Comparison of Ares I-X Wind-Tunnel-Derived Buffet Environment with Flight Data

The Ares I-X flight-test vehicle, launched in October 2009, carried with it 243 buffet-verification pressure sensors and was one of the most heavily instrumented launch-vehicle flight tests ever conducted. This flight test represented a unique opportunity for NASA and its partners to compare the wind-tunnel-derived buffet environment with that measured during the flight of Ares I-X. This paper discusses the comparison of these wind-tunnel-derived and flight-test-measured buffet environments, including fluctuating pressure coefficient and normalized sectional buffet-forcing-function root-mean-square magnitudes, frequency content of power-spectral-density functions, and force magnitudes of an alternating flow phenomena. Comparison of wind-tunnel-model and flight-test-vehicle buffet environments showed very good agreement with root-mean-square magnitudes of buffet-forcing functions at the majority of vehicle stations. Spectra proved a challenge to compare because of different wind-tunnel and flight-test conditions and data acquisition rates; however, meaningful and promising comparisons of buffet spectra are presented. Lastly, the buffet loads resulting from the transition of subsonic separated flow to supersonic attached flow were significantly overpredicted by wind-tunnel results.