1991 Volume 1991 Issue 170 Pages 111-123
In the previous paper, authors have developed a new technique to measure the pressure distribution around the blades of a full scale propeller. The full scale measurements were performed on the conventional propeller, CP in short, of the training ship “Seiun-Maru”. From the results of full scale measurement, the measured pressure distributions were similar at each propeller loading condition, except cavitation region. Comparing with an existing propeller lifting surface theory, good agreements were found at most of the measurement points on the back side except near the propeller tip.
This paper describes the measurement of pressure distribution on a highly skewed propeller, HSP in short, of the same ship “Seiun-Maru”. First of all, the special pressure pick-up was improved taking account of the experience in the previous measurement. The same measurement instruments were employed. The measurements were also performed with the same procedure as the previous ones under several working conditions of propeller revolution rate 70, 90, 110 and 149 rpm. At the propeller revolution rates more than 110 rpm, the thrust coefficient KT and the advance coefficient J are 0.190 and 0.66, respectively. The accuracy of the present measurement was estimated to be the same as that of the previous one, i. e, ± 0.03 kg/cm2.
The measured pressure distributions were compared with the theoretical one with using an estimated nominal full scale wake distribution. Excellent agreements with the theory were found at most of the measurement points, especially in the fore part of the blades. These results indicate the usefulness of the lifting surface theory and the estimated wake for a highly skewed propeller in full scale.
On the other hand, the following unforeseen findings were obtained. The measured pressure at 90% radial position tends to decrease toward the trailing edge and completely differs from the theory. This suggests us the hydrodynamic load in the vicinity of the trailing edge at 90% radial position was remarkably heavier than that predicted by the theory. This cyclic load might cause the break-off of the propeller tip due to rapid fatigue crack growth, if a propeller blade is damaged at the trailing edge.
The measured pressure in the region of sheet cavitation on HSP was higher than the vapor pressure while that on CP was equal to or lower than the vapor pressure.
The present full scale measurements indicated that there still exist some problems on the existing propeller theory and some improvements are necessary on the modelling of a propeller theory including separation vortex from the leading edge.
The present measurement of pressure distribution on both propellers also provides us a number of invaluable standard data to develop and validate a new propeller theory.
