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.

Centrifugal fans are widely used in different fields. The working fluid with high concentration of dust or coal ash could result in accumulations of dust or ash on the surface of impellor. Consequently, the fan or process system often has to be shut down unplanned to clean the dust or ash, to prevent harmful vibration of the rotor. In this paper, the main accumulating positions of dust and ash in impellor were firstly summarized. Then, a model of dust particle adhesion force judgment was established on the basis of static force analysis. Base on the analysis result, the influences of blade angle and blade radii on the dust-accumulating positions were discussed, which conformed to practical observations. After that, there introduces a low flow rate fan which cannot even be used in practical applications due to its inferior dust anti-adhesion ability. For this case, an optimization design with eight control variables was proposed to improve its anti-adhesion ability and efficiency. After six generations of optimization, the optimized results were clustered to two domains. Therefore, the searching areas were limited down to two areas which are determined by using clustering method in order to speed up the optimization process. The results of the numerical simulation of the gas-solid two-phase flow based on discrete phase model (DPM) showed that the new fan can run stably for a long-term.

In this paper, a transonic compressor cascade was optimized to improve its aerodynamic performance. A new blade parameterization method with 16 control variables was first proposed to fit the shapes of the suction and the pressure side, as well as the leading edge. Then, the Kriging surrogate-model-based genetic algorithm (GA) was used to optimize the performance of the transonic cascade. The optimization algorithm is effective in reducing the total pressure loss while extending the working range of the cascade. The results show that the total pressure loss coefficient could be reduced by 11% at the best airflow angle and the working range could be extended by 6.9% for the optimized cascade in two-dimensional simulations. Similar improvement results could also be obtained in the simulations of their linear cascade cases. Detailed analyses show that the relative maximum thickness positions of the optimized blades move forward by about 10% to the leading edge, and the radii of curvature of the front half of the suction and pressure surfaces increase, compared with the initial blade. This makes the front half of the optimized blades look more closely like a wedge. Consequently, the passage shock strength is reduced and the shock changes from the passage normal shock to oblique shock. The weakened shock strength leads to the disappearance of the flow separation caused by the shock boundary layer interaction on the suction surfaces of the optimized blades, and results in a narrowed wake width at the outlet section.

Squirrel cage fans (SCFs) are widely used in a variety of household appliances. Due to the restriction on installation size, the design of high-efficiency SCFs with high flow capacities is an important topic. In this study, we proposed a novel rounded rectangle volute profile (RRVP) for the design of compact high-flow SCFs. At first, we used computational fluid dynamics (CFD) to simulate the aerodynamic performances of three SCFs having the same impeller but different volutes, which were the common logarithmic-spiral volute profile, the cutting volute profile, and the RRVP volute at the maximum flow rate working condition. The CFD simulations indicate that the fan with RRVP volute has the highest flow rate at the maximum flow rate working condition. Then, we proposed a parameterization method for the RRVP with 16 control variables. The multiobjective evolutionary algorithm based on decomposition (MOEA/D) and Kriging model was used to optimize the aerodynamic shape of the compact SCF with an RRVP volute. Twenty-three control variables were used in the multiobjective optimization process, including the optimization of the blade angles and the impeller position. Optimization results show that the maximum volumetric flow rate of the optimal SCF with an RRVP volute increases from 147.1 cubic feet per minute (CFM) to 191.1 CFM, and the fan efficiency also increases from 32.21% to 33.5%, compared with the original SCF with the common logarithmic-spiral volute. Two main factors were found to increase the flow capacity and efficiency of the optimal SCF under strict size constrains. First, the RRVP became smooth and large, which reduced the flow loss and increased the flow cross-section; second, the eccentrically mounted impeller of the optimal fan enlarged the flow section near the outlet of the volute.

The high flow-rate centrifugal fan needs a three-dimensional impeller to achieve a high efficiency. In this paper, the design procedure of a high-efficiency three-dimensional centrifugal fan is presented. First, the main dimensions of the fan were calculated by using the conventional one-dimensional method. Then, the blade loading or the angular momentum distribution along the meridional streamline on the blade surfaces is prescribed. After that, the three-dimensional blade is determined by using the streamline curvature method. With the aid of numerical simulations, the performance of the three-dimensional fan was improved and some of the key influence factors were investigated. The analyses indicate that, as to the high flow-rate centrifugal fan, the Stanitz modified formula is recommended to calculate the separation radius, r b . A proper increase in the separation radius is beneficial for the fan's performance. It is also indicated that a decrease in the angular momentum on the hub leads to an increase in total pressure efficiency, under the condition of a given constant mean angular momentum at the outlet of the blade. In addition, the installation of a fairing on the hub plate can improve the fan's efficiency evidently when the streamline curvature method is adopted to design the three-dimensional impeller.