2 

 acoustic noise levels at 30.5 m/s were about 93 dB re 0.0002 dyn/cm 



(0.0002 Pa). These levels of ambient turbulence and acoustic noise were 

 considered low enough so as not to unfavorably affect the measurements of 

 boundary-layer characteristics. The maximum air speed which can be 

 achieved is 200 ft/sec (61 m/s); in the present experiments the wind tunnel 

 velocity was held constant at 150 ft/sec (45.72 m/s). 



An axisymmetric inflected (convex and concave) afterbody with a bow- 

 entrance length-to-diameter ratio (L^/D) of 2.05 was used for the present 

 experimental investigation. The detailed offsets are given in Table 1. 



Figure 1 shows a comparison of the present afterbody (Afterbody 5) and 



1 2 

 Afterbodies 1 and 2 previously investigated by Huang et al. The contour 



of Afterbody 5 changes from convex to concave at x/L = 0.913, whereas 



Afterbodies 1 and 2 are convex up to x/L = 0.96. Afterbody 5 is connected 



to a parallel middle body which is 6.0 ft (1.83 m) long and an existing 



streamlined forebody with a bow-entrance length-to-diameter ratio (L^/D) of 



1.82. The total model length is 9.55 ft (2.91 m) with a maximum forebody 



diameter of 0.917 ft (0.28 m) . 



The model was supported by two streamlined struts separated by one- 

 third of the model length. The upstream strut had a 15-cm chord and the 

 downstream strut a 3-cm chord. The disturbances generated by the support- 

 ing struts were within the region below the horizontal centerplane, there- 

 fore, all of the experimental data were taken above the model on the 

 vertical centerplane along the upper meridian where there was little effect 

 from the supporting struts. One-half of the model length protruded beyond 

 the closed-jet working section into the open-jet section. The ambient 

 static pressure coefficients across and along the entire open-jet chamber 

 (7.2 m X 7.2 m x 6.4 m) were found to vary less than 0.3 percent of the 

 dynamic pressure. Tunnel blockage and longitudinal pressure gradient 

 effects along the tunnel length were almost completely removed by testing 

 the afterbody in the open-jet section. 



The location of the boundary-layer transition from laminar to turbu- 

 lent flow was artificially induced by a 0.024 in. (0.61 mm) diameter trip 

 wire located at x/L = 0.05. Huang et al. found that the trip wire 



