Analysis on spike-type rotating stall in transonic axial compressor by dynamic mode decomposition

Abstract

The spike-type rotating stall in axial compressor is one of the major causes for the aeroengine failure. The evolution of the flow structures, especially in the rotor tip region, is very important to understand the mechanism and predict the onset of the rotating stall. However, with the limitation of the experimental technologies, the detailed flowfield during the stall was hard to be obtained. Not only that, the flow structures were not easy to be extracted from the results by the traditional numerical analysis method. In this paper, the detailed unsteady flowfields are obtained under the conditions from the near stall to the stable stall by the validated numerical simulation with a transonic axial compressor model. Then, the dynamic mode decomposition, as a novel method for the model reduction and decomposition, is verified and implemented to extract the flow structures from the flowfield of the spike-type rotating stall. It is found that the flow structures are well decomposed with their characteristic frequencies. By reconstructing the unsteady flowfields based on the selected modes, the effect and the evolution of the corresponding flow structure are clearly observed. From the near-stall to the stable stall, there are three types of flow structure that play important role in tip region. First, the structure of the tip clearance vortex shedding with blade passing frequency dominates the unsteadiness in the near-stall flowfield. Next, the structure of the vortex breakdown with the self-induced frequency provides the initial non-uniform disturbance for the spike generation, but it is soon eliminated with the strengthening of the stall cell. The third one is the stall-related structure, which is triggered by the spike disturbance and evolved to the stable stall cell. This kind of the developing process plays the dominant role on the unsteadiness of the stall.