Roughness effects on fully developed pipe flow at high Reynolds numbers

Well resolved turbulence measurments were conducted in the Princeton/ONR Superpipe throughout the smooth and transitional regime and into the fully rough regime. The pipe tested was a commercial steel pipe with $k_{rms}=5\mu$m. This pipe is smooth up to about $Re_D=800\times10^3$, and fully rough above about $Re_D=5\times10^6$. In order to resolve the turbulence at these high Reynolds numbers a nano-scale thermal anemometry probe (NSTAP) was used to obtain the data. This sensor has a sensing volume of $60 \times 2 \times 0.1 \mu$m which is one order of magnitude smaller than conventional techniques, allowing to study the effects of rougness independently of any spatial filtering effects at high Reynolds numbers. This new data reveals information about the behaviour of roughness both in the inner layer and the outer layer.