ALTERNATIVE METHODS FOR WAKE QUALITY ASSESSMENT

Results of research carried out at B.S.R.A. and elsewhere have indicated that the main causes of unsteady cavitation and the resulting after-end vibration are the non-uniformity of flow into the propeller and the heavy propeller-loading. The need to have criteria for the assessment of flow quality from a given velocity-distribution is evident, and in recent years efforts have been made to devise such criteria as well as to improve the flow quality. As part of the Propeller-Excited Vibration project recently carried out by B.S.R.A., research has been conducted into methods of assessing wake quality; the Authors summarise the results of this research. The methods of assessment may be divided into two groups: heuristic and analytic. Heuristic methods generally use only the axial velocity component and assess the flow quality by means of the variation of this component alone. On the other hand, analytic methods require all three components of the velocity, and their variations, and assess the flow quality by means of non-dimensional quantities related to flow kinematics and flow geometry. It is shown that, with present wake-survey techniques, analytic methods cannot be applied adequately because of insufficient data although their potential for representing flow quality is high. Criteria based on heuristic methods are therefore proposed, and the development by B.S.R.A. of such criteria, for assessing the quality of both the wake and the wake/propeller combination, is described and discussed. The basis of the develoment is the experience gained from ships in service with known vibration characteristics. Compliance with these criteria is expected to reduce the possibility of high levels of pressure due to cavitation, though it cannot be guaranteed that vibrations will not occur; however, if the wake criteria are not met, alterations to the afterbody form should be considered.

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  • Corporate Authors:

    International Periodical Press

    193 Heemraadssingel
    Rotterdam,   Netherlands 
  • Authors:
    • Odabasi, A Y
    • Fitzsimmons, P A
  • Publication Date: 1978-2

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Filing Info

  • Accession Number: 00178319
  • Record Type: Publication
  • Source Agency: British Ship Research Association
  • Files: TRIS
  • Created Date: Jul 19 1978 12:00AM