Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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A Comparitive Study of Conventional and Tip-Fin Propeller Performance
A Comparitive Study of Conventional and Tip-Fin Propeller Performance
Pages 930-945
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From page 930... ...
Both propellers suffer from slight suction side sheet cavitation in the inhomogeneous wake field behind the ship. The tip-fin propeller suffered a little more from cavitation than the conventional propeller which gave rise to maximum, measured, first-order pressure pulses of 13 to 1.4 times those of the conventional propeller.
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From page 931... ...
The examination reported in the present paper was conducted to see, whether the promises would be fulfilled for a tip-fin propeller designed for a given ship. The idea was to make a complete tip-fin propeller design computation and model tests consisting of resistance, open-water, self-propulsion and cavitation tests and compare and analyse those results with similar results for the conventional propeller, designed for the same ship.
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From page 932... ...
In addition to ship and propeller models being available they were selected for the comparative study out of consideration for the propeller loading, which was moderate (Cn, = 1.545) , a wake field which was typical for a ship of that size and displacement and a combination of thrust loading coefficient and advance ratio which was favourable for both the conventional and tip-fin propeller.
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From page 933... ...
Although it was expected that the effective wake field, the thrust deducE`igure 3 Tip-fin propeller. 933 tion fraction and the relative rotative efficiency would be slightly different due to the modified radial distribution of loading of the tip-fin propeller, the same values as for the conventional design were used.
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From page 934... ...
, TCVD 0.04 . O ~Conventionat ~¢ /7~ _ - 0.` 0.6 Figure 5 Spanwise distribution of loading in form of chordwise integrated circulation for conventional propeller and tip-fin propeller as function of radius, length of mid-chord-line arc-length s and s`,.
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From page 935... ...
The tip geometry was designed on the basis of earlier model experiments as well as experience with a vast number of theoretical design studies carried out using the procedure outlined in the previous section. This gave information on the shape of the tip, i.e.
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From page 936... ...
Uncorrected model test results Rc = 5.0 5.6.105. To 0.65 0 60 0.55 n 50 SELF-PROPULSION TESTS Results of the self-propulsion tests in form of a power prognosis is shown in Figure 8.
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From page 937... ...
The differences in wake fraction and thrust deduction coefficients result in hull efficiencies that are higher for the tip-fin propeller. But the product of hull efficiency and relative rotative efficiency is almost the same for the two propellers when using the ITI C-method.
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From page 938... ...
cavitation over the curved transition area between blade and tip fin, was observed in the earlier model tests with the tip-fin propeller designed for open water [91. Note that the tip-fin propeller exhibited very little, if any, tip vortex cavitation.
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From page 939... ...
tip-fin propeller, (lower) reference propeller Pressure side Cavitation 2 0 2 5 3 0 0..n Table 4 Conditions for cavitation tests with 237.5 mm diameter propeller models at rate of revolution appr.
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From page 940... ...
Conventional propeller Blade position 0° Sign = 2.47 KT = 0.264 (in = 2.37 KT = 0.255 J = 0.619 Figure 11 Cavitating tip-fin and reference propellers.
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From page 941... ...
Conventional propeller Blade position 40° Moan = 2.47 IT = 0.264 J = 0.615 In = 2 37 IT = 0.255 J = 0.619 Figure 11 Cavitating tip-fin and reference propellers.
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From page 942... ...
Results of pressure level measurements are shown in Table 5 As expected from the observations of cavitation extent the tip-fin propeller gives the largest pressure levels for the same condition, and the service condition has the largest pressure levels for both tipfin and reference propeller. This applies to the first
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From page 943... ...
In the self-propulsion tests minor differences in thrust deduction and wake fraction coefficients and in relative relative efficiencies were found for the two propellers. In the inhomogeneous wake field both propellers suffered from suction side cavitation around 12 o'clock blade position.
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From page 944... ...
and van Gent, W "Model Testing of an Optimally Designed Propeller With Two-Sided Shifted End Plates on the Blades", Proceedings of Nineteenth Symposium on Naval Hydrodynamics, National Academy Press, Washington, D.C.
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From page 945... ...
A decrease in thrust loading coefficient relative to the design value for the given propeller is obtained by increasing the advance ratio. The blade sections will then experience less inflow angle and lift, and also less induced drag.
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