Study On Flow Characteristics Of Ventilated Cavitation Around The Submarine Launched Vehicle

Active ventilation is a kind of effective means of underwater flow control. Bubble gas into water through the vehicle surface blowhole, seam, in order to form air bubbles, air layer, gas cavity multiphase flow structure, can effectively induce drag reduction, load and improve the flow stability. As the changes of factors such as the ventilation volume, sailing speed, head type, it will have different flow patterns, and there are significant differences in sensitivity to environmental conditions and hydrodynamic pressure characteristics. In this thesis, use the numerical simulation method, axisymmetric bodies as the research object, to research the different ventilation structures and flow parameters effect of multiphase flow field around the bodies. The main work in this thesis is shown as follows:The application of multiphase flow models and turbulent models are evaluated in the numerical calculation of underwater launch bodies ventilation cavitation. The multiphase flow models has a great influence on of cavitation morphology. Compared to the Mixture model, Level set model calculation results cavity form is close to the experimental condition. Turbulent model has a great influence on the cavitation fracture. Compared with the standard k-ε model, RNG k-ε model can simulate the fracture and tail off of the cavitation. Based on the comparison of experimental results, this thesis select Level set model and the RNG k-ε model for numerical calculation.The influence of different kind of exhaust ventilation structures on ventilation cavity flow characteristics is demonstrated. Fork exhaust ventilation structure make the inner cavity mixed more evenly, can reduce the vehicel body surface pressure, but there is a big relatively high pressure in the rear part of cavity, and form the re-entrant flow. In-line ventilation structure can delay the time of cavitation broke off, reduce the bodies pressure fluctuations around axial and circumferential. Under the influence of lateral flow, in-line ventilation structure can reduce the pressure of bodies to positive side and back surface.The influence of the ring groove structure on ventilation cavity formation and circumferential pressure fluctuations is demonstrated. Ring groove structure make the gas mix well inside the ring groove, then flow out the ring groove is formed uniform cavity, can significantly reduce the circumferential pressure fluctuations. The ring groove is wider, gas inside the ring groove will mix more fully, the cavitation is more uniform, can reduce the circumferential pressure fluctuations. Under the influence of lateral flow, the ring groove structure make the cavitation cover the body surface better.The influence of ventilation rate on ventilation cavity flow characteristics is analyzed. With the increase of ventilation rate, cavitation is mixed more evenly and thickness increases gradually, the effect of reduce the vehicle surface pressure increases. But the increase of ventilation rate lead to relatively high pressure increasing, forming re-entrant flow, and then make the cavity length develop slow, causing cavitation broke off. Increase of ventilation rate within a certain range can reduce the circumferential pressure fluctuations, but continue to increase, the circumferential pressure fluctuations will be increased.The influence of acceleration and deceleration on ventilation cavity circumferential development is analyzed. When the vehicle launched underwater, deceleration motion makes caviton development speed slow, bubbles are beneficial to circumferential development, when bubbles in a shorter distance to form ventilation cavity formation, is helpful to reduce the surface circumferential pressure fluctuations.