Measurements of Sub-Convective Pressure Fluctuations in Turbulent Boundary Layers Across Various Facilities

Measurements of the wall-pressure wavenumber-frequency spectrum beneath a turbulent boundary layer are of great importance for understanding how many vehicles and structures of interest radiate noise when exposed to a moving fluid. Of particular interest are the sub-convective pressure fluctuations, which are both critically important vibro-acoustically, but present a difficult challenge to measure accurately. Modeling the wall-pressure wavenumber-frequency spectrum requires high-fidelity measurements, which have been achieved through the use of a novel array of linearly separated sub-resonant sensors. This work investigates how different facilities impact the measurement of the wall-pressure wavenumber-frequency spectrum beneath smooth wall turbulent boundary layer, with a special focus on the sub-convective pressures. Measurements have been be taken in two facilities: the Stability Wind Tunnel and Virginia Tech and the Boundary Layer Wind Tunnel at the Naval Surface Warfare Center Carderock Division. Measurements are taken at a single similar condition, allowing for direct comparisons of the wall-pressure auto-spectral density, cross-spectral density, and wavenumber-frequency spectra. Results are also compared to the Chase and modified Corcos models of the wavenumber-frequency spectra to assess accuracy and to determine whether the facility has a significant impact on model agreement. Results indicate that across facilities, a linear array of sub-resonant sensors measures a similar wall-pressure wavenumber-frequency spectrum which agrees most closely with the Chase model in the sub-convective regime. Isolation of the measurement system from background noise is favorable but not necessary for reasonable measurements of the wavenumber-frequency spectrum, but heavily impacts the measurements of the auto-spectral and cross-spectral density.