172 



FIGURE 3. Static pressure distribution on 

 the hull surface (GBT-125) . 



Experimental Examinations of Boundary Layer Assump- 

 tions and Semi-Empirical Equations 



Boundary Layer Assumptions 



can be assumed to have separated near S.S.ii.) There 

 the concept of boundary layer itself should be dis- 

 carded. 



It can be safely pointed out that the pressure- 



The usual first approximate calculations of the 

 boundary layer were carried out under the assump- 

 tion that the static pressure is constant across 

 boundary layers and is equal to the inviscid flow 

 pressure. These assumptions are open to experimental 

 examination when the boundary layer thickness is 

 not -thin, especially in the case of ship-like bodies. 



Static pressure distributions on the hull sur- 

 face along streamline Nos . 5, 7, and 11 are shown 

 in Figure 3 with calculated potential flow pressures. 

 Potential flow calculations were carried out by the 

 well-known surface-source method [Hess and Smith, 

 (1962)] representing the hull by 254 x 2 small rec- 

 tilinear panels. Static pressures while being 

 towed onward are in good agreement with those calcu- 

 lated, except near the stern, where pressure has 

 not recovered and is slightly low. However, towing 

 astern shows good agreements even near the stern. 

 This means that displacement effects of the boundary 

 layer are appreciable near the stern. 



Figure 4 shows static pressure profiles in the 

 boundary layer . It was observed that pressure pro- 

 files are almost constant across the boundary layer 

 except for some positions where the pressure is mono- 

 tonically increasing or decreasing in that normal 

 direction. The tendencies of increments are signif- 

 icant at 3.3.1*2 or S.S.lSj of streamline No. 11. This 

 can be referred to the centrifugal force due to the 

 small radii of curvature of the bilge keel. On the 

 other hand, a decrease can be found for all the 

 streamlines at 3.3.^2 or S.3.^, which maybe the 

 effect of separation. (As described later, flow 



*Static pressure on the hull surface does not agree with that 

 of Figure 3. While the measurements whose results are shown 

 in Figure 3 were carried out in the towing tank, those shown 

 in Figure 4 were in the circulating water channel. The 

 discrepancies are all due to this difference in experimental 

 conditions; the cross section of the circulating water chan- 

 nel is restricted to 1200mm x 820mm and pressure is under- 

 estimated. 



Mr 



STREAHIWE HO. 5 



<i ; 



u 



-0.2 -0.2 



• 1 

 'J 



I 



X 3 c p 



?("">) STREAW.1WE WO. 9 



Mr 



,1 'I 



J_ 



LlllL 



5(nim) 



-0.2 -0.2 -0.1 



STREAHIWE WO. 



X^ 



TT 



'i: 



i ' / t • » 



FIGURE 4. Static pressure profiles in the boundary 

 layer (GBT-125) . 



