Experimental Study of the Effect of Radially Distorted Inflow on a Contrarotating Fan Stage

Abstract

The paper reports results of a detailed study of hub-and tip-strong radial inflow distortion on the performance of a low speed, high aspect ratio (3.0) contrarotating fan stage. The distortion screen (placed upstream of the first rotor) covers 1/3 of the span of the blade near the hub and the casing for hub-strong and tip-strong inflow distortions, respectively. The performance of the contrarotating fan was investigated under both the radially distorted inflows and compared with the clean inflow conditions under different speed combinations of rotor-1 and rotor-2. The hub-strong radial distortion reduces the overall performance (pressure rise and efficiency) as well as the operating range by about 2 to 4% under the different speed combinations. On the other hand, it is interesting to observe that the tip covered radial distortion not only improves the pressure rise, but also increases the overall operating range by about 6 to 8%. There was, however, a 6 to 8% decrease in efficiency in this case as compared to 12 to 15% for hubstrong radial inflow distortion. The results reveal the physics of the effects of radial inflow distortion on the overall performance of the contrarotating fan stage.

Influence of distorted inflows on the performance of a contra-rotating fan

“…The screens are placed at the inlet of the stage, at a distance of 2.84 times the casing radius from rotor-1. The wired mesh screens for the hubradial distortion and the tip-radial distortion conditions extend up to 0.33% of the span from the hub and 0.2% of the span from the tip, respectively [30] . The wired mesh screen for the simple circumferential distortion condition extends to 90 • .…”

“…Generally, radial and circumferential distortions reduce the loading and the stability margin of the stage. However, tip-radial distortion resulted in a small improvement in loading at certain flow coefficients [30] . Under circumferential distortion, the distorted region of the flow initially propagates in the direction of rotation of rotor-1 as the flow crosses rotor-1, and later in the direction of rotation of rotor-2 as the flow crosses rotor-2.…”

“…A study on an axial fan with radial distortion blades identified that the modal waves leading to stall had a significant effect due to the flow near the hub region [29] . A few recent works have analyzed the characteristics of a high-aspect-ratio CRAF under radial and circumferential distortions [30,31] . Generally, radial and circumferential distortions reduce the loading and the stability margin of the stage.…”