(4) Within the test conducted this time, it was observed with the blade section having perpendiculary mixed staggered cut trailing edge that the lift curve slope made distinctly gentler and its irregularity.
From the above, it was found out possible for the lift curve slope to be made gentler with the two-dimensional blade section's trailing edge shape made insensitive or non-sharp. It could be said that in view of the extent of the lift curve slope made gentler, being remarkable with an elliptical blade section having a larger thickness/width ratio, the aforesaid finding contains higher possibility leading to a remedial countermeasure of the cavitation generation itself.
3. TEST CONCERNING DYNAMIC CHARACTERISTICS OF SPECIAL TWO-DIMENSIONAL BLADE SECTION
This test was conducted so that the lift/drag characteristics should be studied for the case of the angle of attack to vibratory be varied with regard to the specially shaped two-dimensional blade section with its trailing edge shape changed from a conventional propeller's, in order that the characteristics of the blade section with its fuzzy trailing edge shape shall be applied to a propeller.
3.1 MODELS USED FOR THE TEST
The seven types of the models were used for the test, with one kind of a representative practical-use blade section (NACA00125 blade section) added on the six kinds used for the test concerning static characteristics mentioned in Chapter 2.
3.2 TEST METHOD
The model for the test was secured in the vibration apparatus installed within the cavitation tunnel, so that it should be vibrated at a constant angle of attack and a frequency. The physical strength was measured by a dynamometer equipped within the vibration apparatus. The test conditions were the common vibratory frequencies of 5 Hz and 10 Hz, the lift coefficient at the neutral position of 0, and at the single vibration amplitude of 10°.
The Reynolds number applied was 5 × 105, same with that for the test concerning static characteristics mentioned under Chapter 2. The test was carried out at the cavitation tunnel of The Shipbuilding Research Centre of Japan, an incorporated foundation, with measurements up to second component for the amplitude and the phase of the lift and drag. In the analysis, the force purely by water was obtained, with correction made to the errors by the mass influence on the vibration, referring to a similar test results made in the air, for eliminating such an influence.
