Numerical investigation of the unsteady flow behaviors in a counter-rotating axial compressor

Abstract

Unsteady numerical simulations of a counter-rotating axial compressor are performed to investigate the unsteady effects of rotor-rotor interaction process and the tip flow unsteady behavior near the stall operating condition. The results show that potential effects from the rear rotor have a more pronounced influence on the front rotor. Because of the interaction between the two rotors and the unsteady flow behaviors, the strongest fluctuant regions are different for the two rotors. Additionally, the oscillation on the pressure side is generally much stronger than that on the suction side. Frequency analyses show that self-unsteadiness occurs with the frequency of 0.76 blade passing frequency due to the impingement of the tip leakage flow on the pressure side near leading edge of the adjacent blade. An interesting phenomenon, i.e., the emergence of a local high pressure spot, is observed in the tip region. As a whole, it is concluded that there are two key effects of the emergence of the local high pressure zone in the tip region: (a) more leading edge spillage of tip leakage flow and increasing the risk to trigger stall; and (b) a decrease in blockage associated with doubleleakage of tip clearance flow within the influenced region of the local high pressure zone.

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.…”

“…In light of the same blade number for both rotors in the unsteady simulations, the fluctuation frequency of 1.0 BPF is identical to the sweep frequency of the two rotors. According to the previous study of the unsteady flow behaviors in R2, the frequency of 0.74 BPF is mainly due to the self-induced unsteadiness of TLF near the blade tip [37]. For the two CTs, two main findings can be seen in Figure 12b,c.…”

“…By comparing the common flow features of the two CTs, it can be inferred that both the vanishing of the low frequency components and the suppression of the TLF unsteadiness are beneficial to the SMI. According to the previous study of the unsteady flow behaviors in R2, the frequency of 0.74 BPF is mainly due to the self-induced unsteadiness of TLF near the blade tip [37]. For the two CTs, two main findings can be seen in Figure 12b,c.…”

“…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.…”