High Reynolds number rough-wall turbulent boundary layers

In his review of turbulent flows over rough-walls, Jimenez (2004) concludes that there are gaps in the current database of relevant experiments. The author calls for measurements in which $\delta/k$ and $k^+$ are both large---low blockage, fully-rough flow---and where $\delta/k$ is large and $k^+$ is small---low blockage, transitionally-rough flow---to help clarify ongoing questions regarding the physics of rough-wall-bounded flows. The present contribution details results from a large set of measurements carried out above sandpaper in the Melbourne Wind Tunnel. The campaign spans 45 rough-wall measurements using single and multiple-wire hot-wire anemometry sensors and particle image velocimetry. A floating element drag balance is employed to obtain the rough-wall skin friction force. The data span $20 < k_s^+ < 160$ and $30 < \delta/k_s < 200$ across a friction Reynolds number range of $2800 < Re_\tau < 30000$, targeting areas in the parameter space identified by Jimenez (2004) as being sparsely populated by pre-existing data. Smooth-wall data are also obtained across a similar Reynolds number range to enable comparison of smooth- and rough-wall structural features. Generally, the data indicate similarity in the outer-layer of smooth- and fully-rough wall-bounded flows.