Effects of boattailing on the turbulence structure of a compressible base flow

The large-scale turbulent structures in the near wake of a bottailed, axisymmetric afterbody immersed in a supersonic flow are examined using aplanar Mie/Rayleigh scattering visualization technique. Seven key regions in the near wake are studied in both side- and end-view orientations. Estimates of the mean structure size, shape, and inclination are made using spatial correlation analysis, and the effects of the turbulent structures’ passage are measured via steadiness and convolution analysis techniques. The results indicate that base drag is decreased by afterbody boattailing because the turbulent structures are generally less active in the separated flow region, and, as a result, shear-layer growth is suppressed. The latter result occurs because the large-scale turbulent structures are further inclined down toward the mean flow direction and tend to be organized more in the streamwise than in the spanwise direction near the base.