Upgrade of the X3 super-orbital expansion tube

Expansion tubes are important facilities for the study of high enthalpy hypersonic flows which avoid the non-equilibrium chemical and thermal effects associated with the flow stagnation intrinsic to reflected shock tunnels. X3 is one of the largest freepiston super-orbital expansion tube in the world with an overall length of approximately 69 m and is capable of generating reentry speed flows equivalent to those experienced during a hyperbolic re-entry trajectory. It was originally built with a twostage free-piston driver to achieve the high compression ratio of a large diameter compression tube without the high construction costs of designing the large diameter tube to be strong enough to resist peak driver pressure loads. However, this arrangement proved difficult in operation. This paper describes the upgrades to X3, in respect to its physical layout. The facility has been recommissioned to incorporate a single-piston driver, a steady expansion nozzle and a new test section. Major changes have been made to the free-piston driver with a re-designed piston and launcher and a new end cap tube which is 200 mm thick to contain driver pressures up to 80 MPa. The re-designed piston introduces an area change at the primary diaphragm, ensuring that the maximum increase in total pressure and temperature can be gained as the driver gas undergoes unsteady expansion from sonic to supersonic conditions. The compression process steadily increases up to Mach 1 at the throat then gains of up to an order of magnitude in total temperature and pressure can be realised as the unsteady expansion process takes over. The area change will also increase test times; with a throat at the primary diaphragm, the piston mechanics can be more readily tuned to minimise reflection of waves off the piston which would otherwise reduce the test time. A new Mach 10 steady expansion nozzle has been developed which has increased the core flow and the test time for appropriate conditions. The dump tank has been replaced with a larger tank and test section giving a larger volume with greater potential for instrumentation.

[1]  C. G. Miller,et al.  Development and performance of the NASA Langley Research Center expansion tube/tunnel, a hypersonic-hypervelocity real-gas facility , 1984 .

[2]  John I. Erdos,et al.  Hypervelocity real gas capabilities of GASL's expansion tube (HYPULSE) facility , 1990 .

[3]  David Gildfind,et al.  Development of high total pressure scramjet flow conditions using the X2 expansion tube , 2012 .

[4]  Michael G Davey.  A Hypersonic Nozzle for the X3 Expansion Tube , 2006 .

[5]  A. Paull,et al.  Experiments on an expansion tube with a free piston driver , 1988 .

[6]  Matthew McGilvray,et al.  Scramjet testing at high enthalpies in expansion tube facilities , 2008 .

[7]  Madhat Abdel-Jawad.  Stability assessment of planetary entry vehicles in the X3 superorbital expansion tube , 2005 .

[8]  Matthew MacLean,et al.  High Enthalpy Studies of Capsule Heating in an Expansion Tunnel Facility , 2012 .

[9]  Michael Paul Scott.  Development and Modelling of Expansion Tubes , 2007 .

[10]  Bianca R. Capra,et al.  Impulse facilities for the simulation of hypersonic radiating flows , 2008 .

[11]  R. J. Stalker,et al.  A study of the free-piston shock tunnel. , 1967 .

[12]  Richard G. Morgan,et al.  A two-stage free-piston driver , 1999 .

[13]  R. G. Morgan,et al.  The Superorbital Expansion Tube concept, experiment and analysis , 1994, Aeronautical Journal.

[14]  Todd Silvester.  Multidimensional viscous flows at superorbital speeds , 2005 .

[15]  Richard G. Morgan,et al.  Free piston-Driven expansion tubes , 2001 .

[16]  Allan Paull,et al.  Test flow disturbances in an expansion tube , 1992, Journal of Fluid Mechanics.

[17]  Robert L. Trimpi,et al.  A Preliminary Theoretical Study of the Expansion Tube, a New Device for Producing High-Enthalpy Short-Duration Hypersonic Gas Flows , 1962 .