Effect of Leading Edge Tubercles on Compressor Cascade Performance

TL;DR

This study investigates how leading edge tubercles on compressor blades affect cascade performance, showing they can delay stall and potentially improve axial compressor operation.

Contribution

It provides experimental evidence that leading edge tubercles increase stall angle and flow stability in compressor cascades, a novel application for stall mitigation.

Findings

Stall angle increased up to 8.6° with tubercles.

Flow visualization shows altered flow passage near tubercles.

Hot-wire measurements indicate flow modifications near blade surface.

Abstract

Tubercles are modifications to the leading edge of an airfoil in the form of blunt wave-like serrations. Several studies on the effect of tubercles on isolated airfoils have shown a beneficial effect in the post-stall regime, as reduced drag and increased lift, leading to a delay of stall. The prospect of delaying stall is particularly attractive to designers of axial compressors in gas turbines, as this leads to designs with higher loading and therefore higher pressure rise with fewer number of stages. In the present study, experiments were performed on a cascade of airfoils with NACA 65209 profile with different tubercle geometries. The measurements were made over an exit plane using a five-hole probe to compare the cascade performance parameters. Additionally, hot-wire measurements were taken near the blade surface to understand the nature of the flow in the region close to the tubercles. Oil-flow visualization on the cascade end wall reveal the flow through the passage of blades with and without tubercles. For the cascade considered, the estimated stall angle for the best performing set of blades is found to increase up to 8.6{\deg} from that of the unmodified blade of 6.0{\deg}. Application of such structures in axial compressor blades may well lead to suppression of stall in axial compressors and extend the operating range.