Turbulent flow and friction in a pipe with repeated rectangular ribs

Measurements were conducted in the fully developed turbulent flow in a pipe with internal diameter \(D\) at a Reynolds number of \({\text{Re}}_{{\text{D}}} = 1.6 \times 10^{5}\). The pipe walls were equipped with regularly spaced square ribs of relative height \(h/D = 0.154\), while the pitch-to-roughness height was varied between \(p/h = 1.67\) and \(p/h = 6.67\). The measurements include mean velocity components, Reynolds shear and normal stresses and pressure losses. It is investigated whether the effects of the large roughness on the (time and axially averaged) velocity profile can be described by the classical rough-wall formulation by allowing the value of the von Kármán constant to deviate from its standard value of 0.41.