Effect of aspect ratio on the deformation of flexible marine propellers in a uniform inflow using a RANS-FEM coupling

Ship propellers operate in a non-uniform wake fields. This results in fluctuating propeller loading when rotating. These variations reduce the attainable propulsive efficiency and increase the risk of cavitation and underwater radiated noise. Flexible propellers enable passive blade deformation as a response to the inflow conditions. The flexural behaviour can be designed to suit the instantaneous inflow conditions. It is desired to deform the propeller such that the loading is reduced in regions where the axial inflow to the propeller is reduced.
The challenge is to design a propeller whith such behaviour. For certain operating conditions of the C4- 40 propeller, the blade deformation results in increased thrust, specifically in the tip region. This is undesirable as this would increase the blade loading in the wake-peak, which reduces the resistance to cavitation. Propeller loading is mostly influenced by the pitch and camber of the propeller blades.
The loading of skewed propellers causes blade twisting, resulting in a pitch reduction, mainly in the tip region. The increased thrust is then attributed to a cambering effect, where the camber of the propeller is increased due to blade loading. The camber increasing effect is undesirable as this contributes to an increase in thrust. Flexible propellers should be designed such that this effect is small with respect to the reduction in pitch, to reduce the blade loading when operating at lower advance ratios ( J ).
The aspect ratio of the blades can influence the twisting stiffness and cambering effect. The influence of blade aspect ratio on the blade deformations and resulting forces is investigated. The aspect ratio of the blades is varied by changing the number of blades for a same BAR of 40%. This makes the thrust levels comparable. The method and simulation setup are explained, followed by the simulation results where the effects on loads and blade deformation are analysed. The conclusion highlights the main findings and recommendations for future propeller design.