| Tip leakage flow has profound impacts on the performance and stability of compressors. And, the unsteady characteristics in tip region appear near stall conditions. To focus on the flow characteristics of rotor tip region and to study the originating mechanism of unsteady fluctuation at blade tip, three-dimensional steady and unsteady numerical simulation was conducted in the single passage and multi-passages’ internal flow field of a transonic axial compressor rotor.In order to investigate/study the effects of calculation methods on the results, the comparison of S-A model and DES model(Detached Eddy Simulation) is carried out in this paper. The result from unsteady simulation of rotor single passage show that, both S-A model and DES model can reflect overall unsteady flow characteristics of rotor tip region. And, both flow behaviors were showed that the dynamic balance between incoming main flow and tip leakage flow emerged, resulting in periodic oscillation of tip leakage flow. It is also showed that the swing of the leakage vortex immensely increases after the shock wave, which indicates the shock wave intensifies the unsteadiness of tip region.Rotor multi-passages simulation was carried out in this dissertation. And two inlet conditions were given to capture the rotating instability phenomenon in tip region. Results show that the inlet condition has important influence on the flow field structure of tip region. When inlet direction is non-axial, unsteady fluctuation also exists and single passage periodical form emerges at blade tip. That is to say, the flow behavior of each passage keeps uniform. While periodical form with several pitches in circumferential direction appears in tip flow field and an unsteady flow phenomenon like “rotating instability” spreading along circumferential direction occurs under axial inlet condition. Moreover, with the decrease of mass flow, the unsteady fluctuation enhances significantly and flow field structure changes in tip region. Furthermore, the tip leakage vortex breakdown is more grievous, which leads to more serious flow blockage and loss at blade tip. |
