Abstract
The volute-free centrifugal fans in ventilation applications are used to exhaust a large amount of air under the effect of the head loss in the ventilation pipeline system, thus, a high static pressure rise at a large flow rate of the fans is anticipated. The shroud of the conventional volute-free centrifugal fans has an axisymmetric geometry, that is, the height of the fan outlet is constant over the whole circumference. Considering the non-uniform flow in the blade passages, the shroud of a wavy geometry might help in improving the static pressure rise and efficiency of the fans at a large flow rate condition. In this work, we performed a numerical investigation on the internal flow of a volute-free centrifugal fan with a wavy shroud. The effect of the geometry of the wavy shroud, as quantified by the maximum height and profile, on the aerodynamic performance of the fan is explored, and the flow physics leading to the performance improvement are demonstrated through a detailed analysis of the patterns of the internal flow. The numerical results showed that compared with the baseline fan with an axisymmetric shroud, the fan with a wavy shroud could substantially improve the static pressure rise and efficiency at the large flow rate. The wavy shroud regulates the near-wall flow especially at the fan outlet; the fluctuation of the radial velocity, secondary flow, and reversed flow is greatly weakened, producing a uniform flow at the fan outlet. The fluctuation of the static pressure in the blade passages and on the shroud side of the fan outlet greatly decreases. Further analysis of the acoustic power level field indicates that the wavy shroud increases the acoustic power at the fan inlet but does not have a notable influence on that near the outlet.
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