Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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Influence of the Cavitation Nuclei on the Cavitation Bucket when Predicting the Full-Scale Behavior of a Marine Propeller
Influence of the Cavitation Nuclei on the Cavitation Bucket when Predicting the Full-Scale Behavior of a Marine Propeller
Pages 839-850
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From page 839... ...
Several recent studies, such as the large one suggested by the 20th I11C and conducted in 1992 at the Grand Tunnel Hydrodynamique (GTH) of the Bassin d~ssais des Carenes, have allowed a precise correlation between cavitation inception for different types of cavitation on marine propellers and nuclei distributions (20th ITTC report)
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From page 840... ...
With a large increase in liquid tension, little change in cavitation inception was found for blade surface cavitation (sheet cavitation) , but, in the case of both tip vortex cavitation and travelling bubble cavitation, the nuclei measurements from the GTH standard Centerbody Venturi correlated with many observed trends.
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From page 841... ...
= 0 N/m2) Figure 3 represents this major result and leads to the conclusion Hat it is no longer possible to conduct meaningful cavitation tests without determining the complete nuclei distributions.
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From page 842... ...
This means that, for different nuclei distributions, the model results will be transposed exactly in the same way, without any water quality transposition parameter. Particularly, the four characteristic cavitation inception values corresponding to the four nuclei distribution generated during the GTH-I11C tests (Figure 1)
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From page 843... ...
The propeller model has a diameter of 274.1 mm and is installed in the CEIMM Tunnel test section with brackets on the main shaft inclined with 5°30 (Figure 5~. i= - ~ / ~ ~ ~ ~'t I_ FIGURE 5: PROPELLER TEST CONFIGURATION IN THE CEIMM CAVITATION TUNNEL The cavitation nuclei distributions are measured by a fully calibrated Centerbody Venturi similar to the one that is used during standard cavitation tests on the GTH.
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From page 844... ...
, T" l r ~ Pcr-Pv (N/m2) - 1 00000 - 1 0000 - 1 000 - 1 00 FIGURE 7: INFLUENCE OF THE OPERATING CONDITIONS ON THE CHARACTERISTIC NUCLEI DISTRIBUTIONS, DURING THE CEIMM TESTS The analysis of the above results shows a large influence of both the pressure value and the dissolved O2 content on the nuclei characteristics.
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From page 845... ...
Moreover, how can we transpose such a result to full-scale prediction, when the model free nuclei content changes with the operating conditions, which is not the case at sea, as the nuclei distributions will not directly depend on the advance velocity ? Moreover, during a normal procedure, several problems can happen' as, for example, the increase of dissolved air content during the tests.
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From page 846... ...
ANALYSIS Following the same analysis than proposed by Gindroz and Billet t2, 3] , to correlate nuclei distributions with cavitation inception data, there is an attempt to transpose the model cavitation bucket to a model "zero tension" one, using the nuclei distribution characteristics.
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From page 847... ...
, with the cavitation parameter, CIn, is determined for different nuclei contents, from the nuclei distributions measured during the CEIMM tests for each On - J point. Figures 14 et 15 represent the evolution of the normalized tension, At, for 4 different nuclei contents, resp.
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From page 848... ...
CONCLUSION The present study shows He direct influence of the hydrodynamic operating conditions of a standard cavitation tunnel on the characteristic cavitation inception bucket of a propeller. Careful attention must be taken when conducting cavitation tests, as the final results can include important effects from the evolution of the nuclei with the tunnel 848
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From page 849... ...
L., "Cavitation Nuclei Measurements", Proceedings of the International Symposium on Cavitation Inception. ASME WAM, 1984, New Orleans.
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From page 850... ...
E., Kuhn de Chizelle, Y., "Cavitation Nuclei Concentrations and Event Rates", Internal Report, CALTEC, Pasadena, CA, July 1992.
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