Afterbody Pressure Correlations for Vehicles with Ablated Nose Shapes

Abstract

ACORRELATION method is presented for determining the afterbody pressure distributions over the conical afterbodies of slender re-entry vehicles at small angles of attack that have been severely ablated or eroded in the nosetip region. The technique utilizes flowfield solutions for the pressure distributions over symmetrical sphere-cone re-entry vehicles at zero angle of attack. The method is shown to reduce the afterbody pressure data obtained using seven distinctly different nosetip configurations to a single correlation curve. Contents A comprehensive wind tunnel test program to obtain pressure distribution data was conducted at M^ = 8 in tunnel B at the Arnold Engineering Test Center, Arnold Air Force Station, Tenn. The baseline sphere-cone model which was tested was a 6.7-deg half-angle conical afterbody with a bluntness ratio (RN/RB) of 0.227. The seven nose configurations shown in Fig. 1 were tested and the nose attachment plane was located at body station X/L = 0.173. The pressure data from the present experiments were correlated using the axial distance parameter (CPc /^Tc~A N . XS/DN) suggested by Mirels and Thornton1 and a pressure parameter, CP/CP where CP is the sharp cone pressure, DN is the diameter of the nose, CAN is the nose axial force coefficient referenced to the nose base area, and Xs is the axial distance from the nosetip sonic point. The experimental pressure data for each of the ablated nosetips is correlated against the spherical nosetip data in Fig. 2, using the modified distance parameter. The pressure parameter was not utilized in this exercise since experimental data were available for only one cone angle. It can be seen from the plot that the axial distance correlation parameter has quite effectively collapsed the afterbody pressure data that were obtained with rather diverse nose shapes to the correlation curve obtained for the spherical nose. The pressures in the region less than one nose diameter from the nosetip are not well correlated. The experimental results previously presented clearly indicate that reasonable afterbody pressure distributions for vehicles with severely ablated nosetips can be obtained from sphere-cone pressure distributions. The a = 0 pressure distribution along the length of a spherecone re-entry vehicle with a cone half-angle of 6.7 deg was calculated for M00=8, using the Rakich2 method of characteristics solution, out to a distance of 160 nose radii