Investigation Into The Behaviors Of Ventilated Supercavitation Instability Under The Control Rudders

With the in-depth development of supercavitating vehicle technology,the straight line navigation can not meet the real application.The control of the posture and trajectory of the supercavitating vehicle is achieved by the controlling forces produced by the cavitator and tail fins.Actually,there are some negative effects produced during the movement of the rudders,such as the change of the internal pressure and flow field structure of the cavity,the deformation of the cavity boundary,increase of the gas leakage and instability of the cavity.Therefore,it is necessary to investigate the influences of rudder motion on the cavity.The influence factors and inherent mechanisms of unsteady cavitation induced by rudder were analyzed by theoretical method.The influence of movement frequency and angular amplitude of the rudders on the stability of ventilated supercavity was investigated under different rudder movement conditions,i.e.,cavitator motion without rear body,cavitator motion with rear body and tail supercavitation fins motion with rear body.The results shows that the change of supercavity geometry lags the change of internal pressure of the supercavity.The rudder movement will cause the slightly perturbation of internal pressure of the supercavity which is the main reason for the change of tail cavity closure regime and instability of the supercavity.Moreover,it forms the disturbing flow and vortex core at the zone near the cavity boundary,which will develop and strengthen with the continuous flow motion and lead to collapse of the supercavity.In addition,the flow field structure is more complex and the disturbance effects is enhanced which are caused by the interaction between rear body wall and injeting noncondensing gas.More specifically,the change trends of supeercavity diameter,length,axis offset and internal pressure were quantitatively analyzed under the action of the rudder moverment.With the increase of the angle,the supercavity diameter is reduced,the supercavity length and the internal pressure are increase.And,the large angular amplitude corresponds to large various of axis offset and internal pressure of the supercavity.The movement frequency of the rudder plays a key role in cavity unstable process.In all,the supercavity stability can be effectively improved by seting up the motion parameters of the rudders.The model with the movement rudders is designed and dynamic unstable cavitation flow experiments induced by controling rudder in a water tunnel is performed in this paper.The behaviors of the supercavity under dynamic movement conditions of the rudder were investigated.High-speed cameras and pressure sensors were used to collect the supercavity geometry and internal pressure.The results shows that the intensive re-entrant jet only forms located the rear cavity with white cloud cavity at the beginning,and the cloud cavity gradually develops to upstream of the supercavity as the frequency increased.The tail supercavity fins will produce local cavitation and couples with body cavity to increase the gas leakage.The gas barrier effects become strengthened when the rudder angle is growth,so that re-entrant jet prevents the formation of cavity.The experimental results of cavity axis and the variation of internal pressure under the rudder motion are good agreement with the theoretical and numerical.