Ansys Fluent

| 15-09-2021
[RAND-1-100] Comments

in Fluids
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I am doing a counter-flow heat exchanger simulation in ANSYS student version.

After I setup, I always got error 'floating point exception' in calculation.

ANSYS FLUENT software contains the broad physical modeling capabilities needed to model flow, turbulence, heat transfer, and reactions for industrial applications ranging from air flow over an aircraft wing to combustion in a furnace, from bubble columns to oil platforms, from blood flow to semiconductor manufacturing, and from clean room. ANSYS Fluent is part of the ANSYS suite of engineering analysis software, which includes Mechanical APDL, BladeGen, and many other software packages capable of thermal analysis, electromagnetic analysis, and more. Fluent is also widely recognized as one of the industry standard CFD software packages. Although Solidworks is capable of performing.

Please can somebody solve my problem?

Intialization result:

Ansys Fluent User Guide

n

During calculation:

Error:

There are my all the details:

Details:

It is recirculated exhaust gas heat exchanger which used in gas turbine. It is 200mm long with 60mm diameter.

In my geometry, this heat exchanger consists of three parts, hot air fluid domain (outer domain) , 4 solid pipes and 4 inner fluid domain (2 methane and 2 air). As you can see, there are 8 interfaces in total.

This is my meshing. I used adaptive sizing function to get less cells (119610 nodes and 326512 elements). And 4 edge sizing for pipes (20 Division hard). I don't use culvature size function because it will lead to 3300000 elements which I can't run it in student version.

This is my skewness data.

However, in my setup part. There are my setting.

Pressure-based

Absolute

Steady

Density on Y direction 9.81

Ansys Fluent C++

Energy Equation On

Viscous - Realizable k-e Scalable Wall Function

Materials are air, methane and steel

Cell Zone Conditions.

I didn't coupled my interfaces in Mesh Interfaces.

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In my Boundary Condition. There are 2 air mass- flow-inlet, 2 methane mass-flow-inlet, 1 hot mass-flow-inlet. And 5 pressure outlet in total.

All the wall material has been set to Steel.

If you need more details, please leave a comment.

Ansys Fluent Theory Guide

Thank you very much!

Gordon

Ansys Fluent Meshing

Comments

  • edited August 2018

    Hello Gordon,

    Here are some suggestions about your model:

    • Your mesh skewness is really high. Please try to maintain this value below 0.95.
    • Please try to use conformal mesh (rather than non-conformal). This will remove all your mesh interfaces and reduce your model complexity. You will have to perform 'share topology' in SpaceClaim. Here is an excellent video on how to.
    • Please make sure you have sufficient boundary layer mesh corresponding to y+ ~ 40, since you are using scalable wall functions.

    I hope this helps you overcome your convergence issues.

    Thanks.

    Best Regards,

    Karthik

  • Dear all,

    Today, I want to guide you through all the possibilities that could solve this problem, and, in the end, I will give a solution to this problem that will 99% will work with all the cases and solve all the problem related to this issue, especially in the dynamic mesh.

    First of all, you need to make sure these things:

    1-Your mesh is set to CFD, fluent and NOT mechanical

    2- Your mesh should have at least a good skewness and orthogonal array value

    3- you have unstructured mesh, with tringles arrangement

    4-your mesh should show all the bodies of your geometry without cuts

    5-If it did not initialize properly, reset the setting and do it again

    6- for transient application, take PISO as your method

    7- your timesteps must be less than 0.005

    Finally, the real setup that really can solve this problem in the dynamic mesh is to activate

    Implicit Update Settings

    'For transient problems, you can enable implicit mesh updating when you want to have the dynamic mesh updated during a time step (as opposed to just at the beginning of a time step). This capability is beneficial only for applications in which the mesh motion depends on the flow field (for example, cases that use the six DOF solver or involve fluid-structure interaction). For such applications, having the mesh motion updated within the time step based on the converging flow solution results in a stronger coupling between the flow solution and the mesh motion, and leads to a more robust solver run. Implicit mesh updating allows you to run simulations that otherwise could not be solved or would require an unreasonably small time step.' quoted from Ansys help center

    The main reason for this error is usually not the mesh that is not good enough, but the software cannot cope with the changing in the dynamic mesh, so the developers added this technique(Implicit Update Settings) to solve this problem.

    Thank you all ..

    Baqer