Unsteady characteristics analysis of compressors based on the proper orthogonal decomposition method

An aero-engine is often accompanied by a strong unsteady flow at near-stall condition, and increasing unsteady airflow eventually makes the engine unstable. To explore the unsteady flow characteristics, the Rotor 37 was taken as the research object. The unsteady flow characteristics of the blade tip flow field were analyzed using numerical simulation. The proper orthogonal decomposition (POD) was used to reconstruct the blade field, and the flow characteristics were analyzed. The results indicate that the unsteady characteristics of the tip area are mainly caused by the periodic evolution of the tip leakage vortex (TLV) and tip secondary vortex (TSV), and the interaction between the shock wave and tip leakage flow (TLF) plays a dominant role. The unsteady dominant frequency of the flow field upstream of the leading edge (LE) is consistent with the pressure surface and is ∼0.47 times the blade passing frequency (BPF), which is the main flow frequency. The first four POD modes can reconstruct the flow field well and successfully capture the high-energy pulsation structure in the upstream of the blade and the pressure surface flow field of the LE. The modes 1–2 frequencies are ∼0.48 times BPF, which is basically consistent with the conclusion of the prototype flow field and indicates that the periodicity of the TLV and TSV plays a leading role. The modes 3–4 frequencies are ∼0.96 times BPF, which captures the flow fluctuation near the LE. This fluctuation position is consistent with the TLV and reflects the low speed caused by the TLF.