Numerical study of the unsteady behaviors and rotating stall inception process in a counter-rotating axial compressor

Abstract

Unsteady computations of a counter-rotating axial compressor are performed and analyzed to investigate the unsteady behaviors in the compressor and the role of the tip leakage flow together with the rotating stall inception process. The results show that the oscillation on the pressure side is much stronger than that on the suction surface for both rotors, especially near the tip region where the trajectory of the tip leakage vortex (TLV) interacts with the blades most often. There exists a periodical leading edge spillage of the interface in rotor2 due to the unsteadiness of tip leakage flow (TLF) at near-stall condition. The blockage generated by the TLV increases dramatically due to the increasing strength of the TLV and the backflow phenomenon as the mass flow decreased. The appearance of the frequency components of 0.5 blade passing frequency (BPF) and 1.5BPF from 0.64BPF can be viewed as the rotating stall inception warning. The fluctuation strength of oscillation frequencies of 0.5BPF and 1.5BPF decreases rapidly from leading edge to trailing edge in rotor2, which indicates that the unsteady fluctuation of TLF at the leading edge in rotor2 is responsible for the stall inception of the compressor. Additionally, both the leading edge spillage and trailing edge backflow phenomena are observed for spike initiated rotating stall at stall point.

Numerical Investigation for the Impact of Single Groove on the Stall Margin Improvement and the Unsteadiness of Tip Leakage Flow in a Counter-Rotating Axial Flow Compressor

“…Past research on this compressor has indicated that the TLF from near the mid-chord plays a more important role in the generation of the self-induced unsteadiness of the TLF [37,38]. In the current paper, the result shows that it is more effective to improve the flow stability by controlling the critical TLF released from near the mid-chord.…”

“…For example, a circumferential groove with its leading edge positioned at 20% tip axial chord length downstream of the blade leading edge is named G2. Previous research on this compressor has indicated that the flow fields in the tip region of R2 are responsible for the spike-type flow instability of the CRAC [35,37,38]. Therefore, different circumferential single grooves over the blade tip of R2 were numerically investigated in the current paper.…”

“…Endeavors to gain further insights into the flow physics in CRAC have been conducted on the important factors, including axial spacing between two rotors, unsteady effects, inlet distortion, etc. [30][31][32][33][34][35][36][37][38]. Compared with a conventional compressor stage, it was found that there are many new characteristics and unique flow phenomena in CRAC.…”

Effects of tip clearance size on the unsteady flow behaviors and performance in a counter-rotating axial flow compressor

“…In addition, previous researches showed that the flow field in the tip region of R2 is responsible for the spike-type flow instability of the CRAC. 26,29 Therefore, the impact of TLF from R1 becomes more and more significant due to the increase of TCS, which plays an important role in the deterioration of the performance of both R2 and the counter-rotating stage because of the rotor–rotor interaction effect. The analysis above shows that there are two aspects of influence from the increase of TCS.…”

“…It has been found that there are many fresh characteristics and unique flow phenomena in CRAC compared with the conventional compressors. 22–29…”