Stability enhancement of a nine-stage axial compressor considering inter-stage matching and multi-stage casing treatment

This study investigates a multi-stage axial compressor characterized by high-mass-flow, wide operating conditions, and inter-stage bleed. Stability enhancement was conducted through hub modification and multi-stage casing treatment (CT) to achieve superior stall margin improvement (SMI) while maintaining inter-stage matching. Under conditions of 0.741 design rotational speed and 24% inter-stage bleed of the inlet mass flow, the critical instability regions are primarily concentrated at the tip sections of R4 and R8–R9. R4 is characterized by suction surface flow separation in the blade tip region, whereas R8-R9 exhibit strong TLF (Tip leakage flow)-mainstream interaction; both phenomena are highly likely precursors to tip-overload stall and tip-blockage stall respectively. Applying UMGCT (Uniform multi-groove casing treatment) to the R4 tip alone yielded an SMI of less than 1%, as the casing treatment altered inter-stage matching and shifted the instability location to the S4 root. This issue was effectively resolved by incorporating S4 hub modification, which increased the SMI to approximately 5%. To further enhance the SMI, two schemes—three-stage UMGCT (CT_R489) and two-stage UMGCT (CT_R48opt)—were validated based on the R4 UMGCT and S4 hub modification. The results demonstrate that with an optimized configuration of groove number and forward lean angle, the two-stage UMGCT can outperform the three-stage version, with the SMI of CT_R48opt exceeding 8%. The forward-leaned groove design enhances the axial momentum of the injected and aspirated flow at the rotor tip. By injecting positive axial momentum or aspirating flow with negative axial momentum, the UMGCT increases the axial momentum of the tip leakage flow and mitigates the low-speed blockage in the tip end-wall region. UMGCT scheme combined with both hub modification and multi-stage casing treatment achieves significant stability enhancement in multi-stage compressors.