Multi-component measurements in high Reynolds number turbulent boundary layers

Measurements, with highly resolved spectra are obtained in high Reynolds number ($Re_\tau$) turbulent boundary layers using sub-miniature cross-wires. The probe consists of $2.5 \mu$m diameter platinum wires welded across the sharpened stainless steel prong tips, contained in a volume of $0.4\times0.4\times0.2$mm$^3$. Velocity profiles are measured at various stream-wise positions with nominally matched unit Reynolds number ($U_\infty/\nu$). In this manner the same probe geometry affords approximately matched viscous-scaled sensor length ($l^+$) and sensor spacing ($\Delta s^+$) across the entire range of $Re_{\tau}$, such that Reynolds number trends can be observed free of spatial resolution effects. The probes have matched measurement volumes of approximately $14 \times 14 \times 7$ ($\pm 10\%$) viscous length scales across all $Re_\tau$. The prong is inclined at $10^\circ$ to the horizontal, permitting measurements close to the wall while also minimising blockage effects. The prongs are fabricated to account for this inclination, ensuring that the sensing elements remain parallel to the wall at the desired prong orientation. The resulting highly resolved multi-component velocity statistics up to $Re_\tau = 10,000$ and their associated trends against $Re_\tau$ will be presented.