The effect of propeller geometry in respect to efficiency, pressure pulses and generated noise, at a certain design point

Abstract

Three propellers, each with different blade number have been designed according to the design point of a cruise ship. The number of blades varies between four and six. The propellers have been compared against each other in respect to efficiency, induced pressure pulses and noise generation. Additionally the effect of skew and rake has been taken into account.

Result shows that the optimal diameter is smaller, the more blades the propeller owns. The induced pressure pulses are clear1y largest for the four-bladed propeller, but it has also the highest efficiency, if the pitch distribution is similar for each propeller. The efficiency can be improved by increasing the pitch close to the tip and hub, but this can however cause broadband noise. The smaller propellers have larger tip clearance, which is beneficial for minimizing pressure pulses.

By introducing skew to the propeller blades, efficiency tends to increase linear1y, and pressure pulses due to loading decreases. A small rake angle can improve the efficiency slightly and as well cause a reduction in induced pressures. Forward rake is more beneficial according to improve efficiency, while aft rake reduces the pressure pulses.