Hypervelocity Expansion Tube (HET)
The Hypervelocity Expansion Tube (HET) facility is an impulse facility consisting of three sections: a driver, driven, and acceleration section, all with an inner diameter of 152 mm. In an expansion tube, the initial shock interacts with a contact surface, generating an unsteady expansion that further accelerates the test gas. Theoretically, a wide range of test conditions with decreased freestream dissociation can be achieved by varying initial pressures. In contrast, in a shock tunnel chemical and vibrational freezing commonly occur in the nozzle, and the Mach number of the test gas can only be varied by exchanging the nozzles. A range of test conditions up to Mach 7.1 with suitable core flow size have been experimentally verified in the HET through pitot pressure measurements, initial and transmitted shock wavespeed measurments, and the analysis of schlieren images of flow over simple geometries.