454 



In Test Series I, the size anc3 material of the foil 

 section were not changed. The material was pure 

 aluminum, JIS H2102-2 {AL > 99.55?). 



In Test Series II (NACA 0015) the following items 

 were tested. 



(1) Effect of cavitation niimber, velocity, and 

 chord length, and the hydrodynamic character- 

 istics of the cavity flow, on the erosion 

 intensity. 



(2) Effect of material properties on the erosion 

 intensity. 



(3) Comparison of the soft aluminum and paint 

 test results. 



The test conditions are summarized in Table 1 . 

 The attack angle was a = 4° throughout Test Series 

 I and II. In Test Series I, the air content was 

 a/Os = 0.5, while in Test Series II it was initially 

 0.2 and increased gradually during the experiment 

 to a value of 0.4 by the end of the experiment. 



In Test Series I-D, before the test began, air 

 bubbles were injected into the cavitation tunnel 

 to control air bubble content of the water. Then, 

 the erosion test was completed to study the effect 

 of air content on erosion. 



Experiments with air injection from the foil 

 surface were also carried out to study the positive 



utilization of erosion prevention effect of air 

 bubbles. 



At the start of the tests , the water temperature 

 was about 25°C which increased during the high speed 

 tests, reaching a maximum temperature of 50°C. 



In addition to the erosion tests, measurements 

 of the hydrodyncimic characteristics such as cavity 

 length, pressure distribution etc., were completed 

 using a similar foil section made of stainless steel. 



Material and Heat Treatment 



In Test Series I the foil section material was pure 

 aluminiom (JIS H2102 , 99.5?), while in Test Series 

 II pure aliraiinum and two kinds of aluminum alloy, 

 JIS H4163-2 (AA 5056) and JIS H4163-5 (AA 6063) 

 were used. These materials were selected for their 

 low erosion resistance, good corrosion resistance, 

 and good machinability. The foil sections tested 

 were machined by a NC-milling machine and the surface 

 was smoothed by a buffing machine. The foils' 

 surface roughness was found to be less than 1 pm 

 in the virgin state. 



Since the foil surface was work-hardened, a thin 

 layer of the foil surface had a large degree of 



Table 1 Experimental Conditions 



JIS 

 AA 

 as 



Japanese Industrial Standards 



The Aluminum Association 



Saturated Air Content at 25°, 1 ata. 



