Influence of Blade Hub Diameter Ratio on the Acoustic Performance in a Shaftless Pump-jet Propulsor

The complex internal structure of a shaftless pump-jet propulsor presents significant challenges for reducing flow-induced noise and improving hydrodynamic performance. In this study, the flow field was numerically simulated using the RNG k–ε turbulence model, and the numerical approach was validated against experimental measurements. Fast Fourier Transform (FFT) was applied to identify dominant noise components, and flow-induced noise was predicted using a hybrid computational approach based on Lighthill’s acoustic analogy as the blade hub-to-tip diameter ratio was varied from ۰.۲۰ to ۰.۲۵. The results indicate that variations in the hub-diameter ratio have a negligible effect on energy performance. Flow-field analysis reveals that, with increasing hub-diameter ratio, low-Ω regions in the wake extend axially, wake vortex coherence weakens, and central vortex intensity decreases, leading to a more uniform outlet velocity distribution. These results indicate that the hub-diameter ratio plays a significant role in wake evolution and outlet flow organization. Acoustic analysis further confirms that twice the shaft frequency remains the dominant tonal component across all hub ratios, with blade–wake interactions identified as the primary noise source. When the hub-diameter ratio increases to ۰.۲۵, the amplitude of internal flow noise decreases, leading to a ۲.۴۲% reduction in the sound pressure level (SPL) at twice the shaft frequency and a ۰.۵۱% reduction in overall sound pressure level (OSPL). Additionally, the axial SPL distribution exhibits a consistent downward trend with increasing hub ratio. These findings establish a quantitative link between hub geometry, wake vortex dynamics, and acoustic radiation, providing theoretical insights into flow-noise generation mechanisms and offering guidance for the combined hydrodynamic and acoustic optimization of shaftless pump-jet propulsors, thereby supporting the development of quieter and more stealth-efficient underwater vehicles.

کلیدواژه ها:

Shaftless pump-jet propulsor ، Blade hub-to-tip diameter ratio ، Flow-induced noise ، Vortex intensity ، Sound pressure level