Serration of the duct trailing edge to affect the hydrodynamics and noise generation for a pump-jet propulsor

Inspired by the silent gliding feather of owl wings, the trailing edge of the duct of a pump-jet propulsor was designed with a similar serrated structure in order to reduce noise generation. Two distinct serrated structures were proposed and evaluated using the detached eddy simulation method with the shear stress transport k - omega turbulence model. The findings indicated that while the hydrodynamic efficiency changed within 1% upon the inclusion of the serrated trailing edge, a significant alteration existed in vortex structures of the wake. More horseshoe and secondary vortices were generated since large-scale vortices induced by the duct were disrupted circumferentially. This phenomenon expedited the distortion and mixing of trailing-edge vortices, causing flow instability. Furthermore, the serrated trailing-edge structure led to noise reduction. Particularly in the 0-1000 Hz range, the sound pressure level behind the duct showed a maximum reduction of 4.43 dB.