Performance and Stall Margin Evaluation of Axial Slot Casing Treatment in a Transonic Multistage Compressor

Adverse pressure gradients are intrinsic to compressor flow behavior and are further intensified by secondary effects associated with rotor tip clearance flow interactions. Tip clearance generates leakage flow, which leads to the formation of tip leakage vortices, a major contributor to aerodynamic losses in axial compressors. These vortices significantly influence both compressor performance and operational stability. Extensive prior research has demonstrated that passive casing treatments, particularly axial slots, can substantially improve the stall margin in axial compressors. In this work, the performance of a new casing treatment geometry is investigated using the concept of recirculating flow within semi-circular axial slots. The proposed casing treatment geometry builds upon recent experimental findings involving single-rotor configurations. It was applied to the first rotor row of a three-and-a-half-stage (3.5-stage) axial compressor comprising an inlet guide vane followed by three rotor–stator stages. The numerical model incorporates axial slots with a novel periodic interface approach implemented in a multistage compressor simulation. Three-dimensional steady-state RANS (Reynolds Average Navier-Stokes) simulations were performed to investigate the aerodynamic effects of the casing treatment across various rotational speeds. The results for the casing treatment configuration were compared with those of a baseline smooth casing. The introduction of the new casing treatment produced noticeable modifications to the internal flow structure, particularly in the tip region, resulting in improved overall compressor stability within the operating range of 85 to 100% of design speed.