Tip Flow Unsteadiness and Blade Row Interactions for a Low-Speed Compressor Rotor

A numerical investigation has been conducted to determine the effects of self-excited tip-leakage flow unsteadiness, upstream stator wakes, and downstream blade row interactions on the performance prediction of a low-speed research compressor rotor. Calculations included a single blade row rotor configuration as well as two multiblade row configurations: one in which the rotor was modeled with an upstream stator and a second in which the rotor was modeled with a downstream stator. Steady-state and time accurate calculations were performed using a Reynolds averaged Navier-Stokes solver, and the results were compared with detailed experimental data at operating conditions corresponding to the compressor design point, near stall, and a midpoint between the two. Differences in the performance predictions between the three configurations were then used to determine the effect of the upstream stator wakes and the downstream blade row interactions. Results obtained show that for this compressor with rather large tip clearance time accurate calculations are a vast improvement over steady-state calculations, but the upstream stator wakes and the downstream blade row interactions have only a small effect on the numerical solution. In this paper, changes in the rotor flowfield due to the upstream and downstream stators are investigated and discussed to explain the limited impact of the stator wakes and downstream blade row interactions on this tip dominated flow. In addition, the unsteady nature of the rotor tip vortex at near stall conditions is discussed to explain the improvement of time accurate analysis over steady-state computations.