A two-stage free-piston driver

The overall cost of free-piston driven facilities can be substantially redu ced if the contraction between the compression and shock tubes is replaced with a constant area section. However, with such an implementation, a new d river concept is required in order to achieve a realistic facility length. This paper describes a new free-piston driver type for expansion tubes whic h satisfies the above criteria. The technique is known as the two-stage fre e-piston driver where the driver gas is compressed in two distinct stages w ith a unique compound piston design. A new facility has been constructed (X -2) which is described in some detail. A quasi-one-dimensional numerical mo del of the compression process is also developed which agrees well with dri ver tube experimental results. This new driver is coupled to an expansion t ube arrangement where super-orbital test flows are generated. The results s how that a two-stage free-piston driver is capable of driving hypervelocity expansion tubes and therefore new facilities of increased sire but reduced cost are now possible.