Numerical investigation on noise reduction mechanism of serrated trailing edge installed on a pump jet duct

For ships, the stealth performance is an important indicator of its vitality. It is extremely important to study the noise reduction of ship propulsions. In this work, pump-jet propulsion with a DARPA Suboff submarine was taken as the investigated object. The trailing edge of its duct was transformed with some serrations, and its noise reduction effect was studied. Large Eddy Simulation (LES) method was utilized to predict the hydrodynamic performance of the pump-jet propulsion. Then the FW-H acoustic model was added into the noise performance simulation after the flow stabilization. After the installation of the serrated trailing edge, the propulsion Sound Pressure Level (SPL) changes were observed. According to the contributions of different parts to the noise intensity and the vortex field changes, the noise reduction effect was analyzed. The results indicate that not only the propulsion noise radiation but also the noise reduction effect is directional. Due to the larger noise contribution of the duct, the serrated trailing edge has a better effect in the radial direction. In addition,the circumferential correlation of the duct vortex is broken by the serrations, the large vortices are divided into several small ones, and the vortex diffusion is accelerated.