Characteristics And Test Methodology Of Flow Noise On Optical Hydrophone Towed Array

Flow noise is the dominate noise of the towed array sonar. It is also one of the technical difficulties in the development of optical fiber hydrophone thin line towed array. Under the background of the application of thin line towed array, this thesis investigated the optical fiber hydrophone thin line towed array technology and flow noise suppressing methodology. On the basis of the miniaturization of the hydrophone elements and the optimization of the thin line structure, a thin line towed array with a diameter of 20mm was trial-produced. One powerless towed-body flow noise measurement system was developed. Flow noise measurement of smooth PU cylinder was carried out consequently and very low flow noise level was obtained under the towed speed of 8 knots. For the purpose of further suppressing the flow noise, the thesis investigated bionic de-noise technology. On solving the art related problem through the examination of hydrodynamic on the bionic rib-lets surface, bionic membranes with turbulent boundary noise suppression ability were manufactured. Tests of the noise suppression characteristic of the bionic membranes were done through low noise powerless water tunnel and towing measurements were completed on the lake. The result showed the following conclusions. 1) The rib-lets membrane showed a de-noising effect of 4dB in the water tunnel test. 2) The rib-lets membrane has obvious flow noise suppression at high towed speed and high frequencies. 3) Its flow noise suppression ability fades when towed at low turbulivity. 4) Optical towed array, which has longer acoustic segment and oscillating damping segments or with well-designed towed tail, would probably have low flow noise level. 5) The powerless water tunnel is efficient for measurement of the flow boundary noise.