Evolution of the flow instabilities in an axial compressor rotor with large tip clearance: An experimental and URANS study

With modern engine designs trending toward smaller cores to increase propulsive efficiency, the gapto-span ratio in compressors is expected to increase, especially for the rear stages. Detailed knowledge of stronger tip clearance flow and its impact on compressor instability under large clearance condition become increasingly important. The present study is aiming for illuminating the instability evolution and the underlying flow physics in a large-tip-gap compressor, with the use of casing-mounted pressure transducers to acquire the unsteady nature of tip flow, and full-annulus URANS to obtain the three-dimensional flow details related to instability generation. Results show that flow instability evolution of the compressor along speed-line experiences three stages: stable state, rotating instability, and rotating stall. Two critical behaviors of tip leakage vortex (TLV) are found to relate to the transition of instability pattern. As TLV moves to the adjacent blade trailing edge, it starts to oscillate under the interaction with the adjacent blade, leading to a short-length rotating disturbance, i.e. rotating instability. At near-stall condition, as the interface of TLV and main-flow exceeds the passage inlet plane, forward spillage occurs along with radial vortexes periodically shed from blade leading edge. The periodically generation, movement and decay of leading edge vortexes (LEVs) constitute an orderly propagating disturbance rather than evolve into a stall cell. However, as the compressor is further throttled, the orderly propagation of LEVs collapses due to their scattering, resulting in the generation of stall cells with local stronger blockage and higher entropy. (C) 2019 Elsevier Masson SAS. All rights reserved.