NUMERICAL STUDY ON CAVITATING FLOW NOISE CHARACTERISTICS OF UNDERWATER AXISYMMETRIC BODY UPON POROUS FW-H METHOD

The cavitating flow noise has an important influence on the stealth performance and maneuvering stability of an underwater axisymmetric body. The large eddy simulation combined with porous FW-H method is used to simulate the noise characteristics of cavitating flows around two axisymmetric bodies with a blunt head and a conical head of 90°. The noise spectrum characteristics and sound field directivity for these two bodies are analyzed under the conditions of non-cavitation and a cavitation number of 0.8, respectively. The numerical method reliability is verified upon the experimental results. The research shows that the time-evolution process of cavities has a close relationship with the noise characteristics. There is a high negative correlation between the vapor volume and sound pressure. The immense pulse of sound pressure is found during the break-off and the collapse process of local cavities. At the gathering and merging stage, the sound pressure can gradually decrease. The noise peak frequency agrees well with the cavity shedding frequency. In the direction perpendicular to the incoming flow, an obvious broadband peak occurs in the high frequency band due to the cavities around the bodies. In addition, the sound field directivity respectively presents the dipole characteristic for non-cavitation and monopole characteristic for cavitation. By contrast, the cavity scale around the blunt-headform axisymmetric body is larger and its variation acceleration is larger too, and the instantaneous noise is stronger. Compared with that of the cone-headform body, the average total sound pressure level at far sound field of the blunt-headfrom body is 8.7 dB higher.