THE SUPERORBITAL EXPANSION TUBE CONCEPT, EXPERIMENT AND ANALYSIS

In response to the need for ground testing facilities for super orbita l re-entry research, a small scale facility has been set up at the Uni versity of Queensland to demonstrate the Superorbital Expansion Tube c oncept. This unique device is a free piston driven, triple diaphragm, impulse shock facility which uses the enthalpy multiplication mechanis m of the unsteady expansion process and the addition of a secondary sh ock driver to further heat the driver ps. The pilot facility has been operated to produce quasi-steady test flows in air with shock velociti es in excess of 13 km/s and with a usable test flow duration of the or der of 15 mus. An experimental condition produced in the facility with total enthalpy of 108 MJ/kg and a total pressure of 335 MPa is report ed. A simple analytical flow model which accounts for non-ideal ruptur e of the light tertiary diaphragm and the resulting entropy increase i n the test gas is discussed. It is shown that equilibrium calculations more accurately model the unsteady expansion process than calculation s assuming frozen chemistry. This is because the high enthalpy flows p roduced in the facility can only be achieved if the chemical energy st ored in the test flow during shock heating of the test gas is partiall y returned to the flow during the process of unsteady expansion. Measu rements of heat transfer rates to a flat plate demonstrate the usabili ty of the test flow for aerothertnodynamic testing and comparison of t hese rates with empirical calculations confirms the usable accuracy of the flow model.