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1
Fluent / Re: How can I calculate time-average velocity in transient simulation?
« Last post by boa7128 on December 08, 2016, 10:33:55 AM »
I can not download your attachments, could you please send it to me? jianye_chen@hust.edu.cn. Thx very very much!
You will need to save the data files at regular time intervals, say after every 5 time steps. Now we may at times need to find the "average solution" for the past "n" timesteps from the data files that have already been saved.

The attached User Defined Function (UDF) and Scheme utility will help you to do this.

Example Problem:
The user has iterated the case till timestep no. 200, saving files after every 10 timesteps. Now if the user wants to see the average solution for timesteps 50 to 120 then the attached Scheme utility will load the appropriate data files, call the UDF to find the average of velocity, pressure and turbulence parameters and pass them on to FLUENT. The user will have to save this new averaged data with a new name in order to avoid overwriting the last data.

To use this Scheme utility and UDF, you need to ensure that the data files are saved with appropriate name. A correct naming convention would be "string-x.dat.gz"

std-00020.dat.gz
std-00030.dat.gz
std-00040.dat.gz

Here "std-" is the initial string in the file name, "00x" is the timestep number added as an extension, so that the Scheme utility can recognize the appropriate data file.The usage instructions can be found in the "scm-file.scm" file which you can read using notepad or any text editor.
2
Fluent / Это порно сех
« Last post by SteepenNuh on December 08, 2016, 01:10:19 AM »
Если расстегнуть его змейку на джинсах, можно убедиться, что его желание уже вовсю сконцентрировалось в одном месте и наверняка соображает он уже не головой...
Групповое Сексуальное Издевательство Над Бабой Смотреть
Я пиво людям принес, – парировал Рустик, доставая из-под лежака початую упаковку баночного пива и демонстрируя её в доказательство своих добрососедских намерений.
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Fluent / Setting up a partially-premixed combustion simulation using CHEMKIN database
« Last post by admin on November 13, 2016, 02:57:49 PM »
Procedure for setting up a partially-premixed combustion simulation using materials from CHEMKIN database:

See below:
http://www.clickon.top/FLUENT+V6++Procedure+for+setting+up+a+partiallypremixed+combustion+simulation+using+materials+from+CHEMKIN+database-answer_1184.html

4
Fluent / Partially premixed combustion
« Last post by william on November 13, 2016, 02:55:36 PM »
If I run a partially premixed combustion solution and want to post-process NOx, I have the option to use a Mixture fraction or Temperature NOx PDF. Which is better and why?

The Mixture Fraction PDF is better.

1. It uses the same variance as was solved during the combustion calculation, which is superior to the approximate variance transport equation used for the NOX Temperature PDF

2. Both the number and distribution of the variance points in the NOx PDF, and the variance itself, align exactly with what is used in the combustion calculations, so turbulence interaction treatment is consistent across the calculations.
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CFX / How to restart a run allowing the solver to read the values from a previous file
« Last post by william on November 13, 2016, 02:51:42 PM »
How to restart a run, allowing the solver to read the values from a previous results file, but giving own values for certain variables on domains?

Example1:
The first simulation has been carried out, then simulation1.res is restarted using all variables, except some variables are overwritten with new values.

Example2;
A simulation with two domains D1 and D2. The first simulation has been carried out, then simulation1.res is restarted with the initial values for D1 from simulation1.res and the initial values for D2 are specified manually.

In these situations Initialization with "Automatic" or "Automatic with Value" in CFX Pre will not work, as it will
read the variables from the results file.

In order to achieve this:
1. Create a def file with "Automatic with Value" initialization (for Example2, do not use global initialization
in CFX-Pre, but initialization per domain) and give desired value of variables which you would want solver
to use.
2. In Solver Manager, go to Tools -> Edit CFX-Solver File Edit Definition file and switch the initialization of
the desired variable to be "Value" instead of "Automatic with Value". See Figure 1. This value will be used
for the restart instead results from previous run even if a result file exists.
The same can be done for Example2, letting D1 initialization as "Automatic", and switching D2 initialization
to "Value" entering the desired value.
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Fluent / How to create a Wall Boundary between Solid Zones in FLUENT?
« Last post by william on November 13, 2016, 02:44:47 PM »
Walls between Fluid - Solid zones are created automatically when imported into FLUENT even if not set in the geometry software, but interfaces between two solids are treated as interior zones by default.
The boundary between two solid zones is treated as interior surface by default. In the boundary conditions panel, boundary type can be changed from interior type to wall.
 :D
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Fluent / Tips to set Mass Flow-Rate boundary condition for multiple-face boundary
« Last post by william on November 13, 2016, 02:41:04 PM »
When using a mass-flow-inlet boundary condition, if more than one region is contained within the same
boundary condition zone, the value of the Mass Flow Rate that should be defined is the sum of the individual
mass flow rates, as showed on images attached.
Using this strategy, the resulted inlet velocity will be proportional to face areas.
This can be useful if you have several inlets, once you need to set only one named selection for all inlet
regions and one boundary condition definition.

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Fluent / How to extrude a face zone in Fluent
« Last post by william on November 13, 2016, 02:31:37 PM »
The ability to extrude a boundary face zone allows you to extend the solution domain without having to exit Fluent. A typical application of the extrusion capability is to extend the solution domain when recirculating flow is impinging on a flow outlet. The current extrusion capability creates prismatic or hexahedral layers based on the shape of the face and normal vectors computed by averaging the face normals to the face zones node.
You can define the extrusion process by specifying a list of displacements (in SI units) or by specifying a total distance (in SI units) and parametric coordinates.

mesh/modify-zones/extrude-face-zone-para
mesh/modify-zones/extrude-face-zone-delta

Note: This text command is not available in the parallel version of ANSYS Fluent.
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CFX / Choosing a suitable physical timescale in CFX calculation
« Last post by admin on November 13, 2016, 02:27:21 PM »
For a single phase turbulent flow with or without heat transfer, the 'Auto Timescale' should be used. If you have more complicated physics, such as multiphase flow, flow resistance, or flow with reactions, then you should choose a physical timescale that is appropriate for your physics.

Most physical models require additional source terms and the timescale can often be estimated from them. For example, if we consider a quadratic flow resistance on a filter of length scale, d, then the momentum equation would be:

density*dv/dt = ... + 0.5*Cd*density*(v^2)/d

The timescale, dt, implied by this model is estimated from

v/dt = 0.5*Cd*(v^2)/d or dt = 2*d/(Cd*v)

So if d = 1 mm, Cd = 0.6 and v = about 10 m/s, dt = 3 x 10^-4 s.

The form of the source term can be obtained from the ANSYS CFX theory manual.

Once you have run a first case then look at the last number on the right in the residual table for each iteration in the out file. For example:

----------------------------------------------------------------------
| Equation | Rate | RMS Res | Max Res | Linear Solution |
+----------------------+------+---------+---------+------------------+
| U-Mom-Bulk | 0.84 | 6.3E-05 | 3.4E-03 | 1.6E-03 OK|
| V-Mom-Bulk | 0.87 | 1.4E-04 | 6.5E-03 | 4.4E-03 OK|
| W-Mom-Bulk | 0.84 | 6.3E-05 | 3.8E-03 | 1.5E-03 OK|
| P-Vol | 0.77 | 2.4E-06 | 1.0E-04 | 9.0 2.9E-03 OK|
+----------------------+------+---------+---------+------------------+
| Mass-Fluid1 | 0.91 | 2.3E-05 | 1.2E-03 | 10.7 3.3E-08 OK|

The numbers in the 'Linear Solution' column (1.6E-3, 4.4E-3, etc) tell you the residual from the linear solver but they can also be considered to be the fraction of non-linearity in the equation. Ideally, you want to choose the timescale so that the non-linearity is about 1 or 2% (i.e. 1e-2). If you increase the timescale, the amount of non-linearity also increases in proportion. In the above example, the timescale for u, v, w and p could be increased by a factor of 3 to get faster convergence. However, the mass fraction called 'Mass-Fluid1' has a non-linearity of only 3.3e-8, which is very small. The timescale for this equation (in CFX Pre Solver Control > Equation Class Settings) could be increased by almost 1,000 times, and the calculation would still be stable.
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