Effect of a Radially Offset Impeller on the Unsteady Characteristics of Internal Flow in a Double-Suction Centrifugal Fan

Abstract

The impeller of double-suction centrifugal fans may be radially offset from the centerline of the volute due to faults in assembly or installation. The radial offset results in the more significant non-uniformity of internal flow in the centrifugal fan, which is biased from the designed condition, and deteriorates the aerodynamic performances of the fan. In this paper, we performed Unsteady Reynolds-averaged Navier–Stokes (URANS) simulations on the unsteady internal flow of a double-suction centrifugal fan. The impeller of the fan is offset in the radial direction from its original position and is thus closer to the wall of the volute on one side and away from the opposite side. Numerical results show that the offset impeller changes the size of the gap between the impeller and collector in the radial direction, which produces a non-uniform distribution of static pressure and even reversed flow at the inlet of the impeller. As the impeller is offset away from the baffle of the volute, reversed flow back into the volute is observed, and strong circulating vortices form around the baffle, which weakens the diffusing capability of the volute. However, as the impeller is offset close to the baffle, the internal flow of the volute generally improves the flow patterns within the impeller, while the boundary layer separates from the pressure surface of the blades near the front disc as the flow angle varies; the maximum velocity of reversed flow could reach 20 m/s which lowers the efficiency of the fan.