Volute-free centrifugal fans can find wide applications in ventilation systems. To make the volute-free centrifugal fan more compact in size, such as in the locomotive cooling system, the driven motor is often installed at the impeller eye. The installation of the motor blocks the flow passage to the impeller severely and may affect the fan’s aerodynamic performance evidently. However, such a blockage effect is often ignored in the design of the common centrifugal impeller. In this paper, numerical simulations are carried out to study the effect of the existence of the motor at the impeller eye. The results show that the choking effect of the motor has an obvious influence on the fan’s performance and must be taken into account in designing the impeller. The effects of the axial installation position and the supporting configuration of the motor on the characteristics of the fan are numerically investigated in detail. It is found that a shorter axial gap between the motor and the hub or the back plate of the impeller gives a better aerodynamic performance of the fan. In contrast, the cooling gap between the motor’s supporting barrel and the motor, and the struts for the barrel have little influence on the volute-free centrifugal fan’s aerodynamic performance. The results of numerical simulation agree well with the test results, which verified the rationality of considering the blockage effect of the pre-posed motor.

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