Self-sustained Shock Oscillations over Axisymmetric Bodies in Hypersonic Flow

The phenomenon of shock oscillations over conical bodies with a blunt axisymmetric base has been investigated experimentally at Mach 6. The experiments were carried out in the 0.5 m diameter enclosed free-jet hypersonic wind tunnel at IISc; this facility can achieve a unit Reynolds number of $9\times 10^{6}\,\,\mathrm{m}^{-1}$ at Mach 6. The axisymmetric test models consist of a base circular cylinder with a $25^\circ$ half-angle conical forebody that is 40 mm in length ($L$). The base diameter ($D$) was varied to obtain different $L/D$ ratios in the range 0.4 to 0.9 to study the effects of the geometric parameter on the oscillation dynamics. Time-resolved schlieren imagery from these experiments shows distinct ``pulsation'' and ``oscillation'' modes of shock oscillations, similar to previous observations from literature on spiked forebodies (the terminology for modes is borrowed from the same). The ``pulsation mode'' is seen at low $L/D$ ratios, and a switch to ``oscillation mode'' occurs above a $L/D$ ratio of 0.8. Detailed experimental results including an analysis of the different stages of shock oscillations will be presented at the meeting.