TURBULENT BOUNDARY LAYER WALL PRESSURE FLUCTUATIONS ON SMOOTH AND ROUGH WALLS.
MASSACHUSETTS INST OF TECH CAMBRIDGE ACOUSTICS AND VIBRATION LAB
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Turbulent boundary layer wall pressure measurements were made with pinhole microphones three times smaller relative to boundary layer thickness than microphones used in earlier work. The improved high frequency resolution permitted examination of the influence of high frequency eddies on smooth wall pressure statistics. It was found that the space-time decay rate is considerably higher than previously reported. Measurements of cross-spectral density made with 5 Hz band width filters disclosed low phase speeds at low frequency and small separation. Measurements were repeated on rough walls and parallels were drawn from knowledge of a smooth wall boundary layer structure to propose a structure for a rough wall boundary layer. The effect of independently varying roughness height and separation on the large and small scale turbulence structure was deduced from the measurements. It was found that roughness separation affected the very large scale structure, whereas the roughness height influenced the medium and very small scale turbulence. Author
- Fluid Mechanics