SELECTION OF SHAPES 



For the first series of experiments, four models were selected. Since the purpose of this 

 series was to investigate the effects of Lg /D, only this parameter was varied. All the models 

 had rounded forebodies with prismatic coefficients equal to 0.667. The first forebody model 

 selected (4620-3) is designated as the parent model, L £ /D = 1.82; the resistance of this model 

 is then used as a baseline to assess the merits of the other forebodies. The remaining three 

 forebodies have L E /D ratios of 0.5, 1.0, and 3.0. The L £ /D = 0.5 forebody has a hemispher- 

 ical shape. The other three have Granville shapes and were derived from a common parent, 

 i.e., r = 0.8333 and kj = 10.0. Figure 2 shows the contours of the four forebody shapes. 



Of the five forebodies selected for experiment in Series 2, three had rounded shapes. 

 They were selected during a parametric investigation of forebody shape, using calculated 

 pressure distributions and transition locations for guidance. Pressures were computed for 

 several model shapes, using the Hess-Smith, potential-flow-computer program. 4 Boundary- 

 layer stability calculations were made for a few selected shapes at typical full-scale Reynolds 

 numbers, using the Smith-Gam beroni method. 5,6 Results were then compared with similar 

 calculations for the parent forebody shape, Model 4620-3. Shapes selected were chosen for 

 their persistence of laminar flow in the full-scale Reynolds number range. They were derived 

 from a common parent - r= 3.167, C p = 0.850, k { = 5.0 - having L £ /D ratios of 0.50, 1.00, 

 and 1.82. 



The first flat-faced forebody selected has a relatively small prismatic coefficient, 0.823, 

 and a forebody Lg/D of 1.216. The connecting curve between the flat face and the parallel 

 middle body on this model has an elliptical contour. In contrast, the second flat-faced fore- 

 body is extremely blunt with a prismatic coefficient equal to 0.933. A Granville two- 

 parameter cubic polynomial (k Q = 1.0, k 1 = 3.0) was used for the transition curve on this 

 model. The contours of the five forebodies of the second series are shown in Figure 3, and 

 the particulars of the nine models selected are given in Table 1 . 



Incipient cavitation speeds have been calculated for the nine forebody model shapes; all 

 are listed in Table 2. The model with the earliest predicted cavitation inception is 4620-7. 



Hess, J.L. and A.M.O. Smith, "Calculation of Potential Flow about Arbitrary Bodies, " Progress in 

 Aeronautical Sciences, Vol. 8, Pergamon Press, Inc., New York (1966). 



Smith, A.M.O. and N. Gamberoni, "Transition Pressure Gradient and Stability Theory, " Douglas Aircraft 

 Company Report ES-26388 (Aug 1956). 



Wazzan, A.R. et al., "Spatial and Temporal Stability Charts for the Flakner-Skan Boundary-Layer Profiles, ' 

 Douglas Aircraft Company, Report DAC-67086 (Sep 1968). 



