| Popis: |
Turbulent density fluctuations in the near wake (x/D 10) of a slender body were measured in a wind tunnel at M = 8. Autocorrelations were obtained at several stations as well as cross-correlations for various steamwise separations of the two measurement stations. In addition, power spectra and relative intensities of the fluctuations were measured. To obtain these data, the wake flow was seeded with a small fraction of sulfur dioxide, injected from the base of the model. A two-beam photometer, looking through the wake, was used to measure the fluctuations in the intensity of near-ultraviolet light, which is strongly absorbed by SO2. The signals from the two beams were combined in an analog correlator with a variable delay line. The resulting correlation functions were used to obtain time and space integral scales at various locations in the wake as well as the apparent convection velocity of turbulent eddies along the wake. Examination of these results showed that the observed density fluctuations are associated primarily with corrugations in the turbulent front defining the irregular wake edge. The results in general are consistent with the classic wake analysis for incompressible flows and with ballistic-range measurements of hypersonic wakes far downstream of spheres and cones. (Author) |
