An expansion tube is a type of impulse facility

Impulse facility

A testing facility that relies on rapid release of stored energy to generate a short period of high enthalpy test conditions for testing of aerodynamic flow, aerodynamic heating and atmospheric reentry, combustion, chemical kinetics, ballistics, and other effects...

 that is conceptually similar to a shock tube

Shock tube

For the pyrotechnic initiator, see Shock tube detonatorThe shock tube is an instrument used to replicate and direct blast waves at a sensor or a model in order to simulate actual explosions and their effects, usually on a smaller scale...

 with a secondary diaphragm, an expansion section, a test section, and a dump tank where the endwall would be located in a shock tube. It is typically used to produce high enthalpy

Enthalpy

Enthalpy is a measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.Enthalpy is a...

 flows for high speed aerodynamic flow and aerodynamic heating and atmospheric reentry

Atmospheric reentry

Atmospheric entry is the movement of human-made or natural objects as they enter the atmosphere of a celestial body from outer space—in the case of Earth from an altitude above the Kármán Line,...

testing.