Shock‐Tube Performance at Low Initial Pressure

An electron beam densitometer has been used to investigate the behavior of a conventional 1⅛‐in. i.d. shock tube operating at initial pressures of the order of 1 mm Hg. These experiments show that such a shock tube does not perform as predicted by simple theory. Most of the experiments were performed in argon with shock Mach numbers ranging between 1.2 and 7.0. The most striking observation was that for a given shock velocity, Ms = 1.6, the distance between the shock wave and contact surface as observed at the densitometer was proportional to initial pressure and independent of expansion chamber length over a tenfold range of tube length. At an initial pressure of 0.5 mm Hg the time interval between the arrival of the shock and the contact surface varied between 600 μsec at Ms = 1.2 and 20 μsec at Ms = 7.0. The diaphragm pressure ratio (Ar ‐ Ar) required to produce a shock of velocity Ms = 1.6 varied from 200 at an initial pressure of 0.25 mm Hg to 20 at an initial pressure of 50 mm Hg. For a given diaphr...