Grant: Alliance Grants

All fans are subject to limits on their ability to operate at flow rates lower than the design value due to flow instabilities such as rotating stall, in which flow breaks down in the space between two blades of the compressor, leading to a large drop in pressure rise and flow rate. To computationally predict the onset of this phenomenon requires high-fidelity, time-resolved computations which are most efficiently run in parallel with a large number of computing cores (either central processing units (CPUs) or graphical processing units (GPUs), depending on the software). This research project aims to identify the trade-offs between accuracy and computational cost for a variety of computational fluid dynamics (CFD) based approaches to determining the stalling flow rate for jet engine-style fans. Currently, fully resolving the stall inception process leads to very accurate predictions but computational costs that are not practical to include into the design process, so design guidelines must be conservative; this suggests that it is possible fan (and thus overall engine) efficiency could be improved while still maintaining acceptable stall margin if accurate design-time assessments could be made. This problem becomes even more important when considering inlet flow distortions, where the inflow velocity varies over the fan inlet area. This can lead to stall occurring at higher overall flow rates than with uniform inflow, and requires more expensive computations because the full fan wheel must be resolved. Recent advances in simplified fan modelling and turbulence modelling provide potential paths for stall prediction at significantly reduced cost, but these have not been assessed for inlet flow distortion. In this project, these will be assessed quantitatively using a GPU-based CFD code, Turbostream, whose developer is a partner on the project. To ensure accurate results, an experimental low-speed fan rig will be designed and fabricated, and computations will be carried out for both that design and a high speed version. This work is important to the Canadian aerospace industry and the other project partner Pratt & Whitney Canada to ensure continued competitiveness and reduced environmental impact from future aircraft in Canada and globally.