The numerical investigation of circumferential groove casing treatment (CGCT) on a front 1.5 stage of a heavy duty gas turbine axial compressor was carried out to explore the connection between the stall inception type and the capacity of CGCT's extending the working range. Steady Reynolds-averaged Navier-Stokes (RANS) equations were solved by the in-house code NSAWET. Two representative sets of CGCT configurations were simulated at 90%, 100% and 110% of design rotational speed, corresponding to part-speed, full-speed and over-speed condition respectively. The process of the stall with smooth wall was revealed and analyzed by a steady state analogy method. Results showed that the effectiveness of CGCT was speed-dependent. The CGCT extended little operating range at the part-speed condition, however, with increase of the rotational speed, when the stall was incepted by breakdown of the blade tip leakage vortex (BTLV), CGCT improved stall margin by 2% approximately. Moreover, the study proposes that the mechanism of CGCT can be linked to the acceleration of the kinetic energy recovery process inside the BTLV core.
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