Suppression of Flow Instability and Mitigation of Performance Degradation in Compact Axial-Flow Fan with Upstream Obstacle Using Grid-Type Filter

We propose installing grid-type filters at compact axial-flow fan inlets to suppress flow instability and prevent degradation of fan performance in environments with an upstream obstacle. The effectiveness of this approach was investigated primarily through experiments, complemented by computational fluid dynamics analyses to investigate the flow-instability suppression mechanism. We examined the effects of different combinations of the main filter design factors such as mesh size (the area of a unit grid cell) and porosity (open-area ratio) on (i) the flow-rate range over which flow instability occurs and (ii) the performance and efficiency curves of the compact axial-flow fan in the presence of an upstream obstacle. As a result, installing grid-type filters at the fan inlet successfully suppressed the flow instability. An annular grid‑type filter was more effective in reducing pressure loss than a circular grid‑type filter. Furthermore, both single‑ and multi‑objective Bayesian optimization were applied to the experimental results, and we identified optimal specifications for the grid‑type filters, which were subsequently validated by experiments.