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Open AccessArticle

Transitional Flow on Model Propellers and Their Influence on Relative Rotative Efficiency

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J. Mar. Sci. Eng. 2019, 7(12), 427; https://doi.org/10.3390/jmse7120427
Received: 31 October 2019 / Revised: 18 November 2019 / Accepted: 19 November 2019 / Published: 25 November 2019
Unexpected low value of the relative rotative efficiency ηR is sometimes noted when scaling the towing tank model-test result with the ITTC-78 method to obtain the propulsive efficiency factors of propellers. The paper explains the causes of this phenomenon. The boundary layer state of three propellers was studied by a paint test and a RANS method. The paint tests showed that the propellers in behind conditions at low Reynolds number (Rn) are covered mainly with laminar flow, which is different from open water tests conducted at a high Rn. Apart from that a moderate difference in Rn between the open water and the self-propulsion test may lead to a low ηR value, the paper points out that flow separation in behind conditions could be another significant reason for the drop of ηR for some propellers. Therefore, two factors will lead to an unexpected decrease of ηR: (1) A slightly lower open water torque interpolated from an open water test carried out at a high Rn and (2) a slightly higher torque in a self-propulsion test due to laminar flow separation near the trailing edge. The phenomenon is caused by the Rn scaled effect and closely associated with design philosophy like the blade section profile, the chord length, and chordwise load distribution. View Full-Text
Keywords: Reynolds number; propeller; laminar/transitional/turbulent flow; scale effects; transition model; separation; paint test method Reynolds number; propeller; laminar/transitional/turbulent flow; scale effects; transition model; separation; paint test method
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Li, D.-Q.; Lindell, P.; Werner, S. Transitional Flow on Model Propellers and Their Influence on Relative Rotative Efficiency. J. Mar. Sci. Eng. 2019, 7, 427.

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