The impact of variable fillets on corner separation in a liner compressor cascade

Abstract

The performance of highly-loaded compressor is retricted by complex three-dimensional corner separation. The fillet with variable geometry around the blade has shown its potential in reducing the corner separation. However, there are no specific design criteria for fillets. Additionally, the impact of variable fillets on flow mechanisms and unsteady flow phenomena remains unclear. In this paper, the NACA65-K48 cascade profile without a fillet is used as a baseline. A parametric design method is developed to generate fillets with uniform and variable profiles along the axial direction. Cascades with two uniform and three variable fillets are profiled to explore the effect and flow mechanisms of fillet sizes. Steady numerical simulations are carried out in these cascades at different attack angle conditions. Compared with uniform fillets, all three variable fillets are able to improve performance at near-stall point without degradation at other attack angles. The fillet with size increasing and gradually decreasing along the chord has the best performance improvement within the full attack angle range. Analysis of axial and spanwise wall shears indicates that uniform fillets lift the separation area upward as a whole, while variable fillets eliminate small endwall separation and significantly reduce large-scale corner separation to decrease losses over the entire operating range. To further elaborate the key flow and loss mechanisms, unsteady simulations are conducted with the Stress Blended Eddy Simulation (SBES) model. SBES simulations predict near stall conditions comparable to steady results. The results demonstrate that variable fillets reduce corner separation by smoothing transition between blade and endwall and reducing transverse pressure gradient. The configuration with increasing then decreasing fillet size shows the greatest potential for improving performance, by suppressing additional trailing edge separation caused by large fillet size.