Study On The Cavitating Flows And Pressure Fluctuation For Underwater Vehicle

It is well known that the ventilated cavitating flow around an underwater vehicle is a complex,multi-scale,multiphase phenomenon.The unsteady process of cavitating flow contains growth,break-off,shedding and collapse of cavity.It involves compressibility,vortex motion and many other complex turbulent flow phenomena.The mechanism of the transient ventilated cavitating flow problems related to underwater weapons and aerospace.The fundamental research of ventilated cavitating flow is valuable in engineering,because it can help to understand the characteristic of cavitating flow.The ventilated cavitating flow is investigated by combined experimental and numerical analysis.In order to solve the problem of unsteady cavitating flow around an underwater vehicle,the unsteady cavity shape and the characteristics of pressure fluctuation under natural cavitation and ventilated cavitation are investigated.The main outlines are summarized as follows:A simultaneous sampling system for cavitating flow in water tunnel is established,it combines the high speed camera system,pressure measurement system and air injection system.Based on the simultaneous sampling system,the evolution of cavity shape can be synchronized with the pressure signals.Then,the cavity shape and pressure fluctuation at the same instant in unsteady cavitating flow can be captured to illustrate their correlation.In order to understand better the ventilated cavitating flow structure around an underwater ventilated vehicle,a high speed camera system is used to observe the cavity evolution of unsteady cavitating flow and a dynamic pressure measurement system is used to measure the instantaneous pressure during cavity growth.Based on the simultaneous sampling system,the cavity shape and pressure fluctuation of unsteady cavitating flow around an underwater vehicle are obtained.The growth,break-off,shedding and collapse of cavity evolution and the induced pressure fluctuation are obtained experimentally.The relationship between cavity evolution and pressure fluctuation is analyzed.The time and frequency domain characteristic of pressure fluctuation under different cavitation numbers are investigated.According to the distribution of pressure fluctuation,it's found that the vibration of the model is induced by the pressure fluctuation in the region covered by shedding cavity.The evolution of ventilated cavitation and the instantaneous pressure signals are observed after ventilation began and stop.The shedding cavity and pressure around the ventilated vehicle are investigated in water tunnel.The ventilated flow rate of the gas influences the development of ventilated cavitation,and the pressure fluctuation is suppressed remarkably by the ventilated cavity evolution.The characteristic of cavity collapse and the pressure fluctuations are obtained after ventilation stop.Based on the theory of homogeneous equilibrium flow model,the numerical model is established by secondary development of computational fluid dynamics code CFX with a filter-based turbulence model(FBM)for ventilated cavitating flow.Compared with experimental unsteady cavity evolution morphology,the proposed method can effectively capture the unsteady cavitating structure in accordance with the quantitative features observed in the experiment.The computed pressure fluctuations qualitatively follow the experimentally observed trend,and the good quantitative agreement is obtained.It is clear that the FBM can effectively capture the unsteady features.Based on the numerical method of unsteady cavitating flow,numerical simulation is conducted over three-dimensional ventilated vehicle.The flow structure and vortex motion of unsteady cavitating flow are analyzed.The evolution of ventilated cavity and pressure fluctuation are obtained.The relationship between cavity evolution and vortex structure in the cavitating flow field is analyzed.The mechanism of pressure fluctuation excited by ventilated cavitation development is illustrated.