Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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A New Way of Stimulating Whale Tail Propulsion
A New Way of Stimulating Whale Tail Propulsion
Pages 946-958
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From page 946... ...
Today, advanced ships demand a well-balanced compromise between the main requirements for a ship propeller, such as: high efficiency, minimum danger of cavitation, noise and erosion, minimum propeller excited vibratory forces, good stopping abilities and manoeuvrability, minimum vulnerability and low initial And maintenance costs. During the last decades the non-conventional propulsion devices have shown to be competitive to the screw propeller.
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From page 947... ...
The trochoidal propeller with a horizontal axis, 'Whale Tail Wheel' in the following, is a combination of the tail propulsion of a living creature and the wheel, invented by mankind. The choice of the dimensions of the Whale Tail Wheel can lead to a minimum thrust loading per unit envelope area and consequently to the optimum of the maximal efficiency curve of the trochoidal propeller with a horizontal axis.
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From page 948... ...
From a comparison of the ideal efficiency and the open water efficiencies of the propellers, the importance of the ideal efficiency becomes evident. The maximum propeller open water efficiency appears to be roughly some 70~o of the ideal efficiency over the plotted range of thrust loading coefficients.
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From page 949... ...
Wheel dimensions Equivalent to the propeller disk area or propeller diameter is the Whale Tail Wheel envelope area An, that is projected in the plane oriented at right angles with the propulsor heading. Because of the geometry of the cycloidal propeller, this area is not only determined by the orbit diameter of the blades, but also by the span of the blades.
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From page 950... ...
A similar restriction in blade trajectory type holds for the cycloidal propeller with pitch ratios e |
From page 951... ...
This expectation is based on He lower thrust loading, causing lower inflow velocities to the blades and the anticipated smaller variations in blade angle of attack for the Whale Tail Wheel. Only in the lower part of the blade orbit, a high rate of change in angle of attack .
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From page 952... ...
Throughout the computation, all time derivatives have been neglected, as is the case in the model of Brockett. It is to be noted however, that especially near positions in the blade orbit, where the blade angle of attack rapidly changes, these time derivatives may have a non-negligible effect on especially torque.
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From page 953... ...
10. Also plotted in this figure is the blade angle path of a pure cycloidal blade motion of similar pitch value (e = 0.83)
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From page 954... ...
It is expected however that the trend in the angle of attack with blade position remains unaltered, and therefore the blade angle of attack was set at a constant 4 deg over the major part of the blade orbit. Adaptations to this constant angle of attack were only necessary in both the top and bottom position of the orbit.
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From page 955... ...
The open water efficiency is roughly some logo points higher than for the propeller at the same loading coefficient.This advantage should at least partly be attributed to the lack of 3D flow effects on the foils of the Whale Tail Wheel. It should however be noted that a comparison at equal thrust loading coefficient is interesting from the point of view of hydrodynamics, but that it is not a relevant comparison for realistic designs.
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From page 956... ...
Cavitation may occur in the lower part of the blade orbit, where a high blade pitch rate occurs. The very low thrust coefficient of the Whale Tail Wheel, combined with the control of blade angle rate by an adjustable eccentricity of the blades along their orbit allow for a control of cavitation inception and developed cavitation phenomena at the cost of only small efficiency reductions.
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From page 957... ...
This elimination may lead to a substantial operational reduction of the cargo-handling costs. The extremely light propeller loading of the Whale Tail Wheel Eccentricity leads to a simplification of the ship's afterbody (largely 2-dimensional)
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From page 958... ...
I - span of blade p - mass density of water n - propulsor rotation rate ~ - blade orbit angular position R - radius of blade circle ~ - angular rotation rate [radls] All quantities in SI-units 958
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