An Overview of Axial Fans

Axial fans have become indispensable in everyday applications starting from ceiling fans to industrial applications and aerospace fans.  The fan has become a part of every application where ventilation and cooling is required, like in a condenser, radiator, electronics etc., and they are available in the wide range of sizes from few millimeters to several meters. Fans generate pressure to move air/gases against the resistance caused by ducts, dampers, or other components in a fan system. Axial-flow fans are better suited for low-resistance, high-flow applications and can have widely varied operating characteristics depending on blade width and shape, number of blades, and tip speed.

Fan Types

The major types of axial flow fans are: propeller, tube axial, and vane axial.

  • – Propellers usually run at low speeds and handle large volumes of gas at low pressure. Often used as exhaust fans these have an efficiency of around 50% or less.
  • – Tube-axial fans turn faster than propeller fans, enabling operation under high-pressures 2500 – 4000 Pa with an efficiency of up to 65%.
  • – Vane-axial fans have guide vanes that improve the efficiency and operate at pressures up to 5000 Pa. Efficiency is up to 85%.
Types of Fans
Figure 1 Different Types of Axial Fans
Aerodynamic Design of an Axial Fan

The aerodynamic design of an axial fan depends on its applications. For example, axial fans for industrial cooling applications operate at low speeds and require simple profile shapes. When it comes to aircraft applications however, the fan must operate at very high speeds, and the aerodynamic design requirements become significantly different from more traditional fan designs.

Figure 2 Types of Axial Fan Based on Applications
Figure 2 Types of Axial Fan Based on Applications
  • – To generate an efficient axial fan, the flowpath should be properly sized (i.e. tip diameter, blade height etc.) along with the optimal inlet/outlet blade angle selection and the corresponding blade profile that should have minimal profile and secondary losses.
  • – As an aerodynamic engineer, it is important to understand the flow along the blade height for which the designer can control the inlet swirls and blade loading by altering the blade angle distributions from hub to tip.

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The design cycle time for fans can be considerably reduced using well established turbomachinery design software tools such as AxSTREAM®. Using such programs not only reduces the design cost, but also gives the best performance for the specified application, as the user can evaluate the entire design space in which the fan has to operate.

The design cycle time for fans can be considerably reduced using well established turbomachinery design software tools such as AxSTREAM®. Using such programs not only reduces the design cost, but also gives the best performance for the specified application, as the user can evaluate the entire design space in which the fan has to operate. The AxSTREAM® platform also provides opportunities for designers to analyze the design using the 1D/2D solver where the designer can control different flow distributions from hub to tip using different types of blade twists.

 

Figure 3 (a) Blade angle distribution from hub to tip for different Twist factors
Figure 3 (a) Blade angle distribution from hub to tip for different Twist factors
(b) Specific Work distribution for different Twist factors

After that, the designed fan can be analyzed for the flow physics and behavior using 3D CFD (Computational Fluid Dynamics).  AxCFD™ within the AxSTREAM® platform helps users to quickly perform a 3D CFD analysis for the design and off-design conditions with automated mesh generation and post-processing. The results of 3D CFD is presented in the figure below.

Figure 4 3D model and CFD modelling in AxSTREAM
Figure 4 3D model and CFD modelling in AxSTREAM®

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