The Study Of Compressor Tip Clearance Flow Structure

The compressor tip leakage flow is between the rotor blade tip and the casing. There is fluid leakage flow through the clearance. Tip leakage flow is an important part of varies of flow in the compressor. It is also the important part of loss in the compressor. The flow of a rotor blade tip clearance not only increases the load near tip clearance, reduces the compressor efficiency, but also blocks the cascade passage, and even causes surge seriously, reduces the compressor stable working range. So it has great significance of the flow structure investigation of compressor blade tip clearance.This article based on the compressor airfoil NACA64-A905 to establish the three-dimensional numerical model. It discusses the effect of different tip clearance gap sizes on the compressor blade field. It calculats different sizes of the tip clearance flow field that clearance sizes are 0.5%c( c is the blade chord), 1%c and 2%c. Simulating the flow structure of compressor cascade that clearance sizes are 2%c and the stall incidences varies from-2° to 30°. It makes the unsteady numerical calculation to the compressor moving blade tip leakage flow. Spectrum relationship of clearance flow is taken by FFT processing. Finally it makes the mode analysis on velocity field of the compressor cascade export section through Dynamical Mode Decomposition(DMD).The result shows that the tip leakage vortex intensity is enhancing with the increase of the leakage size. Loss of the compressor field is increasing. Separation state of boundary layer is different when the blade is in a post-stall condition. Because the leakage vortex can resist the boundary layer separation of blade tip region, and the passage vortex can promote the boundary layer separation of blade root region. Separation decreases along the blade height. And the blade root separation is obvious with the incidence increasing. The leakage vortex shedding frequency is 1818 Hz and the leakage vortex shedding shows the periodic unsteady. We get the appropriate modes to different eigenvalues through Dynamical Mode Decomposition. The zero-order mode represents a steady- state spatial structure of the vortex. The first-order mode represents a spatial structure of turbulent vortex. The second-order mode represents the spatial structure of two turbulent and interactive vortexes. Three corresponding modes of DMD are correspond to the first three frequencies of FFT.