Measurement of Pressure Distribution on a Full Scale Propeller

Abstract

This paper describes the first development of sophisticated pressure measurement technique for a full scale propeller and the success of the measurement. First of all, the special pressure pick-ups with Helmholtz chamber were designed. The full scale measurements were carried out on the training ship “SEIUN-MARU”. Six pressure pick-ups were equipped at each of four propeller blades. The pressure signals were transmitted from the pressure pick-ups on the propeller blades through slip-rings to FM receivers and analyzed using static pressure calibration data obtained in the dock before the voyage.This ship was operated so carefully that the working conditions at each propeller revolution rate were kept constant, that is, KT = 0.210. Then, the measured non-dimensionalized pressure distributions were similar at each condition, except cavitation regions. Except the lowest revolution rate, sheet cavitation or tip vortex cavitation was observed and the influence of cavitation of other blades on the pressure measurement was found out. The present measurement techniques have the accuracy of ±0.03 kg/cm2. By the pressure coefficient, it amounts to ±0.3 at 70 RPM and ± 0.07 at 149 RPM, respectively.The measured pressure distributions were compared with the theoretical ones obtained by the existing lifting surface theory. In this calculation, the estimated nominal wake distribution was employed, including the tangential wake based on the measurement in a towing tank. Excellent agreements with theory were found at most of the measurement points, especially the fore part of the blades. These results clearly demonstrate that the use of this estimated wake and the lifting surface theory with the concept of the equivalent two-dimensional profile is quite reasonable for a conventional propeller principally. Near the angular position of the top, some discrepancies between the measurements and theory were observed probably due to the deformation of the nominal wake and the leading edge separation. The present full scale measurements indicated that there still exist some problems on the lifting-surface theory and the use of nominal wake.These measurements also confirmed that the measured pressure in the sheet cavitation region was nearly equivalent to the vapor pressure at each working condition.The present study has provided a number of invaluable standard data to validate the numerical computational techniques on marine propellers at high Reynolds number.