Large eddy simulation on the vortex evolution in a squirrel-cage fan based on a slice computational model

To investigate the hard-to-measure complex flow in a squirrel-cage fan, a slice model was established in the present study to perform a partial large eddy simulation calculations on an r-θ sectional flow field instead of the large-scale and time-consuming full three-dimensional flow calculations. The method used to build the slice model was first introduced, and then the model was verified by the results obtained by other models and flow measurements. It is shown that to calculated the correct flow field and detailed vortex evolution, the Courant number of the slice model should be below 1, and the model thickness should be at least 2.4% of the impeller outer diameter. Through this simplified model, vortex evolutions rarely observed in other studies were successfully captured, such as vortex shedding caused by leading-edge separation, periodic backflow in the blade cascade, and vortex cluster traveling across the impeller. The flow separations were also illustrated on the inner surface of the volute tongue, accompanied by tiny and high-frequency eddies. The evolution process and frequency characteristics of these flow patterns were analyzed in detail, providing references for the design and noise reduction of this type of fan.