centrifugal fan/pump simulation

mariashva · May 23, 2018, 22:35

I'm currently working on a simulation case with multiple centrifugal fans in a system to blow the air. I have a few questions:

1. Regarding the static pressure in a centrifugal fan curve, what does it represent? For axial fans it is very straight forward because I can simply use a 2D surface as the fan and the pressure difference between two sides of the surface would be the static pressure. Since centrifugal fan has separate inlet and outlet surface, then what's the definition of the static pressure?

2. I want to simulate centrifugal fans without considering the blades. If I know the fan curve, then generally how to set up the BCs for the model? Thanks for your help

LuckyTran · May 23, 2018, 23:03

The static pressure rise is the same as the pressure difference. It is quite literally the actual static pressure rise across the fan. The difference with a centrifugal fan is its geometry. But if you plan to not modeling the fan, you can still use a 2D surface just like an axial fan because the flow does not need to know whether it came from an axial or centrifugal fan.

There is a fan boundary condition that lets you put in a polynomial for the pressure jump, which lets you put the fan curve as a BC.

mariashva · May 23, 2018, 23:11

Thanks for your reply. For centrifugal fan, what I understand about the static pressure is the pressure difference between the inlet and the radial outlet, is this right?

You mean I can still use a 2D surface as the centrifugal fan for simulation? but since the geometry has a inlet and outlet, so do I just set the inlet as the fan BC and the outlet as interior? I guess this may not be accurate because the static pressure in this case is different from the static pressure definition from a centrifugal fan.

LuckyTran · May 23, 2018, 23:26

Just leave out the fan, you don't need it. If you needed it, you'd model the impellers too.

mariashva · May 29, 2018, 15:19

Really thanks for your help. I am still curious about a few things here.

1. if I only use a 2d surface as the centrifugal fan, how to choose the surface? like for a 3D centrifugal fan, how to choose a 2d surface to accurately reflect the flow through a centrifugal fan?

2. About the static pressure of a centrifugal fan, if I consider it as a 3D fan model with a n inlet and an outlet, does the static pressure mean the pressure difference between the inlet surface and the outlet surface? or simply just the pressure different between the 2 sides of the inlet surface (or outlet surface)?

kiran · May 30, 2018, 09:07

I suggest you to use 3D centrifugal fan model, with MRF modelling, If you know the RPM.

Since you told there are many such fans in the system, the accumulation/combination effects of all them is very much important. This isnt possible in 2D Case.

IF you really want to do 2D modelling for the fan, then too many factors are to considered.

mariashva · May 30, 2018, 14:08

Hi Kiran, thanks for your help. I have no prior experience in MRF modelling, and I thought I can go with a easier model if I already have the fan curve from the manufacturer which I can directly use in the model. I guess I need to have the exact impeller shape for MRF model is that right?
By the way, could you elaborate more on the 2D modelling of centrifugal fan in this case? Thanks for your help.

May 23, 2018, 22:35	centrifugal fan/pump simulation	#1
mariashva New Member Ray Join Date: Mar 2014 Posts: 20 Rep Power: 12	I'm currently working on a simulation case with multiple centrifugal fans in a system to blow the air. I have a few questions: 1. Regarding the static pressure in a centrifugal fan curve, what does it represent? For axial fans it is very straight forward because I can simply use a 2D surface as the fan and the pressure difference between two sides of the surface would be the static pressure. Since centrifugal fan has separate inlet and outlet surface, then what's the definition of the static pressure? 2. I want to simulate centrifugal fans without considering the blades. If I know the fan curve, then generally how to set up the BCs for the model? Thanks for your help

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May 23, 2018, 23:03		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	The static pressure rise is the same as the pressure difference. It is quite literally the actual static pressure rise across the fan. The difference with a centrifugal fan is its geometry. But if you plan to not modeling the fan, you can still use a 2D surface just like an axial fan because the flow does not need to know whether it came from an axial or centrifugal fan. There is a fan boundary condition that lets you put in a polynomial for the pressure jump, which lets you put the fan curve as a BC.

May 23, 2018, 23:11		#3
mariashva New Member Ray Join Date: Mar 2014 Posts: 20 Rep Power: 12	Thanks for your reply. For centrifugal fan, what I understand about the static pressure is the pressure difference between the inlet and the radial outlet, is this right? You mean I can still use a 2D surface as the centrifugal fan for simulation? but since the geometry has a inlet and outlet, so do I just set the inlet as the fan BC and the outlet as interior? I guess this may not be accurate because the static pressure in this case is different from the static pressure definition from a centrifugal fan.

May 23, 2018, 23:26		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	Just leave out the fan, you don't need it. If you needed it, you'd model the impellers too.

May 29, 2018, 15:19		#5
mariashva New Member Ray Join Date: Mar 2014 Posts: 20 Rep Power: 12	Really thanks for your help. I am still curious about a few things here. 1. if I only use a 2d surface as the centrifugal fan, how to choose the surface? like for a 3D centrifugal fan, how to choose a 2d surface to accurately reflect the flow through a centrifugal fan? 2. About the static pressure of a centrifugal fan, if I consider it as a 3D fan model with a n inlet and an outlet, does the static pressure mean the pressure difference between the inlet surface and the outlet surface? or simply just the pressure different between the 2 sides of the inlet surface (or outlet surface)?

May 30, 2018, 09:07		#6
kiran Member kiran Ambilpur Join Date: Jun 2010 Location: India Posts: 50 Rep Power: 16	I suggest you to use 3D centrifugal fan model, with MRF modelling, If you know the RPM. Since you told there are many such fans in the system, the accumulation/combination effects of all them is very much important. This isnt possible in 2D Case. IF you really want to do 2D modelling for the fan, then too many factors are to considered.

May 30, 2018, 14:08		#7
mariashva New Member Ray Join Date: Mar 2014 Posts: 20 Rep Power: 12	Hi Kiran, thanks for your help. I have no prior experience in MRF modelling, and I thought I can go with a easier model if I already have the fan curve from the manufacturer which I can directly use in the model. I guess I need to have the exact impeller shape for MRF model is that right? By the way, could you elaborate more on the 2D modelling of centrifugal fan in this case? Thanks for your help.