Investigation of propeller characteristics with different locations of the rudder
Examensarbete för masterexamen
In designing a ship, propulsive efficiency is a parameter which always is tried to be kept as optimum as possible. An investigation in full scale and model scale of a ship including propeller and rudder, regarding the effect of changing rudder position on variation of propeller characteristics has been carried out. SHIPFLOW software was utilized to apply Computational Fluid Dynamic (CFD) techniques in order to compute the flow around the ship hull, propeller and rudder. Lifting line method which is coupled with RANS solver module of SHIPFLOW is used to simulate and also compute the propeller characteristics. Five different longitudinal rudder positions were investigated and compared to each other in order to determine the optimum longitudinal position of rudder. Furthermore, in model scale, for optimum longitudinal rudder position, one different transverse position of rudder was also evaluated. For computing propeller characteristics, SELFPROPULSION command was applied into computations in order to achieve balance between drag and thrust by adjusting the shaft RPM. In order to evaluate the accuracy of results for these two different scales, computed results for original rudder position in model scale and full scale were compared with test results and predicted results by ITTC 1978 method, respectively. Computed results in model scale, thrust and torque, show a good agreement with test results but obtained results from computations for full scale, such as delivered power and effective power seem to be over predicted compared to predicted results by ITTC 1978 method. Consequently, optimum rudder position was determined based on model scale results which are reasonably accurate compared to full scale computed results. The reason which made full scale computation results over predicted can be described regarding to grid resolution at the aft part of ship hull which is not compatible with propeller grids. This causes inaccurate interpolation between propeller and hull/rudder grids which concludes over predicted results for full scale.
Transport , Farkostteknik , Transport , Vehicle Engineering