then examples of cavity-jet coupling are given to verify the accuracy of the simulation model.Based on water tunnel experiments and numerical simulations,the evolution law of the cavity interface under the action of normal temperature jet is studied.By changing ventilation flow rate,jet flow rate and model legnth,three distinct mechanisms are observed and divided into the flowing types: inflated cavity model(ICM);partially deflation model(PDM);strong deflation model(SDM).The calculation model of the cavity size and critical transition conditions for differernt mechanism are further built;The model conversion map associated with the key parameters(dimensionless momentum ratio and the relative position)is constructed on the current experiment and simulation datas;Further,the drainage effect analysis are carried out through time sequence control,and the formation and stability conditions of the drainage supercavity are also obtained.Based on the solid gas generator and the water tunnel experimental system,the coupling mechanism of exhausted gasous jet and ventilation cavity is studied,and the influence of the diameter change on the cavity-jet coupling model and the drainage effect is analyzed.By comparing the experimental results of exhausted gasous jet and normal temperature jet,the influence of temperature gradient and phase change on the flow field structure is analyzed with the help of numerical calculation results.The three typical cavity instability mechanisms under the action of tail jet are further analyzed,which lays the foundation for flow control.From the perspective of combining active and passive flow control methods,the influence mechanism of projectile shape change and local inflation on the flow field structure and interface fluctuation inside the cavity is explored.The novel configuration of the underwater vehicle can achieve the dual purpose of enhancing the drainage effect and improving the cavity stability,and the expansion and contraction multi-cavitator model tests have been carried out respectively.Compared with the conventional model,the contraction multi-cavitator model can realize rapid air bleed with small ventilation rate,and maintain a relatively-stable double-cavity flow pattern at the ignition moment,which could reduce the fluctuation frequency and amplitude of the cavity interface to avoid the hydrodynamic instability caused by local large-area wetting of the projectile.