Eighteenth Symposium on Naval Hydrodynamics (1991) / Chapter Skim
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Cavity Thickness on Rotating Propeller Blades - Measurements by Two Laser Beams
Cavity Thickness on Rotating Propeller Blades - Measurements by Two Laser Beams
Pages 319-330
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From page 319... ...
The essential feature of the new procedure is the use of two laser beams of constant intensity intersecting at the surfaces of the cavity and of the propeller blades, resp. INTRODUCTION As a result of the efforts to increase the delivered power of ship propellers, to build lighter hulls and to use propellers with larger diameters ship hull vibrations are an increasing problem.
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From page 320... ...
In order to hit the cavity where the measuring direction penetrates the cavity surface, the laser beam, which initially is positioned on the blade surface, has to be shifted parallel with the propeller shaft. The cavity thickness then follows from the shift with regard to the measuring direction and the blade geometry (Fig.l)
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From page 321... ...
The preliminary tests have shown that the laser beam always can be ob served clearly and sharp-edged where it is crossed by the propeller blades and thus strikes the solid blade surface - provided that adequately long light pulses are used. This led to the idea to use two permanent laser beams intersecting in one point, instead of a single pulsated beam, and to utilize the beam intersection, which in the interesting propeller regions always can be clearly seen, as a pointer tip.
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From page 322... ...
, divides the entering laser beam into two convergent beams intersecting in one point. For posi .
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From page 323... ...
Following the positioning, the light intensity is increased again and the adjustment of the lower translation stage is noted down. Finally the tunnel pressure is lowered again down to the required value to get cavitation and the beam intersection is shifted into the cavity surface with the aid of the lower stage.
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From page 324... ...
(p =33oo ~ =34Oo \, ,,~ ~ =10° (,t'4, ,/,\) ~ ~ =20° Fig.7 Measured cavity thicknesses of propeller No.
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From page 325... ...
HSVA `076 (isometric representations 325
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From page 326... ...
~ JO ~ ~ \~ ~ =10° And ~ =40 TV, \`,;~w ~ = Coo Fig.9 Measured cavity thicknesses of propeller No. HSVA 2054 (isometric representation)
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From page 327... ...
To facilitate the calculation of the cavity volume as a step function, the cavity thickness measured in direction of the propeller shaft has been converted to the direction normal to the blade surface. The required angles were determined experimentally by reflecting a laser beam at the blade surface.
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From page 328... ...
cavity thicknesses 328
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From page 329... ...
and Frivold, H., "Low Frequency Variation of the Surface Shape of Tip Region Cavitation of Marine Propeller Blades and Corresponding Disturbances on Nearby Solid Bound-aries", Proceedinas of the llth SYmoo-sium on Naval Hydrodynamics, London 1976, pp.
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From page 330... ...
Kinnas Massachusetts Institute of Technology, USA The paper offers valuable experimental information of unsteady cavity shapes, which can be used to validate existing analytical techniques. I would like to address the following two points though: (a)
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