where there was no 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 mx 7.2 mx 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 turbulent 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 effectively moved the location of the 



virtual origin to x/L = 0.015 for axisymmetric models at a length Reynolds number 



f\ ft 



of 5.9 X 10 . The virtual origin for the turbulent flow is defined such that the 



sum of the laminar frictional drag from the nose to the trip wire, the parasitic 



drag of the trip wire, and the turbulent frictional drag aft of the trip wire is 



equal to the sum of the laminar frictional drag from the nose to the virtual origin 



and the turbulent frictional drag from the virtual origin to the after end of the 



model. The virtual origin locations for the three-dimensional body are expected to 



be different for different streamlines. Due to the limited number of grid locations 



2 

 used in the present calculation, the location of the transition for the C K boundary- 

 layer calculation is set at a constant value of x/L = 0.030. The computed differ- 



1 2 

 ences in velocities using x/L = 0.01 and x/L = 0.03, for axisymmetric body 1, ' 



are found to be less than 0. 1 percent of the free-stream velocities in the tail 



region. Thus, the error of using the constant transition location of x/L = 0.03 



2 

 for the present C K computation is expected to be negligible. 



INSTRUMENTATION 

 A series of 0.031-in. (0.8-mm) diameter pressure taps were embedded normal to 

 the surface of the stern at nine x/L locations. When the model was rotated about 

 its axis, the pressure taps were at the upper meridian location. Additional taps 

 were added for model alinement; see Figures 3 and 4. The model was alined by 

 balancing the surface static pressure about a line of symmetry. From Figure 3, the 

 model is alined when symmetrically located pressure taps at c and d, and at e and f, 

 give equal pressures, i.e., p (c) = p (d) , p (e) = p (f ) . The model was rotated to 



