[Anandltvs]

Hi,

From CFD simulation of 294 frame axial flow fan, i got fan performance as 22.95% at P=100.3 Pa,Q=582 m3/hr,2863 RPM.But the same fan during the air flow test provides fan efficiency as 42.20% at P=100.72 Pa,Q=1157 m3/hr,2879 RPM.Both operating points are same, but cfd predict around 50% less flow rate than test. What would have gone wrong in the simulation? kindly seek your help to address this issue. For your reference
CFD Setup info:
1. Physics: In compressibility flow
2. Analysis type: transient
3. Approach: Frozen rotor
4. Convergence ratio: 0.0001
5. Turbulence Model: K- epsilon
6. Fan and chamber considered(Shroud ignored)
7. Boundary layer: Single layer used
Test info:
1.Air flow test chamber-According to ANSI/AMCA 210-07
2.Fan-Shroud and Chamber used in test
( Shroud ignored in CFD we have got good correlation between test and CFD other frames of fan(350 mm,370 mm) but in this frame 294 mm i am getting unreasonable correlation of 50% in CFD.)


Thus, I could see my CFD simulation has failed to capture large flow generated by fan in the test. How to capture resonable flow prediction in CFD simulation. I used AutodeskCFD2012 for this simulation.

Regards
Anand madeshwaran

[koray]

Hey,

Do you have shroud in your tests and not in your CFD simulations? If so, you can't expect the same results. Tip clearance has a huge effect on the fan performance.

You should work on the cells in the boundary layer, one layer is insufficient even if you use SWF. Have you checked y+ value at the end of your simulation?

I suspect you are using an automatized software for simulation. You can also, try using more advanced software in case you have appropriate background in CFD.

Hope you'll solve it soon.

Cheers,
Koray

[Anandltvs]

Mr.Koray,

Thanks for your comments. Yes, Like you. i also suspect the shroud.At present, i am trying to include shroud in my CFD setup.I used autodeskCFD for this simulation.But my big doubt is how could i can get good correlations for other fans(305,350, and 370 fans) without including shroud in the CFD simulation? What will be the recommenced Y+ and boundary layers settings for axial fans(car radiator application). For this case, Will you recommend CFX with ICEM CFD or AutodeskCFD ?

[jpando]

Originally Posted by Anandltvs

Mr.Koray,

Thanks for your comments. Yes, Like you. i also suspect the shroud.At present, i am trying to include shroud in my CFD setup.I used autodeskCFD for this simulation.But my big doubt is how could i can get good correlations for other fans(305,350, and 370 fans) without including shroud in the CFD simulation? What will be the recommenced Y+ and boundary layers settings for axial fans(car radiator application). For this case, Will you recommend CFX with ICEM CFD or AutodeskCFD ?

I would recommend using a Y+ = 1 with the enhanced wall functions. You will want to make sure you grow your layers to cover the boundary layer height.

I use ICEM CFD for mesh generation because it has a large range of functionality. With enough experience in it, you can do pretty much anything.

[Anandltvs]

Thanks Mr.Jpando. Your hint at boundary layer and ICEM CFD will help me a lot.

Regards

Anand

[koray]

Originally Posted by Anandltvs

Mr.Koray,

Thanks for your comments. Yes, Like you. i also suspect the shroud.At present, i am trying to include shroud in my CFD setup.I used autodeskCFD for this simulation.But my big doubt is how could i can get good correlations for other fans(305,350, and 370 fans) without including shroud in the CFD simulation? What will be the recommenced Y+ and boundary layers settings for axial fans(car radiator application). For this case, Will you recommend CFX with ICEM CFD or AutodeskCFD ?

Hey there,

You should always take shroud into account, it's essential in this problem. Autodesk CFD is the new CF Design. As far as I know, you can't have much freedom and flexibility in creating mesh in Autodesk CFD while you have full control in ICEM CFD. When it comes to turbulence modelling and basic algorithms that these two software use, it's not much different. But still, CFX, has some advanced tools just for turbomachinery industry. If you have the chance to use CFX&ICEM CFD and enough time to learn them then, pick them.

Cheers,
Koray