Optimization of Self-Recirculating Casing Treatment for Centrifugal Compressors with Bent-Pipe Intake

Bent-pipe intake distortion restricts the stable flow range (SFR) and degrades the aerodynamic performance of centrifugal compressors. To expand the SFR while minimizing efficiency loss, this study carries out multi-objective optimization on a self-recirculating casing treatment (SRCT). Numerical simulations were performed at 65,000 rpm based on a four-factor, three-level orthogonal test design, focusing on four key geometric parameters: recirculation angle (α), downstream slot width (br), axial passage height (hb), and axial passage width (bb). The specific effects of these parameters on the SFR, isentropic efficiency (η), and a comprehensive stability index (ΔSFR/Δη) were systematically analyzed. Three optimal designs were obtained through this optimization approach, tailored to different operational requirements, namely CasingSFR, Casingη, and CasingOpt. The results indicate that the comprehensive optimal model (CasingOpt) achieves an optimal balance between SFR expansion and efficiency retention, extending the SFR by 28.67% with only a 10.84% reduction in isentropic efficiency. Flow field analysis further verifies that the optimized SRCT can effectively modulate tip leakage flow via low-energy fluid suction and reinjection, correct deviated inlet incidence, thereby mitigating the severe leading-edge flow separation and high-entropy generation induced by distorted inflow.