Case 1 is a simple test case because the wavelengths of the acoustic waves are relatively long. Hence, grid convergence can be achieved with a relatively coarse mesh. Also, the interblade phase angle is zero. This means that planar acoustic waves are formed in both far-fields and their direction of travel is parallel to the x-axis. In this case, one-dimensional non-reflecting boundary conditions are sufficient to ensure the non-reflection of the acoustic waves at the far-field boundaries. Note that there is an excellent agreement between the four methods for this case.