This paper presents a numerical investigation on rotating instability in a low speed axial compressor. Full-annulus unsteady simulations were carried out to precisely simulate the circumferential propagating flow disturbances in the rotor tip region. Through long-term monitoring of the unsteady pressure signals, the multiple peaks of the broadband hump of rotating instability in frequency spectrum were successfully captured, which were in accordance with the results from casing pressure measurements. Frequency characteristics, azimuthal modal features and unsteady tip vortex structures were analyzed to interpret the source features and flow mechanism of rotating instability. Three vortex mechanisms have been found which induce circumferential propagating flow disturbance-tip leakage vortex oscillation with inter-blade-passage phase delay, detached vortex from tip leakage vortex and radial vortex near the leading edge plane. The tip leakage vortex oscillation with inter-blade-passage phase delay induce rotating flow disturbance with multiple modes including both long and short scale disturbances, which is considered as the original driving force of rotating instability. The multi-peak features of rotating instability are caused by the interaction between the short wavelength disturbance and the long wavelength disturbance, of which the mode order is unit. Though the number of detached vortex and radial vortex in one annulus agree with the mode order of rotating instability, that is rather the consequence than the cause of it.

This content is only available via PDF.
You do not currently have access to this content.