Design and characterization of the Sandia free-piston reflected shock tunnel

A new reflected shock tunnel capable of generating hypersonic environments at realistic flight enthalpies has been commissioned at Sandia. The tunnel uses an existing free-piston driver and shock tube coupled to a conical nozzle to accelerate the flow to approximately Mach 9. The facility design process is outlined and compared to other ground test facilities. A representative flight-enthalpy condition is designed using an in-house state-to-state solver and piston dynamics model and evaluated using quasi-1D modeling with the University of Queensland L1d code. This condition is demonstrated using canonical models and a calibration rake. A 25-cm core flow with 4.6-MJ/kg total enthalpy is achieved over an approximately 1-ms test time. The condition was refined using analysis and a heavier piston, leading to an increase in test time. A novel high-speed molecular tagging velocimetry method is applied using in situ nitric oxide to measure the freestream velocity of approximately 3016 m/s. Companion simulation data show good agreement in exit velocity, pitot pressure, and core flow size.