Instabilities in a turbulent swirling source flow between parallel rings

Abstract

Instabilities in a source flow between parallel rings with spatially modulated inflow conditions rotating at angular rate Ω are investigated in this Letter. Numerical simulations are conducted for five flow rates. Two inlet conditions are considered: an idealized one, in which the inlet flow is sealed, and a more realistic one, in which a leakage flow is entrained to enter the diffuser. The resulting fast Fourier transforms, wavelet analyses, and phase averages unravel the primary rotating instability that propagates in the parallel rings and leads to severe blockage for the mean flow. Moreover, secondary instabilities are triggered. Their identification is eased by the idealized inflow. We further discuss the imprinting of such instabilities in determining the route to chaos observed in the diffuser with more realistic inlet conditions. Special attention is here paid to identifying how the secondary instability mechanism is affected by the inflow.