The Measurement of Radar-Plasma Signatures in a Hypersonic Shock Tunnel: Simulation and Experiment

The plasma sheath that forms around a body in hypersonic flight can change the radar signature substantially. The prediction of radar-plasma signatures, however, is complex, since it incorporates aerothermodynamics and electromagnetics and requires a number of critical assumptions on chemical and aerodynamic parameters as well as on the electromagnetic plasma model. Hence, such an approach requires thorough experimental validation to estimate and reduce its uncertainty. But radar data of hypersonic targets in free flight are extremely rare, and if existing, mostly unavailable. A different validation approach, which is common in aerothermodynamics, is to use short-time shock tunnel facilities, where for a few milliseconds, hypersonic flow conditions can be established. This article presents the adoption of this principle to the prediction of radar-plasma signatures. Under the hypersonic flow conditions inside a shock tunnel, a plasma sheath was generated above the surface of a spherical wind tunnel model and measured by an integrated experimental radar system. Afterwards, the plasma sheath and the radar signatures were simulated combining aerothermodynamic and electromagnetic solvers. Despite considerable uncertainties, good agreement between experiment and simulation was achieved.