Investigation of unsteady flow mechanisms and modal behavior in a compressor cascade

This paper utilizes experimentally validated Large Eddy Simulation method and the standard Dynamic Mode Decomposition (DMD) analysis technique to investigate the unsteady flow characteristics on a compressor cascade under two Reynolds number (Re) conditions (1.1 x 106 in ground state and 8.0 x 104 in high altitude state). The results demonstrate that at low Re, large-scale vortices are formed on the surface of compressor blades, exhibiting a stable rotating state and dominating the flow. Kelvin-Helmholtz instability serves as the determining factor, inducing chaotic and unstable behavior in the separation shear layer, leading to turbulence. Furthermore, DMD modal decomposition reveals a dominant mode at low Re, gradually amplifying and significantly contributing to the overall flow field, while showing strong correlations with other major modes. Conversely, at high Re, vortices on the blade surface become dispersed and smaller, resulting in intricate interactions between vortices of different scales. Harmonic instability, alongside Kelvin-Helmholtz instability, plays a significant role in accelerating boundary layer transition, heightening flow complexity and instability. Additionally, pronounced interaction and energy transfer between different modes occur at high Re, yielding a relatively balanced energy distribution. These findings have important implications for optimizing blade design and enhancing compressor performance by providing a deeper understanding of vortex dynamics and dynamic modal characteristics in the compressor blade flow field. (c) 2023 Elsevier Masson SAS. All rights reserved.

Automated summary

This study utilizes experimentally validated Large Eddy Simulation method and Dynamic Mode Decomposition analysis technique to investigate the unsteady flow characteristics on a compressor cascade under different Reynolds number conditions. The results show that at low Reynolds number, large-scale vortices dominate the flow, while at high Reynolds number, vortices become dispersed and smaller. The study also reveals the significant roles of Kelvin-Helmholtz instability and harmonic instability in the flow.