Effect of an Axially Offset Impeller on the Transient Physics of Asymmetric Flow in a Double-suction Centrifugal Fan

The impeller of a double-suction centrifugal fan may be subject to axial offset due to assembly or operational failure. The internal flow is asymmetric about the central disc and deteriorates the fan’s performance. In this work, the characteristics of flow were numerically investigated for the baseline model (Model-BM) and the axially offset impeller model (Model-Offset). The objective and motivation are to provide a detailed assessment and quantification of the effect of offset impeller on the fan’s performance and transient physics of the asymmetric flow. The numerical data reveal that the offset impeller generates highly asymmetric flow. The difference in mean flow rate at the two inlets of Model-Offset is 25.02m³/h, accounting for 6.8% of the total flow rate. The static pressure rise reduces by 2.40% for Model-Offset, and the static pressure efficiency is reduced by 2.11%. The leakage flow gets pronounced in the enlarged clearance with the inward and outward motion of air, while the narrowed clearance blocks it. The reversed flow is significant in the NA-side blade passages, especially close to the impeller end ring, where the leakage flow and the volute tongue confinement dominate. The reversed flow persists throughout the impeller, is still evident as the air first enters the volute, and is significant on the NA-side of the fan outlet.