This has showed an improvement in both uniformity of the flow and pressure drop.

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Abstract

In this thesis computational fluid dynamics (CFD) simulations are carried out on a two-stage axial flow fan manufactured by Fläkt Woods. The fans are used in modern boiler plants.

Geometrical modifications of the two-stage axial flow fan are investigated theoretically with the aim to improve the efficiency and reduce the noise of the fan. As a consequence the cost for electricity and acoustic treatment for the boiler plant will be lowered. These modifications are adjustments of the upstream curvature of the guide vanes in front of the first impeller and an increase of the size of the inlet box or introduction of two extra guide vanes in the inlet box. Two properties, directly related to sound generation of the fan are, used in the optimization: 1) high uniformity of the flows upstream of the first rotor and 2) low pressure drop in the inlet box.

The engineering finite element software COMSOL Multiphysics, is used for the geometrical modifications in the model and the CFD simulations.

The simulations have shown that the best geometrical modifications investigated in this thesis is to increase the size of the inlet box. This has showed an improvement in both uniformity of the flow and pressure drop.

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