Mass flow rate in DPM
 

Hi.

I use a single point injection in a axisymmetrical case. In the Fluent Help it says that the mass flow rate is defined per 2*PI radians. I interpret this as if I have a total mass flow of say 2kg/sec, then I should write the mass flow rate as 2/(2*PI)=0.318kg/sec in the panel.

But when I try to summarise the DPM phase in report/volume integrals/sum then I just get 0.318kg/sec instead of 2kg/sec. Clearly I have misinterpreted something. Can anyone help ?

Cheers Christian

Re: Mass flow rate in DPM
 

I think you should define the mas flow rate as 2kg/s directly.

guohuiwang

Re: Mass flow rate in DPM
 

Hi christian

when you use an axisymetric grid, the "depht" of the volume is equal to 1 radian.

So if you inject particle you have to divide the real massflow by 2 PI in order to have the correct mass, momemtum and heat source from DPM.

Of course when you use integral value in the report you should multiply these values by 2 PI because FLUENT give you the integral value on a 1 radian slice.

I think it might be possible to change this depth in the reference value panel.

Best regards

Alain

Re: Mass flow rate in DPM
 

Thats what I would like to do, but is the manual incorrect then ?

Cheers Christian

Re: Mass flow rate in DPM
 

Hi.

When I in the report\volume integrals choose volume, Fluent calculate the correct total volume and not the volume per 2*PI even though Fluent says that: "The volume of a surface is computed by summing the volumes of the cells that comprise the zone". Fluent then knows that because this case is axisymm. It can calculate a volume based upon a 2D model.

I then choose the field variable as DPM and option: Sum. Now I would expect that because Fluent says: "The sum of a specified field variable in a cell zone is computed by summing the value of the selected variable at each cell in the selected zone" it still is based upon the correct volume and not on volume per 2*PI.

But as I have mentioned I the previous mail, the manual clearly says that the mass flow rate input should be based per 2*PI.

I am still confused how to interpret these inputs and outputs. Especially because when I in the input use the total mass flow and not mass flow per 2*PI, the result looks as expected.

Cheers Christian

Re: Mass flow rate in DPM
 

1. Guohui's answer is correct. Concept of DPM injection is based on point injection. The concept of '2*PI' is for continuos phase(gas phase), not for DPM.

2. Fluent 4.5 have used 1 radian, not 2*PI radian.

Sincerely, Jinwook

Re: Mass flow rate in DPM
 

Hi Guohui, Jinwook and Alain.

Thank you for your time and answers. It has been helpful.

Cheers Christian

Mass flow rate in DPM
 

Hi Christian,
I am also facing the same problem with 2D axisymmetric case. Can you tell what values you finally interpreted, i.e., should be divided by (2 'Pi') or total flow rate for whole volume? :)

Mass flow rate in DPM regarding
 

Hi all,
I am also facing the same problem with the 2D axisymmetric case. Can you tell what values you finally found out whether it should be divided by (2 'Pi') or total flow rate for whole volume?

Thanks in advance.