Evaluation of 'Fuel saving devices'
by M.Sc. (Naval Architecture), Phd. Claus D. Simonsen, Senior Specialist at FORCE Technology
The purpose of the present project has been to study the possibility of determining – by means of RANS-CFD - the relative power or efficiency gain obtained by substituting an original conventional propeller-rudder configuration of a given vessel with a different and more efficient rudderpropeller configuration (Fuel Saving Device).
As the overall efficiency of a given vessel is given by
where R is the bare hull resistance, V the vessel speed, Q the propeller torque and n the propeller number of rotations per time, the question boils down to whether the relative difference of the propeller efficiency between two alternative rudder-propeller configurations (here indexed 0 and i)
can be determined with a ‘satisfactory accuracy’. Thus, the main questions are:
1) Can a given overall trend: ‘better or worse?’ be predicted?
2) How accurate is the prediction?
In order to answer these questions, there are two tasks to be performed:
1) Determination of torque for a given n.
2) Determination of n at self-propulsion point
In the present project we have focused on the first part of the problem and given the second part less attention (to which only some hints on how to proceed will be given). It is important however to notice that these two tasks are of equal importance, which furthermore means that we cannot expect a complete tool for predicting the effect of fuel saving devices within the limits of the present project.
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