Study On Mechanism Of Flow Noise From Under Water Open Cavity

Flow noise is the main noise source of underwater vehicle at high speed. Thus, it is very important to study how to effectively reduce the flow noise for sound stealth of underwater vehicle. Underwater open cavity, which can induce great fluid noise, becomes an important issue to reduce the underwater vehicle vibration and noise. This paper focuses on the characteristics of flow noise by underwater vehicle launch compartment and sails. The Large Eddy Simulation method combined with Lighthill's acoustic analogy theory, finite element method and infinite element is used by software FLUENT and ACTRAN to simulate the underwater flow noise.The launch compartment models are built up in two cases, case1: the cabin has no opening, case 2: the launch compartment has two different numbers of openings parallel to the flow direction. The flow noise frequency characteristics and its far field pattern are calculated and analyzed for different flow speed. The cloud pictures of surface pressure, velocity and eddy viscosity and fluctuating pressure diagram from various opening models are obtained and analyzed by numerical simulation; vibration and sound radiation spectral characteristics in underwater vehicle stations, near the bow vehicle and in the launch compartment are also calculated and analyzed; the effect of flow speed and attack angle on underwater vehicle launch compartment and acoustic radiation is discussed.We established three underwater vehicle sail models, model 1: without opening, model 2:with a opening vertical flow direction, model 3: with a opening and anechoic coating material on outside surface. The flow noise frequency characteristics and its far field pattern are calculated and analyzed for these models by numerical simulation for three different inflow speed; The effect of the opening and anechoic coating material on underwater vehicle sail flow noise is also analyzed. then, the experimental sail model with the same size as that in numerical simulation is designed and fabricated, and its flow noise is measured by reverberation chamber method in gravitational water tunnel of underwater acoustic technology laboratory. The experimental results show the correctness of numerical simulation calculations.