EFFECTS OF PURE SHEARING AND RIGID-BODY ROTATION ON THE EVOLUTION OF TIP LEAKAGE VORTEX IN AN AXIAL COMPRESSOR ROTOR

Tip leakage vortex (TLV) in an axial compressor has a considerable impact on aerodynamic performance. Hence, deeper insight should be gained into the evolution mechanism of the TLV. In this paper, the tip leakage flow (TLF) field of a low-speed large-scale axial compressor rotor at both design and near stall conditions by delayed detached eddy simulation (DDES) is analyzed. The swirling flow motion of the TLV is decomposed into three components: rigid-body rotation, pure shearing, and compressing-stretching. The effects of these swirling flow components on the evolution of TLV are investigated. Results show that the shearing and rotational motions of TLF at both design and near stall conditions vary because of the difference in leakage flow conditions. At the near stall condition, the TLV is stronger after its formation but breaks down earlier and changes more violently. Furthermore, the shearing effect plays a significant role in the TLF and prevails over the rigid-body rotation except in the core region of the stable vortex. Most of mechanical energy dissipation is caused by pure shearing. The spiraling pattern and orbital compactness of the TLV are investigated by the local trace criterion-based elliptical region (LTER) method. Results show that the main spiraling pattern of the TLV changes regularly as the TLV develops downstream. In addition, the decrease of the spiraling compactness level reflects the TLV breakdown due to the decrease of swirling strength caused by weaker rigid-body rotation and pure shearing. The swirling flow with high compactness caused by strong shearing effects contributes to the energy dissipation significantly.