The Use of Serrated Leading Edge for Inflow Conditioning in Centrifugal Fan

3.4 Fan Design for Improved Efficiency and Extended Operating Range

The design of air movement fans intended for industrial application is made challenging by the range of in-service conditions that must be accommodated. Each installation is unique, and typically constrained resulting in a distorted in-flow. The distorted in-flow classically results in lower fan efficiency. Severely constrained installations are characterised by in-flow dominated by separated flow features that degrade fan stability margin. Air movement fan designers must account for the impact of installation effects though both mechanically and aerodynamically robust design.
In this paper, we present a numerical study of a serrated centrifugal fan blade leading edge. The serrated feature minimizes the effect of distorted in-flow on fan stability and efficiency. The studied fan was designed for application in a roof-unit, laboratory tested with both original and serrated blade leading edges.
Numerical computations were performed using OpenFOAM with the cubic k-epsilon model of Lien and Leschziner. Performance of the studied fan was predicted with original and serrated blade leading edges with both un-distorted and distorted in-flow. Fan performance with two inlet distortions were predicted, with each distortion being chosen as characteristic of a different installation.
The paper concludes with a comparison of fan performance with and without the serrated blade leading edge when subjected to the un-distorted and two distorted in-flow. The impact of the serrated blade leading edge on fan stability and efficiency is considered, and the impact on in-service performance discussed. Implications for optimization of serrated blade leading edge geometry are then considered and the possible implication for long-term in-service reliability clarified.