Turbulence structure in a boundary layer wind tunnel

Turbulence spectral analysis is a critical aspect of wind tunnel experiments. In this study, a modification of the Mann uniform shear model (M94), based on the Rapid Distortion theory (RDT), is proposed to adapt M94 for wind tunnel conditions and model the complete second-order turbulence structure. Firstly, the one-point spectra measured at heights ranging from 0.3 m to 1.5 m are analyzed. The total absolute error χ² for the modified M94 (M94-2) prediction is 0.998, compared to 1.6357 and 1.183 for M94 and the von Kármán spectral model, respectively; the results demonstrate the validity of the modification. Secondly, the spatial coherence is analyzed, with the spatial separations Δy and Δz ranging from 3.5 cm to 50 cm, M94-2 provides better predictions compared to the Krenk exponential coherence model. Notably, M94-2 is able to predict the turnaround of coherence at low wavenumber. Thirdly, the phase angle of the cross-spectrum for two vertically separated points is predicted by M94-2, M94-2 tends to overestimate the measurement due to noise contamination. In conclusion, the anisotropic spectrum of boundary layer wind tunnel turbulence can be modeled by M94-2 effectively with three parameters: αε²⁄³, L, and Γ, and the entire work is conducted within a unified theoretical framework.