Learning Forum

[raju.chowdhury]

Hi,

I am simulating gas flow through multi-nozzle towards a liquid pool using the symmetry boundary condition. In this simulation, nozzle exit is using as inlet and I am using velocity inlet boundary condition. My nozzle exit velocity is 300 m/s. As I have sliced the whole geometry into two parts, each part contains  two complete nozzle and 2 half nozzle. My query is, for symmetry case what would be the velocity at half nozzle exit? 150 m/s or 300 m/s? As the nozzle is half so the velocity should be 150 m/s. But when I will visualize the full nozzle using the mirror/reflect, nozzle velocity will remain the same (150 m/s) which is not expected (because when I will see the full nozzle, I also expect the nozzle exit velocity 300 m/s).

I will be pleased if clarify my question in details.

[Amine Ben Hadj Ali]

What are you using at outlet? Does the inlet velocity or mass flow correspond to half geometry? Is the flow symmetric? Geometrical symmetry does not mean flow is symmetric.

[raju.chowdhury]

At outlet, Pressure outlet boundary condition have been used. Inlet velocity corresponds the half geometry and the flow is symmetric.

[Karthik Remella]

As mentioned by my colleague, using symmetry does not change the flow rate or velocity by half. You will need to use the original flow rate in this case.

Just to add - Symmetry simply means that:

• normal velocity at the plane of symmetry is 0.


• normal flux at this plane is 0.

Best,

Karthik

[raju.chowdhury]

Hi Karthik,

 

Thanks for your reply.

If I use original velocity at half geometry then mass flow will vary between full nozzle and half nozzle as area are not same (full nozzles area is 3 m^2 whereas half nozzle area is 1.5 m^2). So, how can I ensure the same mass flow at each nozzle exit?

 

[Amine Ben Hadj Ali]

You cannot ensure that. You need to run full or rely on the velocities.