Major reductions in frictional drag are required for the practical employment of large very high-speed ships. Such ships are highly desirable for both national defense and for competitive commercial transport. These drag reductions have been achieved by the injection of microbubbles of air and also of long-chain polymers into the boundary layer. A little known fact, however, is that the energy cost of the supply and insertion of air bubbles or of the carriage of polymer approximately obviates that saved by the drag reduction - rendering the process impractical, to this point. Controlled emission of microbubbles into a water flow boundary layer appears to be a promising means to significant reduction of frictional drag on ships. Theoretical analyses and hypotheses require that particularly small (about 100 micrometers or less) gas bubbles be emitted and retained in particular laminae close to the wetted surface. Drag reduction economy requires that the quantity of gas emitted be very small. Here a design of a controllable microbubble emitter which meets both demands above is put forth. The two key requirements governing the design are pulsed operation, which expels a known volume of air during each cycle, and a known number of uniformly-sized micro-holes, which determines bubble number and therefore bubble diameter. A first, proof of-concept experiment with a modified pulsed-pressure design of the proposed microbubble emitter was carried out and shows promise.


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    Title :

    A controllable microbubble emitter


    Additional title:

    Ein regelbarer Mikroblasenerzeuger


    Contributors:


    Publication date :

    2005


    Size :

    9 Seiten, 16 Bilder, 3 Tabellen, 4 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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