The Complete Guide to Axial Fan Design and Simulation

Axial fan design is a complex process that requires careful consideration of various factors to achieve optimal performance.

A well-designed axial fan can achieve a high airflow rate, with some fans able to move up to 10,000 cubic feet per minute.

Axial fans are widely used in various applications, including industrial ventilation, HVAC systems, and computer cooling.

The design of an axial fan is crucial in determining its efficiency and performance, and it's essential to consider factors such as fan size, blade angle, and motor power.

In axial fan design, the fan size is a critical factor, with larger fans typically able to move more air than smaller ones.

A typical axial fan has a hub diameter of 100-500 mm and a blade length of 50-200 mm, depending on the application.

For another approach, see: Minimum Size of Walk in Shower

A typical input for a detailed simulation analysis is a watertight (wet) surface model in form of STL surface. This model is essential for CFD simulation, where a closed watertight model of the fan inner parts is required.

The CAD model of the axial fan can be created in any CAD software manually or in an automated way via parametric model. Engineers can also use dedicated software for turbomachinery design, such as CFturbo, Concepts NREC, or TURBOdesign Suite.

To create a complete rotor (impeller) component CFD domain, you need to define parameters like Axis and Flange_center. For example, Axis = “x” and Flange_center = [0.0, 0.0, 0.150] will lead to a complete rotor (impeller) component CFD domain ready for simulation.

The rotor and stator components are created in a similar way, and the full axial fan geometry would be following: rotor-shroud.stl

A smooth transition from inlet blade tip to outlet blade tip is assumed in the theory on which this calculator is based. This theory, credited to Charles Innes, has been the industry standard since 1916.

To follow the rules, always try to use a backward facing blade where possible, as it generates more head (pressure) and is much more efficient.

Consider reading: Design Software for Furniture

The calculation of parameters for axial fans involves considering a mean velocity triangle for flow only through an infinitesimal blade element. The blade is divided into many small elements, and various parameters are determined separately for each element.

There are two main theories used to solve the parameters for axial fans: Slipstream Theory and Blade Element Theory. These theories help engineers determine key parameters such as the diameter of the propeller disc and the diameter at the exit.

The area of the propeller disc can be calculated using the formula for the area of a circle, which is πr^2, where r is the radius of the disc. The mass flow rate across the propeller is also an important parameter, which can be calculated using the formula for mass flow rate.

Here are some key design parameters for axial fans:

The axial thrust on the propeller disc due to change in momentum of air is also an important parameter, which can be calculated using the formula for change in momentum. The efficiency of the axial fan can be determined using the expression for efficiency, which takes into account the lift coefficient and drag coefficient.

For more insights, see: Type B Roof Deck

Calculating the parameters of an axial fan is a crucial step in designing one. It's essential to consider the mean velocity triangle for flow only through an infinitesimal blade element.

The blade is divided into many small elements, and various parameters are determined separately for each element. There are two theories that solve the parameters for axial fans: Slipstream Theory and Blade Element Theory.

The diameter of the propeller disc (D) and the diameter at the exit (Ds) are key parameters to consider. The area of the propeller disc of diameter D is calculated using the formula: area = π × D^2 / 4.

The mass flow rate across the propeller is given by the formula: mass flow rate = ρ × A × V, where ρ is the density of the fluid, A is the area of the propeller disc, and V is the velocity of the fluid.

The axial thrust on the propeller disc due to change in momentum of air is calculated using the formula: thrust = Δm × V, where Δm is the change in mass and V is the velocity of the fluid.

The efficiency of the axial fan can be expressed as: efficiency = (thrust / (ρ × A × V^2)) × 100.

Lift Coefficient (CL) and Drag Coefficient (CD) are also important parameters in axial fan design, and are typically given for specific applications such as ventilation fans, mechanical engineering, turbomachinery, and gas technologies.

Here are the formulas for the area of the propeller disc and the mass flow rate across the propeller:

Paralleling can be a problem when multiple fans are used together.

This effect is seen only in case of multiple fans.

Comparing the air flow capacities of the fans can cause noise, specifically referred to as Beating in case of fans in parallel.

Differing inlet conditions can help avoid beating.

Differences in rotational speeds of the fans can also help avoid beating.

To avoid beating, use differing inlet conditions, differences in rotational speeds of the fans, etc.

Blade design is a crucial aspect of axial fan design. The number of blades (z) and spacing (s) are related as s = 2πr/z, where r is the distance from the root of the blade.

In order to create a workable solution, it's essential to follow the rules of the theory, such as always trying to use a backward facing blade where possible. This generates more head (pressure) and is much more efficient.

A smooth transition from inlet blade tip to outlet blade tip is also necessary, as any irregularities can lead to inefficient airflow. The two blade tip angles define the profile of your blade.

Here are some key guidelines to keep in mind when designing blades:

By following these guidelines and understanding the relationships between blade design and airflow, you can create a more efficient and effective axial fan.

The number of blades in an impeller is a crucial design consideration. A 1-blade design is extremely inefficient due to turbulent airflow behind each blade.

Too few blades, like 1 or 2, can lead to turbulence and reduced operational efficiency. This is because the air trailing each blade will be turbulent, making your fan less effective.

On the other hand, too many blades will also reduce fan efficiency through increased skin friction and impeller mass. A 6-blade design, for example, will start to see losses from increased skin friction and mass begin to exceed airflow gains.

A 5-blade configuration is generally the best choice for medium aspect ratio impellers. This is because it strikes a balance between airflow and skin friction.

If you're designing a centrifugal fan, you'll need to consider the aspect ratio of your impeller. A high aspect ratio (0.75<φ<1.0) is typically used for high-pressures and low flow rates.

The radial depth of a high aspect ratio impeller is relatively shallow compared to its outer diameter (OD). This is important to keep in mind when designing your impeller.

In contrast, a medium aspect ratio (0.5greater flow rates but reduced pressure potential. This is a common choice for centrifugal fans.

Regardless of the design criteria, an impeller's aspect ratio should ensure that its airflow is not compromised. This means that the impeller inlet area should be no less than the inlet area of the blades.

Check this out: Centrifugal Fan

Centrifugal (Blade Design) is a crucial aspect of fan design, and understanding the basics can make a huge difference in performance and efficiency.

The number of blades on a centrifugal fan can significantly impact airflow and efficiency. Too few blades can lead to turbulent airflow, reducing operational efficiency, while too many blades can increase skin friction and impeller mass.

A 1-blade design is extremely inefficient, with airflow occurring in only about 1/3rd of the impeller volume, while 2-blade designs still generate significant turbulence. On the other hand, 3-blade designs are excellent for small aspect ratio impellers and are simpler to balance.

For medium aspect ratio impellers, 5 blades is the best configuration, while 6 blades or more can lead to losses from increased skin friction and mass. It's also essential to ensure that blades don't overlap.

When designing blades, it's essential to follow the industry standard theory, credited to Charles Innes, which assumes a smooth transition from inlet blade tip to outlet blade tip. The two blade tip angles define the profile of your blade, and getting it wrong can lead to meaningless results.

Curious to learn more? Check out: Centrifugal Fan Design

Always try to use a backward-facing blade, as it generates more head and is more efficient. Paddle blades should be 90° inlet and outlet, while inlet blade angles should be considerably less than 90°. When setting blade outlet angles greater than 90°, ensure the inlet blade angle is shallow enough to overcome inward thrust from the outlet tip.

A different take: Aircon Fan Blade

As we explore the world of axial fan design, it's essential to understand the performance and efficiency characteristics of these fans.

The relationship between pressure variation and volume flow rate are crucial performance characteristics of axial fans. The performance curve for the axial fan shows that as the flow rate increases from zero, efficiency increases to a particular point and then decreases.

Efficiency peaks at a specific point, after which it starts to decline. This is a key consideration in axial fan design, as it directly impacts the fan's overall performance.

The power output of axial fans increases with a nearly constant positive slope. This means that as the fan's flow rate increases, its power consumption also increases at a steady rate.

At low discharges, pressure fluctuations are observed, which can lead to unsteady flow. This can be mitigated by optimizing the fan's design and operating conditions.

Here are the key performance characteristics of axial fans, based on the performance curve:

Stalling and surging are undesirable effects that can occur in axial fans, causing performance issues, noise generation, and affecting the blades and output.

These effects are often caused by improper design, fan physical properties, and can be reduced by designing fan blades with a proper hub-to-tip ratio.

Analyzing performance on the number of blades and minimizing the effects of stalling can be achieved by operating axial fans at low speeds, using guide vanes to control and direct the flow, and making the flow laminar by introducing a stator to prevent turbulent flows at the inlet and outlet of the fans.

The stall zone for single axial fans and axial fans operated in parallel should be avoided to prevent stalling effects, and operating in a safe zone can help maintain optimal performance.

On a similar theme: Hvac Zone System Design

Improper design and physical properties of fans can lead to unstable flow, causing stalling and surging, which affects fan performance and output.

To avoid unsteady flow, designing fan blades with a proper hub-to-tip ratio is crucial. This helps prevent flow separation on the blade surface.

Analyzing performance based on the number of blades can also reduce these effects. By using guide vanes, you can control and direct the flow, minimizing the risk of stalling.

Re-circulating excess air through the fan is another method to reduce stalling effects. Operating axial fans at high efficiency requires operating them at low speeds.

Turbulent flows at the inlet and outlet of the fans can cause stalling, so making the flow laminar by introducing a stator can prevent this effect.

Here are some key takeaways to prevent unsteady flow:

By following these methods, you can prevent unsteady flow and ensure stable fan performance.

The Meridional Average is a valuable tool for turbomachinery engineers, allowing them to visualize the distribution of total pressure or velocity along the meridian plane.

By projecting results circumferentially and onto the meridian plane, engineers can gain a clearer understanding of how energy or velocity is distributed through the fan.

This method effectively avoids the holes (blades) that can make it difficult to interpret data, providing a 2D interpretation of the flow through the fan.

Engineers can use the Meridional Average to see how total pressure or velocity are distributed along the meridian, giving them a more complete picture of the flow.

The axial fan design process relies heavily on computational fluid dynamics (CFD) simulations, which provide valuable insights into the fan's performance. A CFD simulation setup for an axial fan involves using the TCFD software module, which is part of the TCAE software.

The simulation is managed in the TCFD GUI in ParaView and uses the OpenFOAM open-source application. Simulation parameters such as fan type, time management, physical model, and wall roughness are also specified.

For the axial fan design, the simulation is set up to run in steady-state mode with a speed of 3000 RPM and an outlet static pressure of 0 m2/s2. The turbulence model used is k-omega SST, and the wall treatment is set to wall functions.

If this caught your attention, see: Creative Wall Clock Designs

TCAE software is a powerful tool for simulating and analyzing complex systems, such as axial fans. It can drastically reduce simulation time by simulating just a single blade periodic segment of the machine.

The software allows users to split the axial fan into several waterproof components due to rotation, making it easier to perform high-tech simulations. Each component consists of a few or multiple STL surfaces, which can be split further into individual surfaces.

For CFD simulation, the final model needs to be split into closed waterproof components. In the case of an axial fan, it's reasonable to split it into two components: Rotor and Stator. The Rotor component can consist of individual STL files such as the rotor inlet, outlet, wall, and blade surfaces.

A simple structure of surface files is often sufficient and easier for simulation setup, but a more complex structure allows for more possibilities in performing high-tech simulations. The software also allows users to change the number of components or individual surfaces, giving them flexibility in their simulation setup.

The computational mesh for CFD is created using the snappyHexMesh open-source application, and all mesh settings are done in the TCAE GUI. A cartesian block mesh is created as an initial background mesh, which is further refined along with the simulated object.

The CFD simulation is managed with TCAE software module TCFD, which uses OpenFOAM open-source application. The simulation setup includes parameters such as simulation type, time management, physical model, and turbulence model.

The TCAE simulation run is completely automated, and the whole workflow can be run by a single click in the GUI or in the batch mode on a background. The simulation is executed in the steady-state mode, and the software includes a built-in post-processing module that evaluates all the required quantities.

The results of the simulation can be animated, showing the rotating axial fan and the deformation of the impeller due to inertia and axial forces and forces from the airflow. The speed of rotation is approximately 1200 times slower than the real rotation, and the deformation movement is displayed 200 times higher to enhance the details.

Here's a summary of the parameters used in the simulation setup:

For FEA setup, you'll want to create a simple, single, closed STL surface of the axial impeller solid. This has already been done for us in the design stage, but if you're starting from scratch, make sure to remove any tiny, irrelevant, or problematic model parts and seal up any holes to create a watertight surface model.

The computational mesh for FEA is created using the NetGen open-source application in the TMESH software module. The most important parameters for FEA meshing are "h Max" and "h Min", which determine the maximal and minimal mesh edge in meters.

You'll need to set these parameters in the TCAE GUI, which is where you'll also manage the FEA simulation setup and run. The TFEA software module uses the Calculix open-source application to handle the simulation.

In the TFEA GUI, you'll want to specify the material properties, such as beam material (steel), material density (7800 kg/m3), and Poisson ratio (0.3). You'll also need to set the fixed radius (100 mm) and finite element order (second).

Here's a summary of the key material properties you'll need to set:

The Results and Visualization section is where we get to see the axial fan design in action. The animation shows the rotating axial fan and the deformation of the impeller due to inertia and axial forces, as well as forces from the airflow.

The speed of rotation in the animation is approximately 1200 times slower than the real rotation, which helps to give us a better understanding of the design's dynamics.

The deformation movement in the animation is displayed 200 times higher to enhance the details, allowing us to see the intricate movements of the impeller.

Axial fan design requires careful consideration of the fan's size and shape to achieve optimal airflow.

A larger diameter fan can move more air, but it also increases the fan's weight and makes it more difficult to install.

In axial fan design, the fan's hub is typically located at the center of the fan, which helps to reduce vibrations and improve stability.

The fan's blade angle and pitch can also impact airflow, with a more aggressive angle resulting in higher airflow rates.

Axial fans are often used in applications where a high airflow rate is required, such as in computer cooling systems.

In axial fan design, the fan's motor is typically located at the hub, which helps to reduce noise levels and improve efficiency.

The fan's casing and inlet/outlet design can also impact airflow, with a well-designed casing helping to reduce turbulence and improve airflow rates.

A well-balanced axial fan is essential for optimal performance, with even the slightest imbalance affecting airflow rates.

The axial fan design process relies heavily on precise calculations to achieve optimal performance.

Calculations for fan design involve determining the fan's diameter, blade angle, and airflow rate, all of which can be determined using formulas from the fan design process.

To calculate the fan's airflow rate, you can use the formula Q = π × D² × N × C, where Q is the airflow rate, π is a mathematical constant, D is the fan's diameter, N is the number of blades, and C is the blade angle.

Expand your knowledge: C Purlins Roof Design

The fan calculator is designed to help you find a suitable product for your application, but it's not meant to design a fan from scratch.

Selecting the correct values for inlet and outlet pressures can be a challenge.

The static pressure in the fan, denoted as ps, is the maximum of the inlet and outlet pressure.

You'll also need to consider the pressure head of the gas at the outlet side of the fan, represented by h.

Getting these values right will give you the most accurate results from the fan calculator.

The fan calculator calculates the airflow through an impeller, taking into account the effects of a restricted casing diffuser.

Common Data is where things get specific, and you need to know the right values to get accurate results.

The acceleration due to gravity, g, is a crucial value that must be set to 1 if you're working with units of mass per unit area, such as kgf/m² or lbf/ft².

You may be wondering why this is the case, but essentially, it's a mathematical requirement to ensure your calculations are accurate.

If you're not interested in determining the gas-change rate, you can ignore the volume of a room or space, V, altogether.

However, if you do need to calculate the gas-change rate, V is a vital piece of information that will help you get the right answer.

When it comes to the fan's power, P, you'll want to make sure you're using the minimum power required, usually measured in Watts.

You can also account for losses in the fan's efficiency, ε, by multiplying the expected losses by the efficiency factor and entering the modified value in the input data.

For more insights, see: Gas Stove