Session: 34-04 Endwall, Seal & Leakage Flows II

Paper Number: 83551

83551 - Effects of Pure Shearing and Rigid-Body Rotation on the Evolution of Tip Leakage Vortex in an Axial Compressor Rotor 

Tip leakage vortex (TLV), which is primarily generated by the shear interaction between the leakage flow across the tip clearance and the main passage flow, has a large impact on compressor performance. In the current study, design and near stall condition of a rotor in a low-speed large-scale axial compressor are simulated based on delayed detached eddy simulation (DDES). Some commonly used vortex identification methods, including Q_cri, Q_M, λ_ci, Liutex, and recently developed local trace criterion (〖LT〗_cri), are applied and compared in capturing the vortex structures of TLV. The local fluid motion described by the velocity gradient tensor can be further decomposed into rigid-body rotation part, pure shearing part, and compressing-stretching part. Thus, the difference between vortex identifications and the kinematic characteristics of TLV are analyzed based on the decomposed components of fluid motion. Compared with the flow in the design condition, the shearing effect is stronger in the near stall condition. The TLV is enhanced but less stable, and the breakdown of it occurs earlier in the flow passage in the near stall condition.
The shear motion plays a significant role in the tip leakage flow, it always prevails over the rigid-body rotation except in the core of stable vortex, and causes the dissipation of the mechanical energy of fluid motion. Pure shearing is also the main reason for the varieties in the performances of different vortex identification methods in identifying the TLV. Some vortex criteria, such as Q_cri and λ_ci, are contaminated by shearing component along the principal rotation axis v_r, according to their analytical expressions, while the other components of shearing vector cannot be ignored. The predominance of shearing effect in some regions enables Q_cri and λ_ci to capture longer vortex trajectory and vortex tubes magnified diameter. However, Q_cri and λ_ci incorrectly identify the shear layer covers the blade suction side surface as strong vortical region, which can be avoided by Q_M and Liutex method, who accounts for the negative influence of the pure shearing and excludes the shearing contamination, respectively.
The 〖LT〗_cri-based elliptical region (LTER) indication method shows that the spiraling pattern of TLV changes during its evolution. The local spiraling trajectory of TLV stretches along the local rotation axis v_r with declination of the orbital radius in the swirling plane at its early stage, while it attenuates along v_r and the orbital radius amplifies after that. The breakdown of TLV happens accompanied with alternation of the spiraling pattern in space. And the spiraling pattern of TLV changes more dramatically in the near stall condition.

Presenting Author: Weibo Zhong Beihang University

Presenting Author Biography: Weibo Zhong is a PhD student in Research Institute of Aero-Engine, Beihang University (BUAA), China. His main research interests include the complex vortical flow in turbomachinery.

Authors:

Yangwei Liu Beihang University
Weibo Zhong Beihang University
Yumeng Tang Beihang University