Design and Performance Investigation of a Double-layer Variable-geometry Centrifugal Fan

Conventional flow-control methods for centrifugal fans modify system resistance, inlet conditions, or rotational speed, which can compromise pressure regulation and aerodynamic efficiency under off-design conditions. As an alternative, this study proposes a double-layer variable-geometry centrifugal fan in which the effective flow-passage width is adjusted by varying the axial spacing between the two impeller layers and the corresponding volute components. Three-dimensional numerical models of an HRD-7-FU centrifugal fan were established for axial spacings of 100 and 200 mm. Aerodynamic performance and internal flow characteristics over 1900–2700 rpm were investigated using the Realizable k-ε model within the Reynolds-averaged Navier–Stokes framework, and the numerical predictions were assessed against representative experiments conducted at 2100 rpm. Under a common outlet back-pressure condition, axial spacing had a substantially greater effect on the mass flow rate than on the total-pressure rise. The 200 mm configuration delivered 1.89–2.03 times the mass flow rate of the 100 mm configuration and required 1.71–1.88 times the shaft power. Over 2100–2700 rpm, the two configurations showed comparable total-pressure-rise levels. The total-to-total isentropic efficiency ranged from 77.7% to 79.8% for the 200 mm configuration and from 75.5% to 78.2% for the 100 mm configuration. Dimensionless analysis revealed consistent trends in the flow and pressure coefficients for the two spacings. The internal-flow analysis further showed that axial spacing primarily influenced the extent of the endwall low-velocity regions, outlet-flow uniformity, and local turbulence levels, while the basic radial-pressurization pattern remained qualitatively similar for the two configurations. These findings clarify the aerodynamic response to variations in axial flow-passage width under the investigated configurations and operating conditions.