  A study of the the main features of low- and high amplitude steady streamwise
wall transpiration applied to pipe flow is presented. The effect of the two
transpiration parameters, amplitude and wavenumber, on the flow have been
investigated by means of direct numerical simulation at a moderate turbulent
Reynolds number. The behaviour of the three identified mechanisms that act in
the flow: modification of Reynolds shear stress, steady streaming and
generation of non-zero mean streamwise gradients, have been linked to the
transpiration parameters. The observed trends have permitted the identification
of wall transpiration configurations able to reduce or increase the overall
flow rate in -36.1% and 19.3% respectively. A resolvent analysis has been
carried out to obtain a description of the reorganization of the flow
structures induced by the transpiration.
