A high-efficiency centrifugal fan with low noise emission is used to investigate the influence of the casing width on the flow performance. Common design concepts use a width ratio of casing to impeller outlet from 2.5 up to 3. This range of the width ratio results in a large casing depth, which is not the best approach with regard to the overall dimension and the material costs for large industrial machines. Furthermore, centrifugal fan designs with a width ratio above 3 are disadvantageous because of their lower overall efficiency. In addition to an optimized casing depth, the position of the impeller in the casing also influences the performance. Using the results of several CFD simulations, we show that by creating a very small gap between the impeller rear plate and the casing wall, smaller energy losses and higher–performance can be achieved.

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