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  • Cavitation phenomenon of marine propeller

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    Cavitation phenomenon of marine propeller

    1. Vortex cavitation

    Vortex cavitation occurs in the tip and hub. The instability of the free vortex sheet that appears in the blade along the edge of the blade, the two large vortices are rolled up at the end of the tail, forming a tip hole in the tip, and the vortex of the heel is a hub vortex. The lowest pressure in the vortex core, the cavitation is produced when the critical pressure is reduced.

    2.Bubble cavitation

    Bubble cavitation usually refers to the cavitation bubble, which is produced by the maximum thickness of the blade on the back of the blade. At this time, the angle of the blade is smaller, resulting in negative pressure peak. Bubble cavitation has little influence on the performance of propeller, but it has an erosion effect on the blade material.

    3.Laminar cavitation

    The laminar cavitation usually refer to the outer edge of the blade outside the edge of the edge produced was flake, the length of different. In the larger angle of attack when the most likely to produce such vacuoles. Super-vacuolar flow: If the vacuoles from the leaf section of the guide edge has been extended to casually, that is all the leaves of the hollow cover, affecting the performance of the propeller without erosion. Local vacuoles: If the vacuoles originate from the leading edge and end before the edge, there is a denudation of the propeller.

    4.The effect of cavitation on propeller performance

    The first phase cavitation has no effect on the hydrodynamic performance of the propeller, but the blade surface is denuded.

    The second phase cavitation affects the hydrodynamic performance of propeller, but no denudation of the blade surface.

    5. Measures to delay the occurrence of propeller cavitation

    (1).Starting from reducing the maximum decompression factor

    Reduce the pitch of the leaf with the adjacent section. The pitch of the single oar in the leaf part of the larger mix, easy to produce vacuolization phenomenon, it can be the root section of the pitch to reduce the appropriate, so that the maximum decompression coefficient of the place to reduce and easy to maintain a considerable leaf width to avoid thickness is too large. Using the bow section or pressure distribution is more uniform in other forms of surface is conducive to delay the generation of vacuoles. Increasing the propeller disk to reduce the average thrust per unit area, so that the back of the decompression coefficient on the back.

    (2).Start with improving the number of cavitation bubbles

    Increase the depth of the propeller as much as possible. Decrease the speed of the screw, that is, as far as possible choose low rotating speed of the host. Improve the machining precision of the blade. To improve the stern of the shape of the part and correct installation of propeller shaft position can reduce the influence of the oblique flow mixing flow nonuniformity, etc.

    (3). Other measures

    For high-speed ships, especially high-speed ships, the propeller cavitation is always inevitable. Generally for the following processing: allow blade on the cavity existence, in use process should be based on the erosion of exchange. High speed again, simply try to prompt it under the second phase vacuoles, known as the cavity (or called supercavitation) propeller design problem.

     

     

     

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