Design of axial flow fans for reduced noise and improved efficiency



Axial flow fans are used in a wide variety of applications, from cooling systems for electronics to ventilation in buildings.  Whatever the application, there will be competing design constraints which make it difficult to achieve the required pressure-flow performance characteristic, within a specified space envelope, whilst meeting a target aerodynamic efficiency and noise level.

This paper describes a design methodology for optimizing aerodynamic performance and noise.  It is based on use of a semi-analytic 2-D design tool for preliminary predictions and design, combined with a 3-D numerical CFD analysis to visualize the flow.  Both models can be extended to the design of multi-stage systems.

The 2-D model predicts the flow velocity at the trailing edge of the blades for each point on the fan performance curve, which is then used to estimate self-noise characteristics of the rotor using a classical model of airfoil trailing edge noise.  The CFD analysis provides detailed validation of assumed airfoil characteristics, including the effect of 3D design features such as blade sweep, and confirms the flow and aerodynamic efficiency predictions; it can also used to estimate parameters such as turbulence intensity that is a key driver for the noise level.