The acoustic properties of a perforated plate are known to be dependent on, amongst other factors, the external flow. An ongoing scientific discussion is regarding the boundary condition of the perforated liners for acoustic propagation with different directions relative to the mean flow. This is due to the combination of these conditions resulting in varying acoustic properties of perforates, when evaluated by different impedance eduction measurement techniques. The work presented here is to contribute to the research and provide results for the acoustic behaviour of perforates under different flow conditions. A majority of the test rigs used to determine the acoustic impedance consider either upstream or downstream acoustic propagation in a two-port configuration. Here, a three-port measurement technique is used to observe the transfer impedance of the perforate using excitation from all the three directions. This setup allows for studying the effect of flow under grazing as well as normal acoustic incidence. Validation of the experimental results as well as comparison with existing analytical models to determine the transfer impedance of perforates are presented.