Understanding unsteady flow phenomena in axial compressor often requires the use of time-accurate CFD simulations. In the present paper, the nonlinear harmonic method implemented in Fine/Turbo code has been used to examine and analyze the boundary layer transition and unsteady rotor-rotor interaction of the NWPU subsonic counter-rotating compressor. To validate the NLH simulation results, the predicted characteristics and spanwise distributions of aerodynamic parameters were compared with the measured data and rigorous full-annulus unsteady simulations at typical working conditions and a good agreement was achieved. Then, its ability to correctly capture rotor-rotor interactions is investigated in detail to advance the understanding of the flow physics involved. Based on the NLH method deterministic stresses have been post-processed to compare to the full-annulus simulation to analyze distinct sources of unsteadiness and their effect on the time-averaged flow field. The results show the good behavior of the NLH method and its ability to correctly predict global quantities as well as local flow physic. Closed spacing between rotors increasing the strength of potential perturbations and complexity of rotor-rotor interaction. The NLH method presents high precision on modeling deterministic stresses.

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