[sankeerth2292]

Hi,

Please help me out! Iam doing a CFD modelling of Vortex tube in Fluent. Iam a beginner to CFD.


Regards,
Sankeerth

[R4RAHUL]

what type of help you need? what you want to know about cfd?

[sankeerth2292]

Originally Posted by R4RAHUL

what type of help you need? what you want to know about cfd?

Iam doing a project in Vortex Tube. I want to model the flow. To do that how should the mesh be?(any advice on this would really be good) And how do i mesh manually in Ansys Mesh. Iam using Workbench Interface for solving in Fluent.

Any help in this regard is much appreciated.

Thank you in advance

[sankeerth2292]

Originally Posted by sankeerth2292

Iam doing a project in Vortex Tube. I want to model the flow. To do that how should the mesh be?(any advice on this would really be good) And how do i mesh manually in Ansys Mesh. Iam using Workbench Interface for solving in Fluent.

Any help in this regard is much appreciated.

Thank you in advance

While trying to model the flow, I obtained Divergence in AMG Solver: Pressure Correction. My BCs were inlet pressure at 9atm or 911925 Pascal(absolute pressure) and inlet Temp=300 K
and At outlets i have considered that gauge pressures are zero.

[R4RAHUL]

just decrease your under relaxation factor and then try again

[sankeerth2292]

Iam not able to generate the temperature difference no matter how many times i try. I tried simulating in Solidworks and Fluent , was completely unsuccessful in my attempt to obtain results.
Can anyone please what might be the reason for this?

[fluid23]

You probably have a mesh issue if you are a beginner. That can cause all kinds of issues. You really aren't giving us enough information to help you. What does your mesh look like? What kind of turbulence model are you using? What are your initial conditions? These are all things that you should try to communicate when you ask for help.

[sankeerth2292]

Dimensions of the model:
Inlet Dia: 4mm
Vortex Tube Dia= 2.5mm
Cold tube dia = 0.84mm
Length of Vortex tube= 125mm

Model: Standard k-e Turbuence model
Solver type: Steady, Pressure based
Fluid: Air(Ideal gas)

Boundary Conditions:
Inlet Pressure= 601325 Pa
Outlet Pressure Cold = 101325 Pa
Outlet Pressure Hot = 101325 Pa
Operating Conditions Pressure= 0 Pa

Turbulent Parameters:
Turbulent Intensity= 10%
Hydraulic Diameters at each Cross-section have been given as input in

Hybrid Initialization has been done

Meshing Details

Sizing: On proximity and curvature
Initially assembly meshing was not at all used but i found very poor quality of elements were being formed, then i tried with assembly meshing there was good increase in quality

Assembly Meshing(Cutcell) has been done to improve element quality

Attached is the mesh image

can initialization of the model influence the convergence ability?
How do we modify the mesh if it's not proper(I mean should we go by trial and error only)?

[fluid23]

Is this your whole domain? Can you show a cut through the middle that shows what the mesh looks like inside? Unfortunately, it is tough to tell much from looking at the outside surfaces.

[fluid23]

There are several ways to check if your mesh is adequate. The most important being y+, but also quality, skewness, volume change and aspect ratio. Ask someone in the Fluent forum how to proceed with that if you are unsure. I use different software so I can't really help you on that. This isn't really the right forum for such a discussion anyway.

http://www.cfd-online.com/Forums/fluent/

[sankeerth2292]

Here are some mesh images that i have taken .
May I know what software are you using and what is meant by "y+"?

mesh1.jpg

mesh2.jpg

mesh3.jpg

mesh4.jpg

mesh5.jpg

[sankeerth2292]

Other Mesh images are attached here

Is this mesh fine? If not how do you suggest i mesh the part?

[fluid23]

Is this gray thig a fluid or a solid? I am confused. You should be meshing the fluid around your object, not the object itself. Unless you are solving for heat transfer, then you will need the solids too.

As for wall Y+, check the wiki on this site for details. It is a fundamental aspect of CFD and if you are ignoring it you are in for all kinds of trouble. Basically it is a measure of how appropriate your boundary layer mesh is for the local flow conditions. There is more to it than that, but you should really figure that out for yourself.

I use star-ccm+.

[sankeerth2292]

The Gray thing is the fluid volume extracted from the solid model(solid model has been made in solidworks).

The meshed & extracted fluid volume has been shown in the pictures

[fluid23]

In that case it looks like you need to add bounday layer refinement. I would bet that is why you are seeing divergence. Your cells near the wall are too big for the near wall calculations (i.e. your y+ is too big). I am not sure what options your software has available so I would HIGHLY recommend going and getting help in the Fluent forum (link posted above).