Marine fouling roughness effects on pump-jet hydrodynamics and flow noise

Marine hydraulic machinery is highly susceptible to biofouling, which alters surface roughness and degrades both hydrodynamic and acoustic performance during long-term operation. Using barnacles as representative fouling organisms, this study systematically examines the effects of fouling size and spatial distribution on pump-jet propulsion through high-fidelity numerical simulations. The flow field is resolved using the improved delayed detached eddy simulation (IDDES) turbulence model, and flow-induced noise is predicted via Lighthill's acoustic analogy. Variations in barnacle coverage and attachment locations are evaluated in terms of thrust, torque, wake characteristics, and acoustic radiation. Results show that barnacle-induced roughness disrupts boundary-layer development, intensifies turbulence, and promotes flow separation, leading to measurable performance deterioration. Under severe fouling (Type B2), the propulsion efficiency decreases by up to 29.6%, while the overall sound pressure level increases by 16.35 dB. Even mild fouling produces notable degradation, with efficiency losses of 3%–8% and a noise increase exceeding 10 dB. Larger barnacles and irregular distributions further amplify wake vortex strength and broaden low-frequency noise components, particularly at blade-passing harmonics. These findings quantify the combined hydrodynamic and acoustic penalties caused by marine biofouling and provide a theoretical basis for antifouling design, performance prediction, and maintenance planning in marine propulsion systems.