A numerical simulation of flow-induced noise from cavity based on LES and Lighthill acoustic theory

摘要

The flow noise has become an important factor affecting the acoustical stealth performance of AUV in high speed. In the broad sense, all of the radiated noise caused by the instability of the flow field is called flow noise, including the fluid's own noise and noise radiation from flow-induced vibration. Both of the two subclasses of flow-induced noise are investigated in this paper and a precise and efficient numerical method is introduced. With the commercial computational fluid dynamics (CFD) software Fluent and acoustical finite-element method (FEM) software ACTRAN tuned to work jointly with types of preprocessing and post processing software, a computing mechanism combined with large eddy simulation, structural FEM and Lighthill acoustic analogy theory was established. A fluid-structure interaction handling method for shell elements with heavy fluid on both sides was also constructed, which achieves a remarkable reduction on manpower and computational cost on modeling and discrediting the shell structures. A prominent improvement in performance for a flow-induced noise solver on submerged complicated shell structures is also observed. For the validation of our method on both flow-stimulated radiation and flow-induced noise, a number of experiments were conducted on flow-stimulated thin shells and cavity flow-induced noise, consist with the general law of fluid-noise. The method was then applied to the flow-induced noise from a submerged wing-shaped cavity and nozzle, and the pattern of corresponding flow field and sound field further investigated. A corrected reverberation measuring method was also established to overcome the difficulty of flow-noise induced by the noise measurement. Once the spatial mean level of sound pressure in the reverberation control area is measured and corrected, the sound radiation power induced by a submerged complicated source can then be swiftly obtained. The computing method combined with large eddy simulation, structural FEM and Lighthill acoustic analogy theory is further validated by experiments on the flow-induced noise from a submerged wing-shaped cavity in the gravitational water tunnel of an underwater acoustic technique laboratory using our reverberation chamber measuring method. The experimental data fits the simulation solution well.