A major discussion in the scientific community is the effect of the acoustic propagation direction being relative to the mean flow direction on the acoustic boundary condition posed by perforated liners. The reason being that the results from liner-impedance-eduction measurements show acoustic propagation upstream or downstream to the flow direction giving different resulting acoustical impedances. This paper contributes to this continuing effort to gain confidence in results obtained under different acoustical excitation and flow configurations. Instead of a traditional two-port configuration, by placing a perforate sample in a T-junction, this paper presents a three-port measurement technique. The transfer impedance of the perforate is determined under grazing as well as under normal incidence. Moreover, to study the effect of acoustic incidence relative to the flow directions, transfer impedance is also determined under the presence of grazing flow. A comparison of the measurement results with existing analytical and semi empirical models is also presented. An attempt to determine the nature of the transfer impedance under normal acoustic incidence is carried out and an analogous behavior between an empty T-junction and the perforated sample is proposed.