Marine propeller acoustic modelling - comparing CFD results with an acoustic analogy method

Propeller noise and vibration is important in the design of ships in order to improve comfort, reduce signature or mitigate environmental impact. Since acoustic measurements are often difficult to perform in typical maritime experimental facilities, acoustic predictions based on numerical computations are attractive. We utilised an acoustic analogy method to make acoustic predictions based on postprocessing of a hydrodynamic computational fluid dynamics simulation. Computational grids were designed to improve the resolution of the pressure field away from the propeller. The local pressure at a field point was found to be more sensitive to grid refinement than integrated propeller performance coefficients. Although the predictions made using the acoustic analogy in general agree well with the pressure computed by the hydrodynamic code, they also suffer from sensitivity to the required input data (pressure, velocity and acceleration). For a probe located further away from the propeller, where the pressure amplitudes are smaller, numerical disturbances are seen, which could affect predictions. This highlights the need for a well-converged accurate hydrodynamic solution when using an acoustic analogy method. Visualisation of the acoustic sources not only confirms the dominant noise-generating effects but also allows the spatial distribution of the acoustic sources to be examined. This may be useful for future noise reduction studies.