Theory of compressor stability enhancement using novel casing treatment, part I: Methodology

This paper proposes a novel casing treatment, designated a stall precursor-suppressed casing treatment. It is designedtosuppress stall precursorstorealize stall margin enhancementinturbomachinery. This paper first presents a physical and mathematical model to describe the casing treatment configuration as a wall boundary condition and then establishes the stability equation with its effect. The sensitivity of stall inception to different boundary conditions is considered numerically for both subsonic and transonic axial flow fan/compressors. One important finding from this numerical prediction and analysis is that such a casing treatment can be used to change stall inception even when using a casing treatment configuration with low open area ratio. Thus, a reduction of momentum loss due to recirculating flow can be realized, in comparison with a conventional recessed casing treatment with more than 50% open area ratio. It is thus theoretically possible to design an advanced casing treatment to affect the evolution of stall precursors and finally change stall inception without significantly changing the efficiencyof the fan and compressors.