Effect of Motor Blockage on Transient Characteristics of Asymmetric Flow in a Double-suction Centrifugal Fan

The double-suction centrifugal fan is typically installed in the ventilation unit and driven by a motor beside it. One of the two inlets of the double-suction fan is partially blocked by the motor, and the flow in the fan becomes asymmetric and non-uniform. This work numerically investigated the effect of the motor blockage on the transient characteristics of the asymmetric flow in a centrifugal fan. The distance between the motor and the adjacent collector is typically 20mm or 40mm. Numerical results reveal that compared with the baseline motor-free model, the motor blockage of the two models decreases the flow rate by 30.4% and 20.8%, respectively, at the obstructed inlet of the fan, and the inflow is non-uniform and presents a local reversed flow. The motor blockage decreases the static pressure efficiency by 9.45% and 6.04%, respectively, while the static pressure rise is hardly affected. The flow fluctuation is notably asymmetric and non-uniform due to the non-axisymmetric geometry of the volute and the motor blockage. The blade passages are occupied by strong reversed flow, and a low-pressure region exists in the impeller. This work also performed a comparative study on the correctness and applicability of the boundary condition. The type of boundary condition of constant pressure at the outlet and a flow rate at the inlet, which is a common choice for fans without considering the obstacles, is analyzed. It was found that this type of boundary condition underestimates the efficiency of the fan with motor blockage, and the pressure field at the fan inlet is considerably different.