DYNAMIC CHARACTERISTICS OF THE TIP CLEARANCE FLOW BASED ON THE LEAKAGE FLOW MODEL

Leakage flow in the tip region significantly affects the turbomachinery performance, such as the efficiency, aerodynamic stability and noise. An accurate and in-depth understanding of the dynamic characteristics of leakage flow is the premise of the flow mechanism analysis and flow control. A simplified three-dimensional multi-wall leakage flow model was employed, which characterizes the unique geometric feature of multiple walls with a tip narrow gap and aerodynamic characteristics, i.e., the shear layer between confined jet and mainstream and the tip leakage vortex (TLV). Subsequently, the wall-adapt local eddy-viscosity large-eddy (WALE LES) simulation was used for the simulation. Based on the Liutex and Spectral proper orthogonal decomposition (SPOD) method, the flow structure, main fluctuation structure and unsteady source of the leakage flow were studied. The results shows that there are TLV, secondary tip leakage vortex (STLV) and induced vortex (IV) in the tip field driven only by the leakage flow. The main fluctuation contains the shake of the TLV’s core, breakdown of the IV and generation of the STLV. Furthermore, the STLV has a crucial influence on the development of the vortex structure and unsteady characteristic of the tip field. Kelvin–Helmholtz instability induced by the strong shear layer under the influence of small disturbances is at the bottom of the explosion. However, this cannot be resolved by the Reynolds-averaged Navier-Stokes (RANS) method.