Circumferentially Non-Uniform Flow in the Rear Stage of a Multistage Compressor

Abstract

Full annulus midspan URANS simulations are performed to examine wake interaction for rows with different blade counts. The amount of non-uniform flow is studied particularly in the rear stages of a 3.5 stage compressor with a different blade count at all rows. A high-performance cluster was used for the required full annulus URANS simulations. Due to the high numerical effort, three representative operating points are investigated in quasi-3D. The simulations are performed at a midspan stream tube which take into consideration the contracting duct of the compressor. The results indicate two main effects: wake-wake interference and wake-airfoil interaction. Both effects are related to the particular clocking position, which affect each other accordingly. At the aerodynamic design point, non-uniform flow at the rear stage has a significant impact. Intensified unsteady wake-airfoil interaction near the surge line causes circumferential unequal flow separation. Close to choke, the shock strength depends on the Mach number, hence jet and wake inflow affects different losses. The frequently used assumption of periodic flow disregards the deviations shown. Based on the numerical results, the accuracy of performance measurements is presented. Non-uniform flow causes inaccuracy of more than one percentage point for stage and compressor performance measurements, which is more than commonly requested. In summary, interaction of rows with dissimilar blade count leads to non-uniform flow in rear stages that needs to be considered in performance measurements.