Nowadays, the internal flow in aircraft engine compressors can be quite accurately reproduced at design condition by the CFD tools. However, CFD generally fails to simulate some singular 3D phenomena, near off-design conditions, such as the corner separation. Studies have pointed out that the separation regions are often over-estimated when the flow state is far from design condition, owing to the turbulence model. Much work is devoted to improving the capability of the turbulence model in capturing the onset and the extent of the corner separation, which is desired in the designing procedures.
In this paper, steady RANS simulations are carried out in the same configuration as an experiment of Ma et al. These simulations are obtained with a high-precision in-house Navier-Stokes solver (Turb’Flow). With the same mesh, an unsteady simulation (URANS) is subsequently presented, in order to investigate the influence of a fluctuating inflow.
Attention is focused on a specific angle of attack of 4 degrees, for which the three-dimensional corner separation is clearly observed. For the unsteady simulation, unsteadiness is imposed through perturbations of the angle of attack at the inlet. The results of the steady and unsteady computations are analyzed and compared with those of the experiment. The time-averaged URANS results agree well with the RANS results. The fluctuating inflow does not show much influence on the mean performance of the compressor cascade. The onset of the corner separation occurs earlier in the simulations than in the experiment, considering the blade surface pressure and the passage velocity profiles. However, the cross-stream extent of the corner separation appears slightly under-estimated by CFD, according to the outlet total pressure losses and the passage velocity profiles. Finally, the URANS simulation allows to recover bi-modal PDFs, as observed in the experiment.