Accelerated pump tube concept for hypersonic ground testing

This paper examines a new hypersonic wind tunnel concept which is referred to here as an ‘accelerated pump tube’ (APT). The facility can be considered a hybrid between a gun tunnel and an expansion tube. Like a gun tunnel, the test gas is isentropically compressed with a piston to raise its pressure and temperature; like an expansion tube, the compressed test gas is subject to an unsteady expansion to further increase its enthalpy and stagnation pressure. State-to-state analytical calculations incorporating high temperature equilibrium chemistry are presented which demonstrate that the APT is theoretically able to simulate a wide hypersonic terrestrial flight envelope from Mach 5–14, with significant capacity for pressure-length scaling. Potential practical benefits of this concept include relatively simple internal flow processes, removal of the need for a film secondary diaphragm and helium as a driver gas, and a reduction in experimental uncertainty through better defined internal boundary conditions and relatively low mechanical complexity. To assess the feasibility of the APT concept in a practical context, the paper considers how an APT based around a 25 m long, 600 mm diameter pump tube should be configured for a Mach 10 test flow. One-dimensional Lagrangian CFD analysis is used to compute piston dynamics for three different pump tube compression ratios and the associated test flows are characterised. The CFD results suggest that the concept should be viable in practice, and also validate the Mach 10 state-to-state calculations. • A new hypersonic wind tunnel concept is proposed, referred to as an ‘accelerated pump tube’ (APT). • The facility can be considered a hybrid between a gun tunnel and an expansion tube. • Detailed analysis shows that the APT can theoretically simulate a wide hypersonic flight envelope. • The facility promises to have lower complexity and simplified internal flow processes. • Benefits include lower operating pressures and no requirement for helium gas or film diaphragms.