Abstract
The tip leakage vortex (TLV) has aroused great concern for turbomachine performance, stability and noise generation as well as cavitation erosion. To better understand structures and dynamics of the TLV, large-eddy simulation (LES) is coupled with a homogeneous cavitation model to simulate the cavitation flow around a NACA0009 hydrofoil with a given clearance. The numerical results are validated by comparisons with experimental measurements. The results demonstrate that the present LES can well predict the mean behavior of the TLV. By visualizing the mean streamlines and mean streamwise vorticity, it shows that the TLV dominates the end-wall vortex structures, and that the generation and evolution of the other vortices are found to be closely related to the development of the TLV. In addition, as the TLV moves downstream, it undergoes an interesting progression, i.e., the vortex core radius keeps increasing and the axial velocity of vortex center experiences a conversion from jet-like profile to wake-like profile.
Highlights
The existence of clearance between impeller tip and casing wall in a turbomachine is inevitable for its operation
To check whether the large-eddy simulation (LES) is able to capture the accurate flow information and analyze the tip leakage vortex structures and dynamics characteristics, the present LES was validated against the experimental data
The qualitative comparison shows that the various cavitation patterns including the tip leakage vortex (TLV) cavitation, clearance cavitation and blade surface cavitation in the experiment are shown by the LES
Summary
The existence of clearance between impeller tip and casing wall in a turbomachine is inevitable for its operation This tip clearance is the major source of tip leakage flow, the production of complicated tip vortices, and turbulent flow. Lakshminarayana et al [7,8] used a triaxial hot-wire probe rotating with the rotor to determine the flow field and turbulence properties in the end-wall region of an axial compressor rotor. They found that the leakage flow starts beyond a quarter-chord and tends to roll up further away from the suction surface, and that all the components of turbulent intensities and stresses are high in the leakage flow mixing region. Clearance using surface flow visualization and a five-hole probe, and observed a multiple tip vortex structure (TLV, tip separation vortex, passage vortex and secondary vortex)
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