(4) "Verification test by actual full-scale propeller" in order to verify the effectiveness of the propeller with the new blade section installed on actual vessel.
2. TEST CONCERNING STATIC CHARACTERISTICS OF SPECIAL TWO-DIMENSIONAL BLADE SECTION
It is considered possible that the root cavitation generation shall be restrained, if effect of angle of attack variation on lift variation could be decreased by applying the blade section with its trailing edge shape intentionally revised, whereby the pressure variation in accordance with angle of attack variation is reduced.
2.1 MODEL BLADE SECTIONS FOR THE TEST
Total six blade sections were designed, of two groups of elliptical sections and practical-use sections, in order to study the relation between the trailing edge shape and the lift characteristics. While the elliptical sections have no camber, with different thickness/width ratios; the practical-use blade sections have different trailing edge shapes, with constant camber (which is an imaginary camber value prior to the trailing edge shape revised) and the constant thickness/width ratio. Any of the blade sections are two-dimensional with the blade chord length of 200 mm and the blade width also of 200 mm. Table 1. shows principal particulars of these blade sections, and Figure 2. shows photographs of E2 and A3 appearances, being representative examples.
2.2 TEST PROCEDURE
The test was carried out at the cavitation tunnel of The Shipbuilding Research Centre of Japan. Figure 4. shows illustration of the measuring equipment. With the force acting on the blade measured by means of the dinamometer connected to the blade; the lift and drag acting on the model blade secions for the test were measured, under the measurement condition of Reynolds number of 5.0 × 105 in a non-cavitated condition, with the measurement ranged from the angle of attack of -2°up to ＋ 15°.
2.3 TEST RESULTS
The lift curve slope (variation ratio of lift coefficient (CL) against angle of attack(α) is indicated in Figure 3., being the test result. The decreased effect of angle of attack variation on lift variation is observed in three kinds among six kinds of the tested blade sections. Within the elliptical blade sections, Model E3 having the largest thickness/width ratio of 50% is outstanding. Among the practical-use blade sections, Model A3 with perpendicularly mixed staggered cut trailing edge shape indicates the gentler lift curve slope; whereas the Model A3 is peculiarly characteristic with a bend on the lift curve slope.
As for the drag, on the other hand, all of the models indicate approximately similar values, except for Model E3 of elliptical blade section which indicates remarkably large value. The conclusion obtained from our study on the characteristics of the special two-dimensional blade section is itemized below.
(1) It is possible for the lift curve slope to be changed by revising the trailing edge shape.
(2) With an elliptical blade section, lift curve slope can largely be made gentler, with the thickness/width ratio to be increased largerly.
(3) With the test conducted this time, it was not possible for us to find out a distinct correlation about thickness/width ratio and the lift curve slope.