Development of a numerical simulation model of the forces on ventilating propellers

Abstract

Ships and marine structures operating with propellers will from time to time experience severe, instantaneous thrust and torque losses to air drawing to the propeller. This is known as ventilation, and it may cause serious issues for vessels operating at rough seas. Not only will ventilation lead loss of propulsive power, the dynamic and fluctuating nature of the phenomenon may cause propeller racing, leading to damages to the mechanical parts of the engine. There has been a large amount of research on ventilating propellers over the last few years. But there is still a need for a simple mathematical model of the forces at stake during ventilation. As part of this thesis effort has been made towards creating a mathematical model able to capture the important physical aspects of propellers during ventilation. The basis for is a complete momentum theory, able to capture both axially and tangentially induced velocities. Comparing the mathematical propeller model against experimental results, as well as against more established programs such as OpenProp has shown that the numerical method is not of very high accuracy. Testing propeller geometry against experimental results did in fact yield quite large errors. On other occasions the resulting forces calculated by the numerical model coincide fairly well with other solutions. Even though the final numerical model is quite simple, and prone to inaccuracies it is still able to capture some of the important aspects of ventilating propellers.