Learning Forum

[egozukara]

I am currently working on a simulation for axial flow fans that I aim to validate using actual values. While I have made some progress, I am uncertain about the accuracy of our setup. Can you help with geometry cleaning, mesh operations, fluid domain preparation, and especially your suggestions about the setup and the places you see critical? I try everything but I get differences with the actual values and this difference changes at different volume flow rates. I am using the MRF-RANS technique. I am using tube geometry for the outlet. I am not sure what the diameter of this output tube should be. I look forward to your feedback.

[Federico]

We can provide suggestions on this Forum based on specific questions and/or the information you can provide us. We cannot access files or provide 1-on-1 support.

[egozukara]

I see. So what is the effect of the outlet diameter of the tube-fluid domain created in MRF-RANS fan simulations on the analysis? What would you suggest to me to make the ratio between this tunnel exit diameter and fan diameter? Does the growth of this diameter cause losses in the analysis? I am waiting for your suggestions, thank you.

[egozukara]

 

 

 

[Rob]

Rather than ask about domain size; what is the experimental domain size?

[egozukara]

The outlet diameter of the wind tunnel where I did the tests is 940mm and the fan diameter is 400mm. When I simulate with the actual wind tunnel diameters, I get results that are far from the actual values, but when I change the outlet diameter, these results vary. What do you think could be the reason for this, what should this ratio be?  

[Rob]

And what are the boundary conditions in the tunnel?

[egozukara]

The wind tunnel is designed according to the AMCA-210-16 standards. The fan is installed at the inlet of the tunnel, and measurements are taken from the tunnel walls using multiple probes positioned at the 480 mm mark on the z-axis. The measurements are conducted at ambient atmospheric pressure. The fan operates at variable RPM, such as 3000 RPM. At the exit of the air tunnel, I use another fan to adjust the static pressure (for ex.50 Pa), bringing it to the desired level of 480 mm. This setup allows me to observe how the fan generates a flow rate under different pressure values and rotational speeds.

 

[Rob]

And how does that compare to the boundary settings used in Fluent? What material properties did you use? 

[egozukara]

 

I calculate the air density according to the temperature and humidity measurements I took before the test and assign it to Fluent. I assign a slip condition to the walls to eliminate friction losses in the wall and tunnel material. I assign 0Pa guage pressure-inlet to Fluent for the inlet and the 0pa outlet. I assign the actual rpm value I read in the test to the mrf region I set in Fluent. I get mass flow rate and pressure at 480mm as output.

 

 

[Rob]

How well resolved is the mesh? Does the CFD pressure field vary near the monitor points? 

[egozukara]

I checked the mesh quality, and it is okay. I also checked the solution monitors for pressure and mass flow, and they are stable.

[Rob]

How do the various results contours look? 

[egozukara]

I checked pressure and velocity contours, as well as 2D and 3D streamlines. The flow is affected by sudden expansion as the outlet tunnel diameter increases, but I don't know what the tunnel diameter at the outlet will be. 

[Rob]

If changing the outlet diameter changes the results, and you don't know what size the outlet is how can you compare with experimental data? Sharing the images would also help: my crystal ball is off for repairs. 

[egozukara]

Thank you for your assistance. I appreciate your efforts to help, but I'm finding it challenging to communicate my issue through messages. I would like to explain my situation in more detail so we can work towards a solution. It would be much more effective if we could arrange a meeting to discuss this further.

[Rob]

Which I am unable to do. Commercial users with the correct licences can contact us (or a Partner) for that level of support, otherwise, I can only respond to information on the Forum.