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Q:span-wise drag/lift forces of cylinder

Q:Error: Divergence detected in AMG solver: k

A:Since you were working on convergence issue from past couple of days I would like help you beyond the scope of academic support. Please read the support related guidelines mentioned at the end of email. I am attaching the case and data file which should run without any issue. 1) I have changed the solver setting a bit. Using SIMPLEC algorithm. 2) Hybrid initialization is used.

The time step size set in case file it too large for this kind of unsteady simulation. We need to use small time step size so that the time step should be no larger than the time it takes for a moving cell to advance past a stationary point at interface regions. A dt =1e-4 s should be good in our case.please refer manual1) requirement and limitation of sliding mesh : help/flu_ug/flu_ug_sec_slide_grid_req.html2) Solution stratergies of sliding mesh : help/flu_ug/flu_ug_sec_slide_solve.html

Fluent can handle larger aspect ratio. For some external aerodynamics case even 50000 will work . I think 200 should be alright for this simulation and we can proceed with it.

Please let me know if you have further question.

Q:Time step for turbine using sliding mesh

A: I am looking into your query. The two extra walls are created for non-conformal interfaces and

its alright to go ahead with these extra walls.If your interfaces are completely overlapping each other then these walls will be empty zones.

You will not be able to display them. However in some cases the interfaces need not to be overlapping each other all the time (especially in transient simulations) then the non-overlaping region of interfaces will be modeled as walls.

Please see following section in USER MANUAL

help/flu_ug/x1-2670007.4.1.html (5.4Non-Conformal Mesh Calculations)

Activity Description: Did you convert to unstructured mesh?

Activity Detail:I believe that your .tin and .blk files are correct. However, before writing the Fluent msh file you should right-click on Blocking > Pre-Mesh in the ICEM tree and select 'Convert to Unstruct Mesh'. I think you did not do this but it is essential if you want Fluent to read a multi-block mesh, as in this case. If you then write the output file you should then see in the log:

Running FLUENT V6 Vers. 16.0.0

Creating a Fluent 3D mesh.Computing connectivity for 105435 cells.Creating cell sections for 105435 cells.Checking mesh:

interior faces : 309436 interior walls : 1764 boundary faces : 11974Creating face section for 323174 faces.

Q： Two extra boundary conditions added when export mesh to Fluent

Email from ansys11 June 2015 22:49

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Creating face section for 323174 faces. 1989 faces of part DISC. 307447 faces of part FLUID. 1917 faces of part INLET. 5206 faces of part SYMMETRY. 1917 faces of part OUTLET. 1467 faces of part TOP. 1467 faces of part BED. 405 faces of part DISC_OUT. 405 faces of part DIC_IN. 72 faces of part DISC_WALL.

FLUENT V6 input file written (file: ./fluent.msh) ... done Done Done with translation.

and the attached fluent.msh file will be created. This will then read into Fluent as two separate zones.

Best regards,

there is no need of specifying the BC in ICEM or having two separate fluid regions.

Please do not define BC in ICEM there is no need.

If you create the mesh in one go the porous surface will be treated as conformal and by

default the interior BC will be assigned to it. Then you can change the BC in Fluent to be

porous jump.

In any case I did not receive your attachment so please ensure that you send it so I can

see your problem.

In general, to make two separate mesh solids in ICEM you need to create the enclosing

surfaces and then define a material point in each one belonging to a different part. If the

two solids touch then there should be a surface that separates them. The mesh quality

can be improved by refining the mesh. This can be done, for example, by adding a tetra

size to the surfaces or a mesh density to the volume.

Assuming you are using unstructured meshing, i.e. ICEM Tetra-Prism, I attach a basic

guide to ICEM meshing that you may find useful.

Best regards,

1) Use domain reorder in fluent to speedup and minimize the number roundup errors

( Fluent > > Mesh > Reorder >domain)

2) Turn on Low re, curvature correction and production limiter options under Modes >

viscous > k-omega

I just had quick look at your case.

1) From the image you have shared it seems the case is not converging well. Sometime

divergence could lead to internal solver to stop responding. This seems to be case here.

2) If the case is highly unsteady then its advised to use unsteady solver for better

convergence. The vortex shedding and separation will require a fine resolution mesh in

that locations. The downstream of flow also need to be resolved better.

Some tips

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3) For k-omega models wall yplus on walls ( especially Tower) should be around one.

4) Use "curvature correction" and Low Re option from Models>> viscous >> k-omega .

Please refer the manual for more details of these features.

If you go to DesignModeler, Tools -> Analysis Tools -> Fault Detection

Select rotational geometry You will see blades are having intersections, Thats causing

issue for mesh generation.

Q:check your geometry

Non-conformal meshing

means both the bodies individually meshed and that mesh is independent of each other.

If you put bodies in different parts it will give you nonconformal meshing (please find image

attached with SR).

Q:meshing for 3d turbine

It is doable...

Find one of the 3D wing tutorials and do that first to get your skills up.

Then come back and try this model.

I suggest you subdivide the volume around the blade into 3 sections so you only need to mesh one blade. Setup periodicity and then you can copy/rotate to get the other two thirds.

It may be that the C topology is not the best for a situation where you need periodicity. Perhaps try one of the other basic topologies that I mentioned in that video. Since it is 3D, you should sweep that topology from hub to the boundary of the rotating portion. Add a split for the wing tip[KA1] .

Topology in simple terms is the shape of the block and the relationship between all its

edges. In the context of this tutorial we are simplifying some blocks by collapsing some

edges (this operation merges the nodes along the edge).

Notes:

1. you mesh size in the far-field boundary is too fine, reduce this.

2. If want hexcore mesh, turn off smoothing first and then create a octree mesh (default

method)

3. Smooth the surface to a quality above 0.2

4. create prism mesh

5. create hexacore using Edit mesh > Convert Mesh Type > Tet to Hex > 12 tetra to 1 Hexa

Computational domain: create surface/ standard shapes/ cylinder or box

If you have already slidy the rotating and stationary domains in SolidWorks then try the

following method:

1. Import SolidWorks model via File > Import Model

2. Run build Topology to connect surfaces and make the model water-tight

3. Create Body/Material Point - one in the rotating part and another in the stationary part.

This will allow the mesher to create volumes elements for each domain.

4. Set Max element Global Element Seed[KA2] Size, which is the largest size of the element

you want in the model

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5. Set local mesh sizes for each part i.e. blades, hub, support etc. using Surface Set-up

function[KA3] .

6. Set prism parameters either global or in Part Mesh Setup. Make sure you select the parts

(walls) that you want to inflate the prisms off in Part Mesh Setup

7. Compute mesh and then compute prism mesh.

8. Check Mesh for error and correct, and then check quality. Makes that the over quality of

tetra/prism mesh is around 0.1. You may need to run the smoother a couple of times to

improve the quality.

9. Export to Solver.

The above method can be found in any of the ICEM CFD tutorials in the ANSYS Help

manual.

2)Do i have to build a cylinder around blade to define a rotating domain?

ANS - Thats correct. But reading you question to Sanjay suggests this has already been

done. From SW what you need is a volume that represents the rotating portion of the

model (so a volume slightly bigger than the bladed component, and a volume of the rest of

the model.

4) I follow the tutorials, yet I don't quite understand why. why the body part of geometry is

missing when geometry imported from solidworks to icem?

ANS - ICEM is not a solid modeller and so does not understand the concept of "solids". It is

a surface modelling tool and so deals with enclosed sets of surfaces. In your case you will

achieve two enclosed sets of surfaces - one for the rotating portion and the other for the

rest of the model (with the rotating portion not included). By placing body parts in the two

sets of enclosed surfaces, once the meshing is done it will put the volume mesh into the

Body part present in that enclosed set of surfaces. So in your case at the end of meshing,

you will have two meshes - one that will sit in the Part corresponding to the Body part for

the rotating Volume and one for the Part corresponding to the stationary volume. This will

allow you to select the two mesh independently when you come to apply the physics in the

CFD side.

5) Should I subtract the turbine (solid part) from the fluid domain like the boolean operation

of designmodeler?

ANS - It doesn't really matter. As mentioned in question 4, ICEM doesn't really understand

solids, so whether you subtract one from the other or not will not have any impact in

ICEM. It will still behave the same - so it will still see two enclosed sets of surfaces whether

you subtract one from the other or not.

6) how to build a compational domain (fluid/air domain) in ICEM?

ANS - You do not need to build anything within ICEM as you already have the geometry

created in SW. You will need to run a Build Topology operation and assign the two material

points as Sanjay had in his step by step guide - but you will not need to build a further

"Computational Domain".

A:Is the model Hexa? If so .tin and .blk are sufficient which are rarely too large. If Tetra just .tinis sufficient. Else let me know and I can send a link.

To setup an interface on an ICEM mesh make sure you have two interface mesh parts in the ICEM mesh. I suspect your mesh is connected thus there is only one joining face.

If using Tetra, in Part Mesh Setup choose "split wall" for the interface wall. This will create mesh on both sides. No need for them to be in separate parts as in Fluent they will be separated.

Q:Only one interface zone in Mesh interface

there are two walls at the nacelle (nacelle-inner and nacelle_inner:003) when I list the zones in Fluent(see snapping photo). There should be only one.

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Fluent(see snapping photo). There should be only one.

This happens because the nacelle_inner part has two disconnected faces (see attached). This needs to be fixed in ICEM.

I wanted to do more interation with my .cas and .dat file. The journal is ok, but the out file show "> Halting due to end of file on input". The journal file can't execute the "write data" order.see attached .sh,.jou. and .o files

At line 123 in log file (fluent.o3652065) you will notice that Fluent was asking whether you want to append or replace the monitor data. If you delete old monitor data file then fluent will not ask this question and same journal will work however for appending the monitor data to existing monitors you can modify "it 100' command to "it 100 yes". If you have more than one monitors then you can use "iterate 100 y y .. y " (repeat y for each monitor)

While doing unsteady you can use the command

solve dti 1e-3 20 y y .. y (repeat 15 times)

Here 1e-3 is the time step size (in sec) and 20 is the number of time step sizes.

Q：SR Summary: can't write dat file on cluster

A:There is no equivalent function to the ICEM 'stitch/match edges' function in ANSYS Meshing.

However, if you can choose the same biasing factor for both edges then you can create a single edge sizing for both edges so that the sizing you set will be the same where the two edges join. See the attached 'matching edge spacing' attached.

More generally, you can set your mesh spacings to be parameters within Workbench. Then you can define relationships between these parameters in 'Parameter Set' in the Workbench Project Schematic.

Q:is there a similar function in ansys meshing as the "match edges" function in ICEM CFD?

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Using the number of divisions does not guarantee matching between edges unless the edge lengths are in a simple ratio and you have no biasing. I think it is easier to fix the element size. The element size that you set is multiplied by the biasing factor to determine the element size at the other end of the line. The direction of biasing can also be selected so I think you should be able to match the edges easily.In your case with the wheel, can you set a edge size on the 8 shorter edges that has No Bias with the same Element Size as the long edges. In that way the edge meshes will match at the interface.

Using the number of divisions does not guarantee matching between edges unless the edge lengths are in a simple ratio and you have no biasing. I think it is easier to fix the element size. The element size that you set is multiplied by the biasing factor to determine the element size at the other end of the line. The direction of biasing can also be selected so I think you should be able to match the edges easily.

Concerning the Parameter Set, a description of these capabilities can be found n the ANSYS 16.1 Help Tools > Go to Page: manual help/wb2_help/wb2h_parmdespt.html.

Parameter Set

Time: Fri 18/03/2016 10:59

Statement: I created a mesh for a blade, the sweep method is used for outer computational domain, and the tetra is used for the inner. Thee problem is that the final minimum mesh quality is too low. Can you have a look at my mesh and give me some advice to improving the mesh quality. The archive file is too large to upload.

A: I can see in your model that you are keeping two separate parts, one around the blade and other including rest of the domain with hex mesh. So, I believe you want to keep interfaces in this model. Normally non-conformal interfaces are not recommended in external aero cases, but I understand you are doing this to reduce number of cell counts in order to reduce computation and RAM requirements.

Q:low quality of the mesh for turbine

Coming back to the quality issue you are facing, I can see that the bad elements are around axis.The reason is that you are Sweeping this model about axis, so mesh is revolving about axis. So, the elements nearest to axis are prisms with triangular elements in top and bottom faces of such bodies. As you put more elements on circumference, the corner area of triangle will reduce to a low value of less than 5 degrees and hence the mesh quality issue.

I have recommended an additional slicing in the model. Please refer the attached ppt to this SR.

Meshing-Suggestions

Separate out a small cylindrical region along axis. Now mesh this body Sweeping from Top to Bottom. Sweep all other bodies around axis as earlier. This will give you good mesh as can be seen in ppt file.

A: create an interior _wall and associate block faces to geometric surfacesI just included a new surface (INTERIOR_WALL) and projected the internal faces of the block onto porous and interior_wall.

Q:no mesh in the porous disc, no boundary conditon at the disc

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My model

Model from ansys technician

Technical Details:

Activity Description: Did you convert to unstructured mesh?

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Activity Description: Did you convert to unstructured mesh?

Activity Detail: I believe that your .tin and .blk files are correct. However, before writing the Fluent msh file you should right-click on Blocking > Pre-Mesh in the ICEM tree and select 'Convert to Unstruct Mesh'. I think you did not do this but it is essential if you want Fluent to read a multi-block mesh, as in this case. If you then write the output file you should then see in the log:

Running FLUENT V6 Interface Vers. 16.0.0

Creating a Fluent 3D mesh.Computing connectivity for 105435 cells.Creating cell sections for 105435 cells.Checking mesh:

interior faces : 309436 interior walls : 1764 boundary faces : 11974Creating face section for 323174 faces.

1989 faces of part DISC. 307447 faces of part FLUID. 1917 faces of part INLET. 5206 faces of part SYMMETRY. 1917 faces of part OUTLET. 1467 faces of part TOP. 1467 faces of part BED. 405 faces of part DISC_OUT. 405 faces of part DIC_IN. 72 faces of part DISC_WALL.

FLUENT V6 input file written (file: ./fluent.msh) ... done Done Done with translation.

and the attached fluent.msh file will be created. This will then read into Fluent as two separate zones.

Best regards,

Additional wall and interior1.I try to mesh a blade and hub using ansys meshing. the problem is that here are additional interior and wall in the BC menue of fluent when I export the mesh to Fluent.(the geometry slicing view, fluent BC, and mesh snaps are attached. Sliding mesh module is proposed, geometry is sliced, tetra mesh is used for rotational domain, sweep mesh for stationary cell zones )

1) If you have multiple cell zones attached with a conformal interface then solver will create 'interior' type of BC automatically. You need not do anything for these surfaces and proceed with settings for the other BC.

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with settings for the other BC.2) If you create an interface between two cell zones, then solver will create two additional wall regions which will appear in the BC list. (in my case, three interfaces, thus six walls and interior)

So what you are seeing is expected. I think, you can go ahead with set up of intended BC and run the case.

there are a large descrepancy between numerical result and experimental data. Here I get another question about the pressure reference value. Is the "p" gauge pressure or absolute pressure in in equation 22.3 (P716). It is more easy to understand what i say if you see the attached figure (named pressure

I looked at your question and here is the answer -

1) If you specify operating pressure (it is different from reference pressure) then,p is a gauge pressure. Then please specify gauge value of Pref (= Pref absolute - operating pressure)

2) If operating pressure =0 then,

p is a absolute pressure. Then please specify absolute value of Pref。

Pref should be set as Pref abs - Poperating.So, based on what you have set as operating pressure & what you want to set as absolute reference pressure, you can derive the value of Pref.

Pref = Pref absolute - P operating

I checked your geometry, quality issue is due to sizes that you have defined.as your 1st height is 1.7e-2mm and your face sizing where you are growing prism is near to 11-12mm, it creates huge aspect ratio which leads to deterioration in cell quality.

Here are my suggestion.1. Change inflation settings to last aspect ratio2. Add face sizing of 2mm to faces shown in figure and generate volume mesh it will improve your cell quality. if you further want to increase cell quality. you need to reduce face sizing to 1mm

Please find attached image of sizing applied.

let me know your feedback on this.

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Monitoring Forces and Moments in Unsteady Flow Calculations on cluster

From <https://www.sharcnet.ca/Software/Fluent6/html/ug/node1049.htm > , 28.15.3, 16.1 version,

I runned a unsteady flow simulation on cluster. I know how to save the .dat file, yet do not know how to save the forces and moments on cluster. I tried TUI in window os, it looks like this:/report/forces/wall-forcesyes1 00yes***.frp/report/forces/wall-momentsyes000001yes***.fr

A:There is an option in Fluent GUI to export forces and moments for each time step. Please refer to following sections in the ANSYS Fluent User's Guide:36.16.3. Drag Monitor Dialog Box36.16.5. Moment Monitor Dialog BoxThe drag monitor returns the drag coefficient. However if you need forces you can adjust the reference value to get forces. So in the Reference panel you have to choose reference value for Area, Density and Velocity such that "1/2*Density*Area*Velocity^2" becomes one. For that you can choose Reference value of 2.0, 1.0 and 1.0 for Area, Density and Velocity respectively .

This monitor would write the file in working directory.

I am sorry that I did not understand in the previous update that you are setting the whole case using TUI commands.

There is TUI commands available to set force and moment monitor:

solve/monitors/force/set-drag-monitor

solve/monitors/force/set-moment-monitor

You can also define the reference values using following TUI commands:

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(rp-var-value-set! 'reference-area 2. '#t)

(rp-var-value-set! 'reference-density 1. '#t)

(rp-var-value-set! 'reference-velocity 1. '#t)

I hope this solves your problem. Please let me know if you have any query.

Set the parameters for a new or existing drag coefficient monitor, including the list of wall zoneson which to compute the coefficient, whether to print, plot, and/or write the data, the name ofthe output file (if appropriate), the plot window, and the force vector associated with the coefficientTUI> solve/monitors/force/set-drag-monitormonitor name [cd-1] monitor drag coefficient? [yes] yes()zone id/name(1) [()] 11zone id/name(2) [()] 10zone id/name(3) [()] 16zone id/name(4) [()] print data ? [no] write data? [yes] yesdrag coeff. data file name? ["cd-1-history"] plot data? [no] plot per zone ? [no] x-component of drag vector [0] y-component of drag vector [0] z-component of drag vector [1]

set-drag-monitor

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