Abstract

The leakage flow that is developed between the rotor and the casing of an axial compressor is usually associated with losses and can promote the arising of rotating stall. During its life, an axial compressor can be subject to a variation of the tip clearance due to the aging of the machine, which can modify the leakage flow and affect its performance. The prediction of the tip leakage flow and of its evolution with gap size is thus essential to estimate correctly the performance and operability of a compressor stage. The support of this study is a single stage compressor for which three different gap size ratios R=τc=3.4%, defined by the tip gap size τ over the axial chord c) are considered (R = 0.6 %, 1.2 %, 2.4 %). Reynolds Averaged Navier-Stokes (RANS) simulations are performed on the three configurations. The analysis is performed with two types of computational domains (a single blade-channel and one tenth of the full annulus geometry). The aim is to identify the configuration which provides reliable results at the most reasonable computational cost. Then, a numerical study on the effect of the tip gap size on the performance and flow topology of the compressor is conducted, especially at near stall operating conditions.

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