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Distinguished Contributor
jrm_1971
Posts: 112
Registered: ‎03-31-2011

Grey "i", mesh dian, vel rep problems, transient results

242 Views, 16 Replies
11-05-2012 07:27 AM

1. What do the grey "i" icons next to the following mean after meshing? What are the diagnostic arrows telling me?

 

Surface Refinement: False

Gap Refinement: False

Length Scale: 1.4

 

When I hover over Length Scale, it is giving the option for Diagnostics. When I do diagnostics it is showing arrows for potential problems found, the arrows are not normal to the surface. The arrows are shown at the inlet/outlet.

 

My analysis is a 0.406" ID closed conduit with volumetric flow rate and temperature BCs at the inlet and pressure at the outlet.

 

I have refined the mesh for the conduit and fluid (gas).

 

2. Also, when I do velocity traces (center away from the wall) on the surface normal to the inlet, the traces only go so far (long spiral conduit 35 ft lg.). Does this mean the fluid is not going all the way through the conduit? Good engineering sense tells me gas should fill a small diameter conduit quickly. Is there a way to probe individual points on the inlet/outlet for velocity? Is k-epsilon the best turbulent setting for small diameter closed conduit?

 

I have done 100 iterations both steady state and transient, compressible and incompressible. It is turbulent flow with Mach number below 0.5.

 

3. For transient results, shouldn't I be able to move through the VCR buttons forward and backward to see each iteration? It stays stuck at 100 (Last). I would like to see the results (velocity, temperature, heat flux) in correlation with time.

 

 

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wildej
Posts: 972
Registered: ‎08-25-2011

Re: Grey "i", mesh dian, vel rep problems, transient results

11-05-2012 08:37 AM in reply to: jrm_1971

1a) As far as I know the 'i' is just for information.

b) The diagnostic arrows are different, I assume you were within the Edge thumbnail of the mesh diagnostics? Check the help as it describes it well, but they are showing you the edges that are the same or shorter than the size you have specified. We often increase this value to reduce the mesh count or avoid issues with tiny edges.

 

2) Has the model converged? Is the mesh sufficient to capture the flow?

ADV4 is helpful for flows in very thin pipe work 

Be very careful with the setup of sub-sonic/compressible analyses, you cannot use the standard BC's, check out the help again but post if you need more information.

Use a cut-plane to probe individual points, hold down the shift key and float the cursor over the plane.

 

3) No, only if you save out results at specified intervals (Solve -> Save intervals). These can quickly fill a hard drive or cause an analysis to become huge so we recommend saving 20-30 or so over the entire duration of an analysis.



Jon Wilde
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Distinguished Contributor
jrm_1971
Posts: 112
Registered: ‎03-31-2011

Re: Grey "i", mesh dian, vel rep problems, transient results

11-05-2012 03:19 PM in reply to: wildej

1a) As far as I know the 'i' is just for information.

b) The diagnostic arrows are different, I assume you were within the Edge thumbnail of the mesh diagnostics?(I have no idea what Edge thumbnail is. I right clicked the "i" next to the category allowing for diagnostics and clicked the diagnostics button in that dialog box) Check the help as it describes it well, but they are showing you the edges that are the same or shorter than the size you have specified. We often increase this value to reduce the mesh count or avoid issues with tiny edges. (Please provide a link. I feel like being dropped in the forrest without a compass).

 

2) Has the model converged? Is the mesh sufficient to capture the flow? (The analysis converged and the mesh is 1/2 the default)

ADV4 is helpful for flows in very thin pipe work

Be very careful with the setup of sub-sonic/compressible analyses, you cannot use the standard BC's, check out the help again but post if you need more information. (Link please, forrest issue again).

Use a cut-plane to probe individual points, hold down the shift key and float the cursor over the plane.

 

3) No, only if you save out results at specified intervals (Solve -> Save intervals). These can quickly fill a hard drive or cause an analysis to become huge so we recommend saving 20-30 or so over the entire duration of an analysis.

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Product Support
wildej
Posts: 972
Registered: ‎08-25-2011

Re: Grey "i", mesh dian, vel rep problems, transient results

11-06-2012 02:25 AM in reply to: jrm_1971

b) The diagnostic arrows are different, I assume you were within the Edge thumbnail of the mesh diagnostics?(I have no idea what Edge thumbnail is. I right clicked the "i" next to the category allowing for diagnostics and clicked the diagnostics button in that dialog box) Check the help as it describes it well, but they are showing you the edges that are the same or shorter than the size you have specified. We often increase this value to reduce the mesh count or avoid issues with tiny edges. (Please provide a link. I feel like being dropped in the forrest without a compass).

 

Are you aware than you can press the small blue '?' icon at any point to be taken to the help?

Or search the help for 'edge diagnostics' and you should find this, the help is a great place to start.

 

The edge and surface diagnostics can be accessed from the meshing window 'diagnostics'. Sounds like you have found this already, there are 2 thumbnails here. Edge and Surface. The help describes what these do better than I did above.

 

2) Has the model converged? Is the mesh sufficient to capture the flow? (The analysis converged and the mesh is 1/2 the default) Are you able to share the support file (cfz)?

ADV4 is helpful for flows in very thin pipe work

Be very careful with the setup of sub-sonic/compressible analyses, you cannot use the standard BC's, check out the help again but post if you need more information. (Link please, forrest issue again).

 

From the help 'internal compressible flow'. It is best here to work on one model at a time, can I ask if you have had training or access to formal training through a reseller/partner?



Jon Wilde
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Distinguished Contributor
jrm_1971
Posts: 112
Registered: ‎03-31-2011

Re: Grey "i", mesh dian, vel rep problems, transient results

11-06-2012 10:20 PM in reply to: jrm_1971

I think I see where the misunderstanding is. You good friends on the other side of the pond are calling what we call "tab" "thumb nail" got it. After reviewing the help and tooling around in the program, I am not seeing how to refine the problematic edges and sufaces.

 

Also, what is ADV4? That is not in the "help".

 

From the description from the help for internal compressible flow, I don't believe the hand calculated Mach number of about 0.5 is close enough to the 0.8 recommended in the help. I would appreciate elaborating what is meant by "Be very careful with the setup of sub-sonic/compressible analyses, you cannot use the standard BC's". However, tweeking the problematic edges and surfaces may result in mesh that allows for proper analysis. Please advise.

 

No formal training at this time due to $$$. It's you and me.

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Distinguished Contributor
jrm_1971
Posts: 112
Registered: ‎03-31-2011

Re: Grey "i", mesh dian, vel rep problems, transient results

11-06-2012 10:26 PM in reply to: jrm_1971

Also, when I hit "Solve" for the transient case, it did not give me the option to save intervals

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Product Support
wildej
Posts: 972
Registered: ‎08-25-2011

Before you hit 'solve' but within the first thumbnail (co...

11-08-2012 12:10 AM in reply to: jrm_1971

Before you hit 'solve' but within the first thumbnail (control) of the solve window you should see the option to 'save intervals' as below. This analysis is set to save out results every 50 timesteps (in this case it would be every 50 seconds)

 

Save Intervals.jpg



Jon Wilde
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Distinguished Contributor
jrm_1971
Posts: 112
Registered: ‎03-31-2011

Re: Before you hit 'solve' but within the first thumbnail (co...

11-09-2012 09:47 PM in reply to: wildej

1. After reviewing the help and tooling around in the program, I am not seeing how to refine the problematic edges and sufaces.

 

2. Also, what is ADV4? That is not in the "help".

 

3. From the description from the help for internal compressible flow, I don't believe the hand calculated Mach number of about 0.5 is close enough to the 0.8 recommended in the help. I would appreciate elaborating what is meant by "Be very careful with the setup of sub-sonic/compressible analyses, you cannot use the standard BC's". However, tweeking the problematic edges and surfaces may result in mesh that allows for proper analysis. Please advise.

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Distinguished Contributor
jrm_1971
Posts: 112
Registered: ‎03-31-2011

Re: Before you hit 'solve' but within the first thumbnail (co...

11-11-2012 11:45 AM in reply to: wildej

OK somehow being able to save the results wasn't available before but now it is.

 

1. After reviewing the help and tooling around in the program, I am not seeing how to refine the problematic edges and sufaces.

 

2. Also, what is ADV4? That is not in the "help".

 

3. From the description from the help for internal compressible flow, I don't believe the hand calculated Mach number of about 0.5 is close enough to the 0.8 recommended in the help. I would appreciate elaborating what is meant by "Be very careful with the setup of sub-sonic/compressible analyses, you cannot use the standard BC's". However, tweeking the problematic edges and surfaces may result in mesh that allows for proper analysis. Please advise.

 

NEW NEW NEW

 

4. Now I am getting the warning below. I am most interested in how to do "3". I am not able to find that option.

warning.jpg

 

5. Please see the image below. The diagnostics is occuring before and  after meshing. The conduit/fluid is split (at the 1/2 line) becuase the geometry upstream will not allow for cutting planes to view the behavior. Is there a way to refine the problematic edges/surfaces? Refining the mesh doesn't fix it.

cfd post.jpg

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Product Support
wildej
Posts: 972
Registered: ‎08-25-2011

Re: Before you hit 'solve' but within the first thumbnail (co...

11-12-2012 12:32 AM in reply to: jrm_1971

Good morning,

 

1) t looks as though the geometry here may have some issues, they might be where that split line is but I cannot tell. Where is surface 37?

Find it first. Then when in meshing, switch to 'Surface Selection', Select it, Refine it, then press Apply and Spread Changes. You may also need to fix it in CAD, it depends if the issue is bad geometry or simply not enough mesh to capture it properly.

 

2) ADV4 is Advection Scheme 4. Search for Advectino Scheme, this will come up in the help, sorry for the confusion.

 

3) Start with an incompressible model. What is your maximum velocity?

 

4) The Small Object and Edge Merge Tools are underneath the 'Geometry' tab. If they were necessary, the Geometry dialogue box would likely have popped up when you launched into CFD in the first place. If it ever does, run throuh the first 2 thumbnails, merging edges and then removing small ojbects if necessary. These are only meshing tequniques though, we aren't actually fixing bad CAD.

 

5) Your comment here is not too clear to me. The positioning of the cutting planes within CFD is not at all related to geometry, so you can position them wherever you like, no need for split lines. It looks to me like you need to fix an issue that you have in CAD, keep things simple.



Jon Wilde
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