Dynamic Mode Decomposition of the Unsteady Flow in a Vaneless Diffuser

Taking the simulation results under design condition 1.8 kg/s and unsteady condition 1.4 kg/s as the basic data, an analysis was conducted on the complex flow field in the vaneless diffuser of a centrifugal compressor using dynamic mode decomposition (DMD), so as to obtain the contours of tangential and radial velocity modes at 10% span plane as well as the characteristic frequencies, and to evaluate the applicability of DMD method in analyzing the unsteady flow within the vaneless diffuser. In addition, flow field reconstruction was conducted at different characteristic frequencies to figure out the transformation of unsteady flow in the diffuser. Results show that at small mass flow rates, the predominant effect of blade passing frequency is suppressed; the eigen mode corresponding to stall does not rotate along the circumferential direction, where three stall cells can be observed, and the frequency of stall is about 193 Hz.