Experimental and Numerical Analysis of the Performance of a Marine Propeller in Oblique Flow
B. van Broekhoven (TU Delft - Mechanical Engineering)
D. Fiscaletti – Mentor (TU Delft - Ship Hydromechanics)
G. Jacobi – Mentor (TU Delft - Ship Hydromechanics and Structures)
T.J.C. van Terwisga – Graduation committee member (TU Delft - Ship Hydromechanics and Structures)
B. Vera Garcia – Graduation committee member (TU Delft - Ship Hydromechanics)
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Abstract
Wind assisted ship propulsion is one of the realistic options that are considered as alternative ways to propel a ship, with the goal of reducing a ship's emissions. With WASP, the propeller is still needed, but will be less loaded as wind energy takes over part of the required thrust force. Ships that sail are always under a small drift angle. This does not only affect the forces on the ship, but also the performance of the propeller. Previous research studies are mainly focussing on manoeuvring applications. However, an important difference is that the speed of the ship is close to zero here, whilst the drift angles are very high. The goal of this thesis is to experimentally capture the influence of small drift angles on propeller performance. Also, the influence of the advance ratio is studied, as this will vary, as it is dependent on the wind speed.
For the experiment, a gondola is used. The gondola was connected to the HexaPod to alter the position of the gondola and the propeller. The propeller was positioned downstream of the gondola, in pulling condition. The results of the experiments showed that the gondola upstream of the propeller affects the thrust and torque of the propeller for small drift angles. Therefore, measurements were also performed at pitch angles to avoid this influence.
The results show an increase in both thrust and torque for increasing pitch angle. Due to the high uncertainty, the increase is not significant for the smallest angle considered. For experiments performed at higher Reynolds numbers, these experimental uncertainties decreased, and they showed the same trend. Moreover, it was found that the advance ratio also influences the change in thrust and torque. This shows that a lightly-loaded propeller is more prone to fluctuations in the inflow than a highly-loaded propeller.
Lastly, a numerical analysis was performed to also capture the blade loads and the wake of the propeller. Here, an increase in torque was observed for increasing pitch angle. However, this was not the case for thrust. The results showed that thrust and torque on a single blade start to oscillate, also for small angles. The in-plane loads were observed, as a result of imbalance of side and vertical force. The wake also showed the inclination angle and the imbalance of the thrust generation during a propeller revolution.