Investigation of propeller characteristics with different locations of the rudder

Sammanfattning: In designing a ship, propulsive efficiency is a parameter which always is tried to be kept asoptimum as possible. An investigation in full scale and model scale of a ship includingpropeller and rudder, regarding the effect of changing rudder position on variation ofpropeller characteristics has been carried out. SHIPFLOW software was utilized to applyComputational Fluid Dynamic (CFD) techniques in order to compute the flow around the shiphull, propeller and rudder. Lifting line method which is coupled with RANS solver module ofSHIPFLOW is used to simulate and also compute the propeller characteristics. Five differentlongitudinal rudder positions were investigated and compared to each other in order todetermine the optimum longitudinal position of rudder. Furthermore, in model scale, foroptimum longitudinal rudder position, one different transverse position of rudder was alsoevaluated. For computing propeller characteristics, SELFPROPULSION command wasapplied into computations in order to achieve balance between drag and thrust by adjustingthe shaft RPM.In order to evaluate the accuracy of results for these two different scales, computed results fororiginal rudder position in model scale and full scale were compared with test results andpredicted results by ITTC 1978 method, respectively. Computed results in model scale, thrustand torque, show a good agreement with test results but obtained results from computationsfor full scale, such as delivered power and effective power seem to be over predictedcompared to predicted results by ITTC 1978 method.Consequently, optimum rudder position was determined based on model scale results whichare reasonably accurate compared to full scale computed results. The reason which made fullscale computation results over predicted can be described regarding to grid resolution at theaft part of ship hull which is not compatible with propeller grids. This causes inaccurateinterpolation between propeller and hull/rudder grids which concludes over predicted resultsfor full scale.