results with previous boundary layer calculation methods and experi- 



1,21 

 ments. Earlier calculations of the Lucy Ashton double body boundary 



layer by von Kerczek showed that crossflow is small almost everywhere on 



the hull. 



Figure 3 shows several streamlines computed by slender body potential 



flow theory. In bottom, elevation, front, and rear views on the Lucy 



Ashton double model. Computed boundary layer results will be shown along 



these streamlines. Figures 4a-4d show a comparison of the distribution of 



the streamline momentum thickness 9-.-,, along the streamlines 1, 6, 10, and 



13 shown in Figure 3b, as computed by the present complete crossflow 



method and the small crossflow method of von Kerczek. Figures 5a-5d show 



the distribution of streamline skin friction coefficient C and Figures 6a- 



6c show the distribution of the crossflow angle in radians along these same 



streamlines. Note from Figures 3 through 6 that there is little difference 



in the boundary layer characteristics that are predicted by the present 



complete crossflow method and the small crossflow method. This is not an 



unexpected result because the Lucy Ashton is a fairly slender hull with 



very slowly changing cross-section shape along the length of the ship. 



Hence the values of the coefficient K„ are small everywhere along the hull 



and it is reasonable to expect fairly small boundary layer crossflow 



effects. The differences in the two sets of results shown in Figures 3 



through 6 are due mainly to the differences in the numerical integration 



method used by von Kerczek and the present method. This is indicated by 



the differences in the results on the keel, shown in Figures Ad and 5d, 



where the two methods solve identical equations. 



The second test calculation is of the boundary layer on the Swedish 



21 

 SSPA Model 720 double body. Figure 7, taken from Larsson's report, shows 



front and rear views of the streamlines along which measured and computed 



boundary layer properties were given. Larsson's calculation method starts 



from a momentum- integral-entrainment method closely related to the one 



described in this report. The main difference between these two boundary 



layer calculation methods is in the auxiliary data used for the crossflow 



velocity profiles and the numerical implementation of the methods. 



21 

 Larsson's method computes the boundary layer in the streamline surface 



30 



