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CFX or Fluent for Turbo machinery ?

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Rating: 2 votes, 5.00 average.

CFX or Fluent for Turbo machinery ?

Posted May 27, 2011 at 03:03 by Far

First I would like to say that both flow solvers tend to provide the similar results if the mesh is of good quality and has appropriate no.of nodes and yplus values.

Therfore the first and the most important rule is to make, in any simulation of turbo machinery in particular and external flows in general, high quality mesh with all appropriate parameters e.g. yplus.

Now lets come to the difference

1. CFX has good turbulence models, although after merger with ANSYS all model seems to be incorporated in Fluent as well. Therefore this point does not make any difference any more.

2. Solution time : yes this is big factor where fluent is lagging behind CFX. In my estimate Fluent takes at least 3 days and CFX takes 12-18 hrs for same case (1 million nodes with 4 GB RAM).

3. Scaling : This means with increasing no. of nodes iteration time should not increase. CFX does provide this feature.
For example if you r running a case with 0.5 million mesh size and CFX is taking 12 hrs and fluent is taking 36 hrs. Now you double the mesh size from 0.5 million to 1.0 million. In this case CFX again takes 12 hrs but fluent may take 48 or more hrs. I am assuming you have enough computational resources.

4. Memory management. With CFX you can run 50% higher no of nodes on the same computer. In other words with fluent you can handle 1.0 million and CFX will go up to 1.5 million. Assuming 1.0 million nodes is the limit of your computer for fluent.


I would like to mention again: Fluent and CFX have very little difference in results, the most important thing is the mesh.Therefore instead of solver you should put more emphasis on acquiring the good skill on high end meshing sofwares (GRID PRO is my first choice and then comes ICEM CFD and GRIDGEN)

Best Regards
Far
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Comments

  1. Old Comment
    Far's Avatar
    Regarding the comments 2,3 and 4. These problems in Fluent seems to overcome with the new solver technology such as solution steering, pseudo time control, hybrid initialization and better convergence in version 13.
    Now one can get the same solution in one order less iterations (10000--->> 1000 or even less) with few orders more convergence (instead of 1e-02 to 1e-04).
    Even with the linking to design modeler and ansys meshing (ICEM to be included in workbench in release 14.5) through the ANSYS workbench one can easily perform and update the parametric analysis in Fluent.
    Still I feel that the CFX is better than Fluent in turbo machinery (This can be seen from the latest development in turbo machinery modules in CFX 13.) and Fluent in better in external aerodynamics, two phase modeling, combustion and other (all) type of problems.
    CFX has also better option for two-way FSI.
    Embedded LES is another strong feature of Fluent but What I cannot understand why CFX has still not included the embedded rotating reference module which is available in Fluent V 13.0.
    permalink
    Posted January 15, 2012 at 10:54 by Far Far is offline
    Updated January 15, 2012 at 23:40 by Far
  2. Old Comment
    good Information
    permalink
    Posted February 26, 2012 at 04:45 by Fasri.hatomi Fasri.hatomi is offline
  3. Old Comment
    Far's Avatar

    Even better convergence - Fluent 14

    Convergence is much better with Fluent V 14 as compared to V 12. Results of NACA 0012 tutorial from Fluent are compared for Fluent V 12 and V 14. However there is no change in drag and lift coefficients.


    permalink
    Posted February 26, 2012 at 07:18 by Far Far is offline
  4. Old Comment

    CFX vs Fluent

    Asslamuallikum Sir

    Can transient rotor stator interaction approach in CFX model successfully the turbo machinery cascades with different stator and rotor blade counts i.e. with different pitch ratios (for example if the pitch ration is 0.878) with out any bearing on results? OR if fluent sliding mesh option can account for pitch ratios other than 1?
    Normally in literature i found different methods to account for different pitch ratio's

    1) Phase lag boundary conditions
    2) Harmonic balance methods
    3) Domain Scaling

    I haven't found these methods in Fluent and CFX. May be we have to write UDF's which for the first 2 methods which is an uphill task. And Domain scaling...if someone don't want to use it, what should he do to counter this issue?

    I was doing fan simulation, CFX and fluent pressure based solver didn't work because they were not inducing the flow from rotating to stationary domain due to unknown reasons. When i used the density based solver it worked in the first go and the results were closer to experimental results.

    And Sir, you are right on fluent convergence issues, fluent has some very useful futures as domain reordering, mesh replacing, adaption and repair etc
    permalink
    Posted September 14, 2012 at 14:54 by imran9697 imran9697 is offline
  5. Old Comment
    Anna Tian's Avatar
    Quote:
    Originally Posted by Far View Comment
    Regarding the comments 2,3 and 4. These problems in Fluent seems to overcome with the new solver technology such as solution steering, pseudo time control, hybrid initialization and better convergence in version 13.
    Now one can get the same solution in one order less iterations (10000--->> 1000 or even less) with few orders more convergence (instead of 1e-02 to 1e-04).
    Even with the linking to design modeler and ansys meshing (ICEM to be included in workbench in release 14.5) through the ANSYS workbench one can easily perform and update the parametric analysis in Fluent.
    Still I feel that the CFX is better than Fluent in turbo machinery (This can be seen from the latest development in turbo machinery modules in CFX 13.) and Fluent in better in external aerodynamics, two phase modeling, combustion and other (all) type of problems.
    CFX has also better option for two-way FSI.
    Embedded LES is another strong feature of Fluent but What I cannot understand why CFX has still not included the embedded rotating reference module which is available in Fluent V 13.0.
    Why Fluent is better in external aerodynamics? Any reason behind that?
    permalink
    Posted December 9, 2013 at 06:52 by Anna Tian Anna Tian is offline
  6. Old Comment
    Hello Guys,
    I am working on project Flow field analysis through rotor 37 ANSYS CFX. Could anyone please let me know about which turbulence model is better to get results and why ?
    I really appreciate .
    Thanks
    Manpreet Singh
    manpreet_singh_er@yahoo.co.in
    permalink
    Posted March 17, 2014 at 01:22 by manpreet manpreet is offline
 

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