Proposed Vertical Expansion Tunnel

It is proposed that the adverse effects from secondary diaphragmrupture in an expansion tunnelmaybe reducedor eliminated by orienting the tunnel vertically, matching the test gas pressure and the accelerator gas pressure, and initially separating the test gas from the accelerator gas by density stratification. This proposed configuration is termed the vertical expansion tunnel. Two benefits are 1) the removal of the diaphragm particulates in the test gas after its rupture, and2) the elimination of thewave system that is a result of a real secondarydiaphragmhaving a finite mass and thickness.An inviscid perfect-gas analysis andquasi-one-dimensionalEuler computations are performed to find the available effective reservoir conditions (pressure andmass specific enthalpy) and useful test time in a vertical expansion tunnel for comparison to a conventional expansion tunnel and a reflected-shock tunnel. The maximum effective reservoir conditions of the vertical expansion tunnel are higher than the reflected-shock tunnel but lower than the expansion tunnel. The useful test time in the vertical expansion tunnel is slightly longer than the expansion tunnel but shorter than the reflected-shock tunnel. If some sacrifice of the effective reservoir conditions can be made, the vertical expansion tunnel could be used in hypervelocity ground testing without the problems associated with secondary diaphragm rupture.