4.1. Validation cases
The GIT test section, illustrated in Fig. 2, was 0.8128 m long and had a square cross-section with an internal width and height of 0.0508 m. It contained an axially centred liner with a length of 0.4064 m, which formed the centre of the upper wall.
The remaining walls were rigid. Acoustic waves in the plane-wave range were generated on the upstream side and a near anechoic termination is downstream. The tube exit impedances from Ref. [11] are given in Table 1. Two flow conditions are considered here – firstly, with no mean flow (M ¼ 0:0) and, secondly, with a mean flow of average axial Mach number M ¼ 0:335. Acoustic pressure measurements x (1) in the discretisationscheme. Therefore, this boundary condition were made at thirty-one points along the lower surface of the GIT (opposite the liner)