Effect of non-uniform circumferential spallation of seal coating on the aerodynamic performance in a transonic axial rotor: A steady numerical simulation

Abstract

Seal coating is a critical component of a compressor, and its function is to minimize the blade tip clearance and prevent fluid leakage. Non-axisymmetric spallation of the seal coating can compromise its effectiveness and reduce the compressor's efficiency. In this study, a numerical simulation was performed on a transonic axial rotor to study the effect of non-axisymmetric spallation of seal coating on the aerodynamic performance. Circumferential deep grooves were used to represent the irregular peeling of the seal coating in the full-annulus grids CFD simulation. Results show that as the circumferential length of spallation of seal coating increases, the total pressure ratio and isentropic efficiency decrease, and the surge margin decreases at first but then increases. After seal coating spallation, the flow loss changes near the suction surface and the tip passage. The flow loss changes on the suction surface relate to the interaction between the leading-edge shock/passage shock and the boundary layer. At the tip passage, the tip leakage flow and secondary flow induced low-velocity region and the effect of spallation on blockage dominate the flow loss and instability. The change in surge margin is contributed to the amount of and the chordwise variation of tip leakage flow, and the surge margin drops to the minimum when the spallation length is 9 passages where a “double-twist” flow behavior of TLF occurs substantially.