Circumferential Mode Analysis of Axial Compressor Tip Flow Using Fourier Transform and Proper Orthogonal Decomposition

Rotating instability (RI) of a single-stage axial compressor was studied by both numerical and experimental methods. A circumferential mode decomposition method based on spatial Fourier transform was used to analyze the circumferential pressure distribution of the tip flow. Circumferential mode characteristics were captured both on blade passing frequency (BPF) and rotational instability frequency (RIF) under several flow conditions. The characteristic spectrum of RI with broadband hump existed in a large range of flow conditions. Both frequency range and dominant circumferential mode number decreased with flow rate, while circumferential angular velocity of RI increased at the same time. On the other hand, a proper orthogonal decomposition (POD) method was applied to obtain the mode component of tip flow. The feature of tip flow was analyzed with the help of POD mode vector and mode amplitude. The influence of the decrease on the spatial monitor points in POD method was analyzed using CFD data to analysis the potential error from experimental results. It is expected to deeply understand the mechanism of the rotating instability and rotor-stator interaction phenomenon by spatial FT and POD methods in this study.