Research Of Hydrodynamic Noise On3D Rigid Cavity-Cylindrical Convex Body Composite Structure

Cavity, convex body and their composite structure are common structures onthe surface of autonomous underwater vehicle (AUV). During water flowing overthese structures, hydrodynamic noise can then be induced. The hydrodynamic noisewill not only influence the measuring accuracy of the acoustic instruments mountedon the AUV, lower the acoustic concealment performance, but also bring noisepollution to the marine environment and influence the normal growth of marineorganism. There have been many researches about cavity and cylinder’saerodynamic noise, but there are few researches about hydrodynamic noise of cavity—convex body composite structures. Furthermore, hydrodynamic noise has its owncharacteristics different from aerodynamic noise. In a word, it is necessary toconduct researches of hydrodynamic noise on cavity-convex body.Based on the structure characteristics of antenna and acoustic communicationmounted on the AUV, cavity-cylinder composite structure is abstracted. The largeeddy simulation (LES)-Lighthill equivalent source method is used to investigate theunsteady flow mechanism and hydrodynamic noise of the structure. The presentstudies will provide theoretical guidance for reducing noise of AUVs. The obtainedachievements are as follows:(1) The unsteady flow mechanism and hydrodynamic noise of cavity-cylindercomposited structure, cylinder, and cylindrical cavity are analyzed. It shows that forcavity-cylinder composited structure, the boundary layer flow of cavity is weakened,because of the cylinder’s existence. The acoustic radiation neither shows dipolecharacteristics like the cavity, nor shows quadripole characteristics like the cylinder.(2) Based on the orthogonal test, the influence of four factors on thehydrodynamic noise of cavity-cylinder composited structure is analyzed. It showsthat when the velocity of AUV is low, the influence of velocity on thehydrodynamic noise is not significant. The ratio of height and depth is the mainfactor. The ratio of diameter is the secondary factor. Rectangular cavity-cylindercomposite structure has lower hydrodynamic noise than the cylindrical cavity-cylinder composite structure does. (3) The unsteady flow mechanism and hydrodynamic noise is researched, whenthere is a cylinder in the upstream of the cavity-cylinder composite structure. Itshows that when the center distance is shorter than (or equal to)3d (d is the diameterof the cylinder), the cylinder in the upstream has much influence on thehydrodynamic noise of the cavity-cylinder composite structure in the downstream.When the center distance increases to4d or larger, the interaction between thecylinder and the cavity-cylinder composite structure is weakened, and their flow andacoustic radiation are independent with each other.