Investigation of Reynolds number effects on flow stability of a transonic compressor using a dynamic mode decomposition method.

• Re effect leads to higher frequency and stronger circumferential momentum of compressor tip leakage flow. • Impact of tip leakage flow decreases from leading edge to mid-chord, but increases from mid-chord to trailing edge at low RNI condition. • Flow instability, identified by DMD, shows growth of low-frequency stall modes and weakening of blade-passing modes. • High RNI condition exhibits non-uniform high-pressure region due to shock-TLV (tip leakage vortex) interaction, leading to delayed flow field response to blade passing. • Low RNI condition results in uniform high-pressure region due to enhanced circumferentia momentum of tip leakage flow, leading to secondary leakage formation. With the continuous increase in aircraft flight altitude, low Reynolds number effects in high-altitude environments significantly impact the stability of compressor operation. In this study, dynamic mode decomposition (DMD) of the flow field at various time instances near stall conditions in a transonic compressor was performed to investigate the influence of Reynolds number (Re) effects on critical flow characteristics and instability mechanisms. The results indicate that under different Reynolds number index (RNI) conditions near stall conditions, the frequency of tip leakage flow varies. Under high RNI condition, the influence of tip leakage flow is concentrated mainly from the leading edge to the mid-chord. The stall mode is primarily caused by the interaction of shock with the Tip Leakage Vortex, resulting in the breakdown of the vortex. The development of vortex structures inside the passage leads to a delay in the flow field response to blade passing. Under low RNI condition, the tip clearance leakage flow is stronger, with a relatively reduced influence from the leading edge to the mid-chord and an increased impact from the mid-chord to the trailing edge. The main cause of the stall mode is the circumferential movement of vortex structures, causing secondary leakage over adjacent blade tip clearances. The blockage formed by vortex structures within the passage is weaker, and the flow field response to blade passing remains consistent with the blade passing frequency. However, as stall develops further, the flow field response significantly decreases. [ABSTRACT FROM AUTHOR]