COMPIT 2010 in Gubbio - TUHH

Before the beginning of the propeller optimisation a grid sensitivity study was made to analyse the
influence of the different grid strategies on the results. So the thrust coefficient was calculated for a
propeller geometry with three different grid configurations. The calculated results and applied grid
resolutions are presented in Table 1. Due to the considerable reduction of calculation time (about 40
%) and the limited influence on the accuracy of the estimated thrust (less than 1%), grid configuration
III was selected for the further calculations.
Fig.3: Propeller design “Optim I”
Fig.4: Propeller design “Optim II”
The optimised propeller geometries I and II are shown in Figs.3 and 4. Propeller I is optimised by
employing a single criterion target function without taking into account the minimisation of the thrust
amplitude of a single propeller blade. This additional criterion is considered during the optimisation of
propeller II. In both cases the NSGAII optimisation algorithm is used.
Fig.5: Radial distribution of pitch ratio
Fig.6: Radial distribution of chord length ratio
Table 2: Comparison of two propeller designs
Propeller “Optim I” Propeller “Optim II”
Cavitation: 0.40 % 1.80 %
Efficiency: 66.3 % 63.6 %
Amplitude / Target Thrust: 35.6 % 31.6 %
The calculated radial pitch and chord length for the two propellers are shown in Figs.5 and 6. While
propeller I has a relatively high blade area and a low pitch, the propeller II shows the vice versa
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