This paper analyses the flow in a transonic turbine stage, using numerical results from a full 3D Navier-Stokes computation over the whole stage. This analysis, based on the combination of time and space Fourier transforms, points out how a spatio-temporal periodicity phenomenon is involved in the so-called stator-rotor interaction.

A first comparison is made between the computational results using geometrical approximation and the results achieved by the complete simulation. This analysis points out how the signal is enforced by the numerical conditions at the circumferential boundaries.

The stator-rotor interaction produces low spatial harmonics which are identified as spinning modes by means of Fourier series. The analytical theory from Tyler and Sofrin (1962) is then used to define a general model of stator-rotor interaction. This model allows the determination of the angular speed of rotation of the spinning modes, and results are compared with the global numerical simulation.

Finally, a first analysis of the axial propagation of the spinning modes is proposed, and attention is focused on the fact, that only few parameters are necessary to reproduce the unsteady signal.

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