Free Piston Shock Tunnels HEG, HIEST, T4 and T5

In hypervelocity flows the speed of the considered fluid is much larger than the speed of sound. Commonly the hypersonic flow regime is considered to start above a Mach number, M, of 5. Ground based testing of such flows is performed in many different types of facilities. The reason for this is the large range of flow conditions and phenomena encountered in hypersonic flight and the fact that no single facility can simulate all relevant flow parameters simultaneously. Therefore, in hypersonic testing, partial simulation of different flow phenomena is performed in different types of facilities. Examples are Mach-Reynolds number simulation in cold hypersonic ground based test facilities, verification and qualification of hot structures of space vehicles in arc–heated test facilities or the investigation of the influence of the chemically reacting flow past an entry or re-entry vehicle on its aerodynamic behaviour in shock tunnels or shock expansion tunnels. In the present article, the operating principle of free piston driven shock tunnels is presented and examples of research in the worldwide largest facilities is discussed