Circumferential propagation of tip leakage flow unsteadiness for a low-speed axial compressor

Abstract

Full-annulus three-dimensional unsteady numerical simulations were conducted for a low-speed isolated axial compressor rotor, intending to identify the behavior of self-induced unsteady tip leakage flow within multi-blade passages. There is a critical mass flow rate near stall point, below it, the self-induced unsteadiness of tip leakage flow can propagate circumferentially and thus initiates two circumferential waves. Otherwise, the self-induced unsteady tip leakage flow oscillates synchronously in each single blade passage. The major findings are: 1) while the self-induced unsteadiness of tip leakage flow is a single-passage phenomenon, there exist phase shifts among blade passages in multi-passage environments then evolving into the first short length wave propagating at about two times of rotor rotation speed after the transient period ends; and 2) the time traces of the pseudo sensors located on the rotor blade tips reveal another much longer length-scale wave modulated with the first wave due to phase shift propagating at about half of rotor rotation speed. Features of the short and long length-scale circumferential waves are similar to those of rotating instability and modal wave, respectively.