'Analysis of fan variants' simulation project by sjesu_rajendra


#1

I created a new simulation project called 'Analysis of fan variants':

Simulations comparing 2 variants of fans and the corresponding flow. The geometry was provided by Friendship Systems - CAESES.


More of my public projects can be found here.


#2

Description


In the past few decades, turbomachines have found a variety of applications in a wide range of industries. A turbomachine could be something as simple as the fan on the top of your table to something as complex as the gas turbine of an air-breathing jet engine. Essentially, a turbomachine is a mechanical device used to alter the velocity and pressure of the fluid passing through it. In this project, we are going to deal with how to computationally analyze turbomachines in order to achieve desired outcomes.
 
In our case, to keep it simple, we choose to work with fans. Usually, a fan is used to create a pressure drop in the working fluid. The design of a fan comprises of various components viz. direction of fluid flow, no of blades, orientation of blades etc. Since we’re only getting started, let’s consider two similar fans with a different blade profile.

Project Goals


Through this project we intend to achieve the following:
· Simulate the effect of 2 fans with different blade profiles
· Investigate the results of each fan to analyze components, such as streamline contours, velocity, pressure etc.
· Perform a comparative study of both the fan systems. This helps us determine the more efficient design.
 
Here, we define efficiency as the ratio of the output velocity of the air to input power of the fan.

Geometry


The geometry of the fans was created with the help of CAESES, a design platform that offers simulation-ready CAD models.
 
Below, you can have a look at both our fan profiles to gain a better idea of what we’re dealing with:
 
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Fan profile 1
 
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Fan profile 2
 
As you may have noticed, the blades of Fan 2 have a greater radius of curvature than Fan 1. Although, all the other parameters are the same:
· No of blades= 6
· Direction of fluid flow: Axial
 
Moreover, in both cases, we use a cylindrical cell zone that contains the fan and a significant amount of air surrounding it. A cell zone is a region which encompasses threads of cells that are defined by certain parameters. In our system, the cell zone is defined by a rotational velocity. As shown in the image, the cylinder in grey is the selected cell zone region.
 
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Cell zone region

Meshes


Meshing is an integral part of simulation. Fundamentally, it is the process of uniformly dividing the body under study into a multitude of small, finite elements. Analyzing the effects on each of these elements separately and then combining them gives us a more accurate collective result.
 
To perform the meshing, both of these geometries need to be imported onto the SimScale platform. This could be done by converting the CAD documents to neutral file formats, such as STEP, IGES, PARASOLID etc.
 
For this task, we will use hex-dominant parametric meshing. This mesh type is most suitable to deal with cell zone conditions.
 
After meshing operation, the mesh will appear as shown below:
 


 
Mesh mapped onto fan geometry
 
A finer element of the mesh leads to a higher order of accuracy in the result. If the mesh is too fine, then the computational time will be higher. Consequently, we need to find just the right balance of fineness and ease of computing in order to optimize our result. In our simulation, the system is most dynamic in the cell zone region. As a result, we can observe in the image below that the mesh gets finer in proximity to the fan.
 

 
Mesh refinement
 
To simulate the airflow across the fan, we consider the fan to be enclosed in an imaginary wind tunnel. This would be the scope of our study and any effects outside the box would be ruled out.
 

 
Meshed enclosure

Simulations


The fluid, being air, is chosen to be incompressible and the selected turbulence model is k-omega SST. Since we are using cell zone conditions, a steady state system is adopted.
 
A simulation is run subsequent to inputting boundary conditions on the system. Basically, a boundary condition is an equation that defines the constraints of the problem. In our case, the boundary conditions are the same for both the fans and the input velocity of the air is equal to 4 m/s.
 
A pictorial representation of the simulation can be observed in the figure below:
 


 
Schematic of the simulation

Results and Conclusions


After the simulation run, we see the post-processing images to determine the better system.
 
The pressure contours of the simulation can be represented as follows:
 
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Pressure contours: Fan 1
 
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Pressure contours: Fan 2
 
From the two pressure contours, we can observe that a greater pressure drop is generated by Fan 2 as compared to Fan 1.
 
As explained earlier, the purpose of a fan is to create a pressure drop in the working fluid. Since Fan 2 has a greater pressure drop, we can say that it serves a fan’s purpose to a greater extent.
 
As another approach, we could consider the velocity contours:
 
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Velocity contours: Fan 1
 
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Velocity contours: Fan 2
 
From the velocity contours, we observe that the outlet velocity is higher for Fan 2. Numerically, the outlet velocities are compared and it is found that Fan two 2 achieves a higher velocity of air for the same input power. As a result, it can be said to be the more efficient system. Thus, we would choose Fan 2, i.e., a fan with blades of a higher radius of curvature for desired applications.
 
The streamlines around one of the fan variants are shown below:
 


 
Velocity streamlines around Fan 1
 
More interesting results such as the forces exerted on the fan, velocities, pressure etc., can be obtained from the post-processing tab of this project. Happy Simulating! :smiley: