Numerical Analysis of Fluid Dynamics of Tip Leakage Vortex with Different Gap Widths in an Axial Flow Pump

摘要

The effects of different tip clearance widths (including 0.15mm, 0.45mm,1.2mm) on the tip leakage vortex dynamics and related influences of main flow characteristics of an axial flow pump are investigated. The performance of the model pump obtained by simulation shows good agreement with experimental data. The flow structure in the tip region is analyzed by computing the distribution of vorticity, mean axial velocity and turbulent kinetic energy (TKE). In depicting the features of vortex core, the swirling strength method is adopted. Through comparison for the same tip clearance, it is concluded that axial velocity of leakage flow at X = 0.5 (a plane relative to blade) decelerates while axial velocity of mainstream flow increases as the flow rate increases. Distributions of TKE in the tip gap also have similar trends at different flow rates and tip widths, that is first increasing to a maximum value where tip separation vortex (TSV) occurs then decreasing close to zero near casing wall. Based on the analysis of the axial velocity and TKE contours, the mainstream most cannot go through tip clearance for 0.15mm tip and tip separation vortex only happens at the corner of blade pressure side. While for 1.2mm tip, tip separation vortex also appears in the tip clearance, connecting with shear layer and interacting with tip leakage vortex close to blade suction side, finally result in high intensity of vortex and entrained by tip leakage vortex (TLV). Additionally, the vortex core's vorticity along TLV trajectory reduces while the pressure increases for all tip widths, indicating cavitation would be prone to generate around the leading edge. Besides, the vorticity of the vortex core for the same flow rate increases at the same location when the tip width increases from 0.15mm to 1.2mm. The roll-up process of TLV is three-dimensional and different vorticity layer exist in the tip region that could feed the turbulence into TLV. As for different flow rates and tip widths the process is similar while the value differs greatly.