Marine propeller underwater radiated noise prediction with the FWH acoustic analogy part 3: Assessment of full-scale propeller hydroacoustic performance versus sea trial data

Abstract

This paper assesses the full-scale The Princess Royal vessel Underwater Radiated Noise (URN) characteristics using a CFD method. Also, the cavitation extensions and propeller hydrodynamic characteristics are explored over a wide range of operating conditions. The numerical calculations were carried out using a hybrid method combining the DES and permeable formulation of the FWH equation. In the numerical calculations, two different permeable noise surfaces encapsulating the complete hull and only the propeller and its slipstream were utilised. In order to accurately solve the tip vortex flow and model the tip vortex cavitation (TVC) in the propeller slipstream, the developed V-AMR technique was applied in the numerical calculations together with the Schnerr-Sauer mass transfer model to model the cavitation. The results were validated with the full-scale measurements in terms of propeller hydrodynamic characteristics, cavitation extension and URN. The results showed that the sheet cavitation extensions predicted in the numerical calculations agreed with the sea trial observations despite the differences in the violent cavitation dynamics. Similarly, TVC was somewhat observed in the numerical calculations using the V-AMR technique with a lack of dynamics and extension in the propeller slipstream compared to the full-scale observations. The comparison of noise spectra at two different operating conditions, where similar cavitations were observed between the numerical calculations and full-scale observations, showed an agreement with the full-scale measurements. The lack of TVC and possible bursting phenomena predicted in the numerical calculations caused the underprediction of propeller URN levels up to 20 dB at certain frequencies over the noise spectrum at the lowest blade loading conditions. When the two different permeable noise surfaces were compared, it can be concluded that the permeable noise surface, encapsulating the complete hull, captures more noise information in the noise spectrum than the permeable surface, encapsulating only the propeller and its slipstream. Also, a more distinct spectral hump triggered by the tip vortex was observed using the permeable noise surface around the complete hull compared to one around the propeller. The results showed that the interaction between the cavitation and nonlinear noise sources occurring around the hull might influence the amplitude of the characteristic hump, apart from the possible hull interference on the ship hull and appendages induced by the propeller.