From observations of fast swimming species in the animal kingdom we know that the flapping hydrofoil can be a very effective means of propulsion. There is also evidence suggesting that fish can manipulate the vorticity by skillful use of the caudal fin. In this report it was tried to answer the following questions: how does the foil interact with such ambient concentrations of vorticity, and what potential benefits can be reaped from such interactions ? The quantitative results are in the form of a parameter study of the conventionally defined propulsive efficiency. It was found that efficiency can exceed 100 % when the foil motions are on the order of half the vortex street width and the vortex street is strong enough to correspond to a drag coefficient of 0.4. In all but one case it was found that the timing, or phase, of the foil motion should be such that it is brought in close contact with the individual vortices in the inflow, a fact that is also indicated by previously published experiments. It was also considered whether the foil could regain a net amount of energy from the oncoming flow. This is indeed the case during optimal conditions, although the net gain is small compared with the energy in the Karman vortex street. The structure of the flow in the combined wake downstream of the foil is also of interest. A variety of interaction modes can be obtained by adjusting the parameters that control foil motion. Different energy levels in the combined wake are associated with different input power to the foil.


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    Title :

    Efficient foil propulsion through vortex control


    Additional title:

    Wirksamer Tragflächenantrieb durch Steuerung der Wirbelströmung


    Contributors:

    Published in:

    AIAA Journal ; 34 , 11 ; 2315-2319


    Publication date :

    1996


    Size :

    5 Seiten, 4 Bilder, 1 Tabelle, 15 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




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