This paper presents a numerical simulation of the unsteady flow in a transonic compressor stage. The simulations were performed using an unstructured mesh, 3D Navier-Stokes solver with a sliding interface between the mesh blocks containing the rotor and stator blades to permit a time-resolved calculation. The focus in the simulation is the endwall flow, its contrast with the mid-span flow and, in particular, the interaction of the rotor overtip leakage flow with the downstream stator.

The endwall region of both the rotors and the stators was predicted to be proportionally responsible for much more loss production than the mid-span sections of the blading. Unsteady effects were predicted to be responsible for rather more of the total loss production in the rotors than in the stators but the unsteady loss production in the rotors did not seem to be associated with the endwall flow but rather occurred over the bulk of the blade span caused by unsteady shock motion. By contrast, the rotor overtip leakage flow was shown to cause a considerable degradation of the stator performance near the casing. In the stators nearly a third of the loss production near the endwall was predicted to be directly due to unsteady effects associated with the rotor vortex interaction and a number of individual physical loss generating mechanisms were identified.

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