Extending Highly Loaded Axial Fan Operability Range Through Novel Blade Design

Abstract

The tip clearance size has historically been considered to be the main factor affecting stability range in axial fan and compressors. This paper reveals that the stall characteristics are defined by the axial momentum flux of the tip leakage flow and that tip clearance is primarily a strong driver for this metric. A bespoke methodology for carefully tailoing the axial momentum via three-dimensional design is presented, which enables a higher degree of control over the stability range for cases where the tip clearance responds to other considerations and cannot be defined for this purpose. The effect of the axial momentum on efficiency is also addressed and the trade-off between operability range and design point performance derived. The results show that that the conditions for optimal stability differ from those for optimal efficiency and that control over the axial momentum enables tuning the design for a desired exchange. Numerical simulations have been employed to drive the analysis through a high-fidelity computational model whose behavior is supported by rich set of experimental data. Contrary to current belief, results further indicate that an accurate characterization of stall, including onset mechanism, can be achieved through steady-state simulations, minimising the need for expensive time-accurate computations during the design phase.

Analysis of a Modern Fan Manufacturing Variations and its link to the Engine Performance

“…The in-house code Hydra has been validated for this kind of turbomachinery flows versus various rig experimental data over many years, e.g. see Lopez et al (2022) for a similar blade. The turbulence method of choice is a helicity corrected Spalart-Allmaras (SA).…”

“…In particular, the authors addressed an unsteady phenomenon called APD (Alternate Passage Divergence) using a blade-to-blade stagger variation much larger than the one studied previously for the Buzz-Saw noise [e.g. by McAlpine et al (2006)]. They claimed that APD can adversely affect the aerodynamic efficiency and aero-mechanical stability and, unlike other types of off-design instabilities such as flutter, it can happen close to the fan operating point (i.e.…”