Commissioning of the Oxford High Density Tunnel (HDT) for Boundary Layer Instability Measurements at Mach 7

Abstract

Experiments have been completed in the University of Oxford’s High Density Tunnel (HDT) to verify that it can be used for boundary layer stability measurements. These have replicated the research previously undertaken in the DLR H2K facility in 2013 using a sub-scale model of the HIFiRE-1 flight. This was a 7-degree half-angle axisymmetric cone with small nose bluntness. For the tests, the facility was operated in Ludwieg Tube mode with a contoured Mach 7 nozzle at a range of unit Reynolds numbers between 7.2 x 106 /m and 18.6 x 106 /m. Measurements with a Pitot rake at various axial locations showed excellent spatial and temporal uniformity with a core flow diameter of 280mm at nozzle exit, reducing to 200mm diameter at a downstream distance (from nozzle exit) of 420mm. Initial testing showed that an automated traverse mechanism could be used for the micro-alignment of the model to within 0.1 degrees in both pitch and yaw. Analysis of high-frequency surface pressure fluctuations at various azimuthal angles and angles of attack up to 12 degrees have shown good agreement with the H2K results, verifying that the HDT can be used for boundary layer instability measurements.