Statistical structure and scaling behaviors of spanwise vorticity in smooth-wall turbulent boundary layers*

Within the canonical turbulent boundary layer the spanwise component of vorticity, $\omega_z$, is the only component that has a non-negligible mean value. For this and other reasons, the motions bearing $\omega_z$ play a central role in boundary layer dynamics. A compact four element (`Foss-style') hotwire probe was used to acquire well-resolved $\omega_z$ fluctuation time series over an unprecedented Reynolds number range, $1,500 \le \delta^+ = \delta u_{\tau}/\nu \le 15,000$. Very good spatial resolution ($\le 9$ viscous units) was maintained over the entire $\delta^+$ range by leveraging the low speed and large scale attributes of the HRNBLWT and FPF wind tunnels at Melbourne and New Hampshire, respectively. The present talk documents the behaviors of the statistical moments and frequency spectra of the $\omega_z$ fluctuations, and further explores the self-similarity between the mean and rms profiles seen at low Reynolds number. The observed $\omega_z$ behaviors are discussed relative to mean dynamical structure and the asymptotic properties of the boundary layer vorticity field.