Propagation of Different Types of Inflow Distortions through a Contra Rotating Fan Stage

Abstract

This paper aims to explain the propagation of different types of inflow distortions through a contra rotating fan stage. Inflow distortions like circumferential, radial and complex distortions were artificially generated using meshes of different porosities. The overall effects of these distortions are determined in the terms of the fan performance map. It is attempted to explain the propagation of inflow distortion using distortion descriptors like circumferential intensity, circumferential extent and radial intensity at the design mass flow rate. These are described for different speed combinations of both the rotors at the inlet, the exit of rotor-1 and at the exit of rotor-2. It is important to observe here that even for purely circumferential inflow distortion, the distortion does not remain purely circumferential, rather it propagates both circumferentially and radially along the stage. For the hub-strong complex inflow distortion, the higher magnitude of circumferential intensity and circumferential extent at the exit of rotor-1 clearly indicates the strong distortion effect that leads to poor performance of the stage amongst all distortion configurations studied. With radial inflow distortion, the radial redistribution of the flow at the exit of rotor-1 plays an important role in the performance of the rotor-2 and thereby for the stage.