Mass Flow for 2D
 

Hi all,

I have mass flow rate at Inlet. But it is for actual geometry. For solving 2D problem, I have to take the same mass flow rate or different one.

Can anybody suggests.

Thanks in advance.

Mahesh

Re: Mass Flow for 2D
 

If you're using the 2D solver (not Axi), FLUENT uses a third virtual dimension which is 1 meter long to do calculations.

So, if you want the same flux (kg/(m^2 s)) through your system, you need to change inlet mass flow rate. Just divide your actual mass flow rate by the actual inlet section and then multiply the result by the model section, which is given by the inlet width multiplied by 1 m.

Hope this helps

Hi

ap

Re: Mass Flow for 2D
 

hi,

Then in that case my mass flux will be more than the actual( as 3rd dimension is 1m). But I have only 2D c/s & dont know about the area. Then how to proceed?

Thanks.

Mahesh

Re: Mass Flow for 2D
 

Hi mahesh

u have to divide your original mass flow rate [for example: in Kg/s] by the section area of your inlet section. Your unit becomes [Kg /(m²s)]for example. Then, ucompute the area of the virtual section [m²] (multily the edge length on your 2D geometry by 1 m); and u multiplye it by the mass flow rate :

[(Kg /(m²s))* m²]=[Kg /s]

Sorry for my english,

Good Luck

Re: Mass Flow for 2D
 

Your mass flux (kg/(m^2 s)) stays constant. What changes is the mass flow rate (kg/s).

Call G the mass flux, m_a the actual mass flow rate, Sa the actual section, L the lenght of the edge of your inlet in the 2D model. You have:

G = m_s/S

The mass flow rate you have to use in the model is:

m_model = G * L * 1 m

Hi

ap

Re: Mass Flow for 2D
 

Dear ap,

We have completed trial runs on a 2D geometry. We are facing following problems,

When we keep mass flux same i.e when we impose mass-flux at inlet and pressure at outlet, we are getting very high pressure values at inlet.On the other hand when we give pressure in and pressure outlet bc, we get very less mass flux.

So, exactly what we should look for in 2D analysis, mass flux ? or pressure ?

Thanks, Mahesh

Re: Mass Flow for 2D
 

If you are really unsure of what the 2D solver is giving you, you could just extrude the 2D mesh a unit distance (keeping cell aspect ratios in mind) and then apply symmetry boundaries on the sides. This should be numerically identical to a 2D calculation.

Thanks a lot guys..I have the same problem. I was looking for solution..this thread really helped.

Hi Friends,
i am simulating an ogee spillway with Fluent 2D, i am going to verify my CFD model with experiment model with 1/50 scale of prototype. Froude number is used for similarity and based on that the 6000cms in real become 0.34cms in model (6000*(1/50)^2.5=0.34). the spillway is 68meter in reality and become 68*(1/50)=1.36 meter in model.
as i am modelling it 2D do i have to divide 0.34*998.2 to 1.36 to get the correct massflow rate in my model (which become 0.25*998.2)? (i have used massflow rate as inlet)

every help will be appreciated.