Sebastian Willems

Laminar to turbulent transition on the HIFiRE-1 cone at Mach 7 and high angle of attack

During the descent phase of the transition flight experiment HIFiRE-1 the angle of attack was higher than expected, since an anomaly occurred in the exoatmospheric pointing maneuver. All pre-flight ground tests were carried out at angles of attack below 6◦. Therefore several post-flight experiments at high angles of attack were performed in the hypersonic wind tunnel (H2K) of the German Aerospace Center in Cologne. The selected Mach number of 7 and the Reynolds number range cover the flow conditions of the flight phase which are relevant for the transition experiment. The test campaign included highfrequency surface pressure measurements with PCB R

HIFiRE-1 Boundary-Layer Transition: Ground Test Results and Stability Analysis

The HIFiRE-1 is a 7-degree half-angle circular cone with a 2.5-mm nose radius. A successful HIFiRE-1 flight experiment was carried out in March 2010. Due to an anomaly in the exoatmospheric pointing maneuver, the reentry angle of attack was higher than anticipated (5–15 degrees instead of near zero). A test campaign in the H2K hypersonic wind tunnel at DLR Cologne gathered high-frequency pressure fluctuation data and global heat flux via infrared (IR) thermography at the high angles of attack and Reynolds numbers encountered in the as-flown trajectory. This paper presents analysis of data collected at 0° angle of attack at freestream Reynolds numbers from 5.7 to 10.7e6 /m for 1.6- and 2.5-mm-radius nosetips. The transition onset and end locations derived from IR thermography coincide well with the earliest and largest amplification of pressure fluctuations identified by the fast-response surface-mounted pressure transducers. Stability analysis of the astested conditions was done with the Stability and Transition of Boundary Layers (STABL) software suite. An N-factor of 5.5 correlates well with transition location for the 1.6-mm radius nosetip. For the blunter nosetip, N ≈ 5.2 at transition. The peak pressure-fluctuation frequencies predicted by STABL agree within 8% of those measured.

HIFiRE-1 Surface Pressure Fluctuations from High Reynolds, High Angle Ground Test

The HIFiRE-1 is a 7-degree half-angle circular cone with a 2.5-mm nose radius. A successful HIFiRE-1 flight experiment was carried out in March 2010. Due to an anomaly in the exoatmospheric pointing maneuver, the reentry angle of attack was higher than anticipated (5–15 degrees instead of �0). A test campaign in the H2K hypersonic wind tunnel at DLR Cologne was mounted to gather high-frequency pressure fluctuation data and global heat flux via infrared thermography at the high angles of attack and Reynolds numbers encountered in the as-flown trajectory. This paper describes the analysis and interpretation of the surface pressure fluctuations; thermographic analysis is contained in a companion paper. Pressure-fluctuation power spectra were computed at azimuths from the windward to leeward rays in 45° increments at ten sensor locations along the ray, and the expected laminar, transitional, and turbulent regimes were encountered. The disturbances along the windward and leeward rays are presumed to arise from amplified second-mode waves. At 6° angle of attack, 250-kHz disturbances were detected along the 135°-from-windward ray; it is unclear whether these fluctuations arise from second-mode or crossflow instabilities. At 9° angle of attack, similar pressure fluctuations occur along the 135° ray prior to separation near the leeward ray.

Experiments on the Interaction of a Fast-Moving Shock with an Elastic Panel

Experiments on the interaction of a fast-moving oblique shock with an elastic panel in turbulent supersonic flow at Mach numbers of 3 and 4 were conducted to enhance the understanding of coupled flow–structure phenomena and for the validation of coupled simulations. A complex and challenging experimental setup allowed achieving remarkable shock motion, changing the impingement point within a few milliseconds, to excite high-amplitude oscillations of an elastic panel. The flowfield was analyzed by using high-speed pressure transducers and high-speed schlieren photography. The panel deflection was measured by nonintrusive high-speed capacitive and laser distance sensors. Measurements were also conducted on a rigid panel to be used as reference for the elastic case, and to allow a more detailed analysis of the shock-wave/boundary-layer interaction on the panel, yielding insights into the spatial and temporal distribution of frequencies occurring in the interaction area. Oscillations of the elastic panel with...