An experimental and numerical investigation of a free-piston double-diaphragm shock tube is conducted. In shock tube flow sequence, shock speeds up to 12.7km/s are achieved in the low pressure tube for initial pressure 13.3Pa by using helium driver gas. The present paper is described especially on characteristics of the buffer tube. In the numerical simulation, the flow is modeled as unsteady, inviscid and compressible. The numerical method employs the Harten-Yee second order upwind TVD scheme. The influence of the primary and secondary diaphragm rupture process on flow characteristics is investigated in experiment and numerical simulation.
