BLADE FREQUENCT HARMONIC CONTENT OF THE POTENTIAL WAKE OF SINGLE SCREW SHIPS

摘要

Using thin ship theory, approximate formulas are developed for the axial velocity at the propeller plane. Harmonic analysis of the flow variation at one radius is carried out to provide the harmonic content at the propeller plane of U-and V-sectioned hull forms and a strut of infinite draft for which the exact solution is known. These results are compared with the harmonic content obtained from experi¬mental model data. The potential wake harmonics are compared with those obtained from model tests and are found to be much smaller. An estimate is made of the harmonic content of the viscous wake using modified flat plate boundary layer theory which shows agreement with the experimental results. Vibra¬tory thrust computations for a specific propeller, using the wake velocities of the U-and V-sectioned hull forms, are in¬cluded to indicate, from a practical standpoint, magnitudes and effect of change of hull form.nIt is concluded that the potential flow contribution to the harmonic content of the flow at the propeller plane and the resultant vibratory thrust is of an order of magnitude smaller than that which arises from viscous effects.