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allwynpushparaj February 1, 2013 11:38

Beginner help
 
2 Attachment(s)
Hi everyone,
I am a beginner in CFD and am trying to validate the some results of a journal paper and have encountered two problems which later I understood that they are beyond my present knowledge:confused:( i learns fluent, ansys by trial and error method with little theoretical help from my professor). I have stated my problem. Please also view the attachment pics and speak your solutions. Any helpful info will be appreciated.

PROBLEM: I am trying to validate the results at Re= 1, 30,60,200 (I have provided the velocity contours as attached file from the journal that I am trying to validate) and I am facing two problems(I am a biginer so please help).
problem#1 : How does the SCALE function in the Fluent Ansys V12.0 work? It asks for 'Mesh was created in which length unit' and 'View length unit in' with options as mm, cm, m, inch, feet. The gambit mesh file is dimensionless so I am confused with choosing the correct unit and also the contour shape changes with each and every scale I try.
problem#2 : I am getting various vortex lengths for every mesh aspect ratio I try though all the mesh was fine with spacing ratios in the range 0.1 to 0.01 (I also tried coarse mesh as per recommended by the mentioned journal). If one mesh gives a sufficient result for one Re number then the same mesh fails to provide a satisfactory result for another Re number. Is there a criteria defining what mesh ratio must be used for what kinde of problems?
Know the mesh geomentry below. I also tried unstructured meshes.

The velocity contour from the journal that I am trying to validate

Thanks in Advance.

NormalVector February 1, 2013 15:52

Quote:

Originally Posted by allwynpushparaj (Post 405523)
Hi everyone,
I am a beginner in CFD and am trying to validate the some results of a journal paper and have encountered two problems which later I understood that they are beyond my present knowledge:confused:( i learns fluent, ansys by trial and error method with little theoretical help from my professor). I have stated my problem. Please also view the attachment pics and speak your solutions. Any helpful info will be appreciated.

PROBLEM: I am trying to validate the results at Re= 1, 30,60,200 (I have provided the velocity contours as attached file from the journal that I am trying to validate) and I am facing two problems(I am a biginer so please help).
problem#1 : How does the SCALE function in the Fluent Ansys V12.0 work? It asks for 'Mesh was created in which length unit' and 'View length unit in' with options as mm, cm, m, inch, feet. The gambit mesh file is dimensionless so I am confused with choosing the correct unit and also the contour shape changes with each and every scale I try.
problem#2 : I am getting various vortex lengths for every mesh aspect ratio I try though all the mesh was fine with spacing ratios in the range 0.1 to 0.01 (I also tried coarse mesh as per recommended by the mentioned journal). If one mesh gives a sufficient result for one Re number then the same mesh fails to provide a satisfactory result for another Re number. Is there a criteria defining what mesh ratio must be used for what kinde of problems?
Know the mesh geomentry below. I also tried unstructured meshes.

The velocity contour from the journal that I am trying to validate

Thanks in Advance.

  1. The scale function is used to scale your mesh to the right size. Say you created a mesh that was 5in x 5in large. When you read it into Fluent, it will read as 5m x 5m. Specifying your mesh was created in inches changes the dimensions to 0.127m x 0.127m. Of course when you specify something like a mass flow inlet, the speed of the flow will depend on the absolute dimension of your domain (inches, meters).
  2. I'm not sure exactly what to use as a mesh quality indicator in laminar flow besides "adequate resolution", maybe someone else can help? In turbulence modeling, your mesh is usually judged by the y+ value.
If you increase the velocity to change the Reynolds number (and thus a larger wall velocity gradient), it will require a finer mesh near the wall so that may be why you see differences.

vishwas12982 March 13, 2013 12:19

beginner in fluent ...please help..
 
hello.. even i am beginner in FLUENT... can u please tell me the bokks i have to refer to learn fluent. i am also doing project on vortex induced vibrations for a flow overa cylinder.. please help...


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