| Popis: |
Propeller performance is typically considered under clean conditions, despite the fact that fouling is an inevitable phenomenon for propellers. The main objective of this study is to investigate the effects of roughness due to fouling on the performance of a propeller using a CFD simulation in conjunction with the roughness function model. A simulation of a clean propeller is verified for a five-blade propeller model using existing experimental results. A roughness function model is then suggested based on existing measured roughness data. The simulations are extended for the same propeller under varying severities of roughness. Initially, it is concluded that KT and ηo gradually decrease with increasing fouling roughness, while KQ increases, compared to smooth propeller. For instance, at J=1.2 for medium calcareous fouling, KT is reduced by about 26%, KQ increases by about 7.0%, and ηo decreases by 30.9%. In addition, for the rough propeller, the extra power required is defined as the specific sea margin (SSM) to compensate for the power loss. A slight roughness causes a large decrease in ηo. A propeller painted with foul-release paint and an unpainted propeller are found to require 2.7% SSM and 57.8% SSM over four years of service, respectively. Finally, the use of foul-release paints for propeller painting is strongly advised. |
