Fan rotor region simulation

[jake]

Hi,

I am simulating a mixed flow fan using rotor region approach, however, the results for pressure and flow rates are not match with the test results. I followed all instructions published in Autodesk website for rotor region (Turbomachinery) CFD simulation.

Please advice me how to solve the issue?

Kind Regards,

Shaun Houreh

[karol.suchon]

Please attach the model and the test results. 
Sometimes that is a matter of simulation time, sometimes that is a matter of postprocessing.

Your results do not have a constant value but they are changed over time, so you could pick them for comparison the pick of the pressure or volume flow rate.
BR
Karol

[jake]

Hi BR Karol,

Thanks for your reply.

Please download CFD files for the fan simulation in the following link:

https://www.dropbox.com/s/6lpg1972ydb0m3j/RMC-400-600LS.zip?dl=0

CFD shows the pressure different of 200 Pa for 600l/s flow rate, but the actual one is 360 Pa.

Please help to fix it.

Kind Regards

Shaun Houreh,

Senior Mechanical Engineer

EA ID: 5147917

[karol.suchon]

Hello Shaun,

I have a problem with reopening the model, could you attach the support file or create the shareable file?

BR
Karol

[jake]

Hi Karol,

Please see the support file as requested.

Let me know if you need more information.

Kind Regards,

Shaun Houreh

[karol.suchon]

I changed a mesh to a manual but the source of the issue is much more simple. 
It is better to have a volume flow rate on the inlet and the pressure on the outlet. 
After the change, I got around 360-380 Pa difference between the sides.

BR
Karol

[jake]

Hi Karol,

Thanks for your support.

However, as you can see in the screenshot, the flow direction is reverse!

Flow comes from outlet to inlet. This is a fan and consumes the power to suck airflow from inlet (smaller area) to outlet (larger area).

Can you please have a look at your simulation to confirm? 

Regards,

Shaun

[jake]

In the other word, we need to make sure it is working as a fan (absorbing power) not wind turbine (generating power).

[karol.suchon]

Jake,

I do not look into the definition of VFR only to the error of direction 😞

I will try to rerun the simulation in the proper direction.

BR
Karol

[jake]

Thanks.

360 Pa pressure difference is expected for 1400rpm.

For 1250 rpm, 287 Pa is ok.

inlet needs to be low pressure, outlet high pressure as this is a fan.

Regards,

Shaun

[jake]

Karol,

How Autodesk CFD distinguish the Fan is absorbing power or generating?

[karol.suchon]

I give up on the pure free flow and create the inlet pipe.
We get some additional pressure difference generated by the decrease in the hydraulic diameter of the flow( from a big square to a small cylindrical hole).

I get around 310 Pa difference, but I think that during the time the difference could be a little smaller. The average pressure increases a little during the simulation. I will run a few more iterations and will let you know.

You could compute the power using torque in rotating region results but that is only a sign and need to be compared to the direction of the rotation.

BR
Karol

[jake]

Hey Karol,

Any update on this?

Thanks,

Shaun

[karol.suchon]

After another few rotations, the results are the same.

BTW, how does the test look in the real world, Do we have the inlet as a pipe, or it is the same as you draw?

BR
Karol

[jake]

The real test has been done according to ISO 5801 – Installation type A. it means inlet chamber and outlet chamber

Fan pressure 363 @1397 rpm for 600 l/s.

Do what method CFD needs.

I can send 3D geometry of Fan too.

[karol.suchon]

Ok, so I need back to the original geometry.
I will try to refine the mesh and run the simulation once again.