Abstract
This paper studies the influence of tip clearance on the flow characteristics related to the performance. Based on full-passage numerical simulation with experimental validation, several clearance models are established and the performance curves are obtained. It is found that there exists an optimum clearance for the stable working range. By analyzing the flow field in tip region, the role of the tip leakage flow is illustrated. In the zero-clearance model, the separation and blockage along the suction side is the main reason for rotating stall. As the tip clearance is increased to the optimum value, the separation is suppressed by the tip leakage flow. However, with the continuing increasing of the tip clearance, the scale and strength of the tip clearance vortex is increased correspondingly. When the tip clearance is larger than the optimum value, the tip clearance vortex gradually dominates the flow field in the tip region, which can increase the unsteadiness in the tip region and trigger forward spillage in stall onset.
Highlights
It is the tip region of a rotor that is one of the most unstable regions in an axial compressor.For example, for the tip-critical rotors, the rotating stall was first observed in the tip region
This paper studies the influence of tip clearance on flow characteristics related to performance
The trend of performance change is discussed with the clearance increased from zero (0%τ) to large (2%τ), and the
Summary
It is the tip region of a rotor that is one of the most unstable regions in an axial compressor. As the experiment method and computational fluid dynamic method have been both highly improved, the flow structures and special phenomenon in the tip region were studied in detail, which included double leakage, vortex breakdown, self-induced flow, and active control technology, etc. For double leakage, it was first noticed by Khalsa et al [5] in the experiment and simulation results. As double leakage flow occurred in all working conditions with large tip clearance, vortex rope is generated near leading edge, which results in the high mixing loss and non-synchronous vibration. The flowfield characteristics under different tip clearances are compared, and the effects of the separation and the tip leakage flow on the efficiency and stability are discussed
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