Based on a novel control scheme, where a steady modification of the
streamwise velocity profile leads to complete relaminarization of initially
fully turbulent pipe flow, we investigate the applicability and usefulness of
custom-shaped honeycombs for such control. The custom-shaped honeycombs are
used as stationary flow management devices which generate specific
modifications of the streamwise velocity profile. Stereoscopic particle image
velocimetry and pressure drop measurements are used to investigate and capture
the development of the relaminarizing flow downstream these devices. We compare
the performance of straight (constant length across the radius of the pipe)
honeycombs with custom-shaped ones (variable length across the radius). An
attempt is made to find the optimal shape for maximal relaminarization at
minimal pressure loss. The maximum attainable Reynolds number for total
relaminarization is found to be of the order of 10.000. Consequently the
respective reduction in skin friction downstream of the device is almost by a
factor of 5. The break-even point, where the additional pressure drop caused by
the device is balanced by the savings due to relaminarization and a net gain is
obtained, corresponds to a downstream stretch of distances as low as approx.\
100 pipe diameters of laminar flow
