Performance gains provided by the use of a counter-rotating axial-flow fan with respect to a conventional rotor-stator stage

Abstract

The adoption of counter-rotating stages for propellers, axial-flow pumps and low-speed fans has opened a way to design high performance and compact turbomachines in various industrial domains, leading to potentially high savings in energy consumption. Because of the reduction of rotational speed and a better homogenization of the flow downstream of the rear rotor, these machines may have very good aerodynamic performances. However, they are rarely used in subsonic applications, mainly due to poor knowledge of the aerodynamics in the mixing area between the two rotors, where very complex structures are produced by the interaction of highly unsteady flows. The purpose of the present work is to compare the global performances (static pressure rise and static efficiency) and the wall pressure fluctuations downstream of the first rotor for three different stages operating at the same point: a single subsonic axial-flow fan, a conventional rotor-stator stage and a counter-rotating stage that have been designed with in-house tools. The counter-rotating stage allows large savings of energy with respect to the other two systems, for lower rotation rates and by adjusting the distance between the two rotors, a solution with comparable wall pressure fluctuations levels for the three systems is found.