Optimized Fillet Effects on the Loss Mechanism and Spatiotemporal Evolution of a Subsonic Compressor Cascade Using the SBES Model

A previous study demonstrated that the deliberate design of blade fillets with chordwise varying sizes improves the compressor performance better than the uniform fillet. An optimized variable fillet in a high-subsonic compressor cascade was numerically studied with a stress blended eddy simulation (SBES) model, a Reynolds-Averaged Navier-Stokes (RANS) and Large eddy simulation (LES) hybrid modeling method to elucidate further the flow mechanism of variable fillets and their influence on spatiotemporal evolution. The optimization of fillets at both design and off-design conditions is conducted using a parametric design method. The optimized variable fillet characterized by increasing and decreasing chordwise size can reduce the total pressure loss by up to 40% at the near stall condition without compromising performance at the design condition. According to the analysis of entropy and vortex transportation, total pressure loss reduction is attributed to viscous entropy generation rate and vorticity decreasing near the blade corner. The variable geometry enhances the spanwise pressure gradient and mitigates the transverse pressure gradient, inhibiting the horseshoe vortex and corner separation. A spatial-temporal evolution study indicates that the suction peak and corner flow regions exhibit periodic flow phenomena, with frequencies decreasing as the attack angle increases. The optimized variable fillet increases the periodic frequencies of the suction peak and corner flow while suppressing the corner flow region under near-stall conditions. The corner separation flow demonstrates a more pronounced periodicity and stability under the influence of the variable fillet. Further, the flow modal analysis utilizing the spectral proper orthogonal decomposition method reveals that corner separation and shedding wake are the primary sources of flow unsteadiness. The optimized variable fillet can increase the central modal frequency and significantly reduce the amplitude of unsteadiness under near-stall conditions.