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How can we model forced diffusion in binary mixtures (single phase)?

J = J_ordinary + J_forced

J1_ordinary = -rho D12 Grad yi

J1_forced = -rho^2 * w1 * w2 * y1 * y2 * D12 * (F1 - F2) / (P * W * W)


w1 = mol wt 1
w2 = mol wt 2
y1 = mass fract 1

How can we compute fan pressure drop as a function of radial distance from the center of rotation of the fan (and flow kinetic energy)?

This solution consists of the following files:

* jump.c = UDF to compute dp across fan as a function of (distance from fan center) and flow ke.

* fan_gui.scm = Scheme file for entering fan axis...

How to retrieve the values of specific variables at the nodes of your mesh?

It is sometimes necessary to retrieve the values of specific variables at the nodes of your mesh. This could be done by looping over cells/faces and accessing the interpolated data at the...

What turbulence model should I use to model gas-solid fluidized bed in FLUENT?

For modeling gas-solid fluidized beds, we recommend that you do not use any turbulence model. Please run your cases laminar.

In any gas-solid fluidized bed, including bubbling beds, turbulent...

Can you give me some basic guidance on modeling droplet evaporation in FLUENT 12?

Many users setup a droplet evaporation case in FLUENT and use default settings for material properties for the droplet. This is not correct as those are just placeholders. It is important to note...

I want to evaluate pressure and viscous forces separately in CFD-Post. How do I do this?

The 'force' command in the Function Calculator calculates a combined force (pressure+viscous) on surfaces.

To calculate forces due to pressure and viscous stresses separately, the following form...

How can I set up porous media coefficients given pressure drop versus mass flow rate data?

You can typically get a curve fit of pressure drop versus mass flow rate in the form of equation 1 (

When we compare the values of eq 1 with...

How do I export (e.g Field View) data for post processing during calculation?

Fluent 6.3:

Enter the following TUI command in the execute commands:

Solve ->Execute Commands

Steady Case:


file/export/fud/File_data-%n pressure...

What are the suggested steps if I am having convergence issues for conjugate heat transfer problems?

Suggested solutions if you run into convergence issues:

1) Make sure that the grid at the interface is not too dissimilar.

2) Grid should ideally be very fine at the wall becoming coarser away...

Find out location of a point in the mesh using a UDF

FLUENT solves conservation equations for mass and momentum and stores the solution variables (e.g. temperature, pressure) at the grid cell centroids.

In order to compare the value of the solver...

Check for the Boundary types in UDF

Sometimes it becomes necessary to modify/ operate on a specific type of boundaries dynamically i.e., during the runtime. For this purpose we need to retrieve the type of boundary in an...

Error: divergence detected in AMG solver: pressure correction---what does this mean and how do I fix the problem?

This error message is an indication that the 'pressure correction' equation is diverging. The most likely cause is that the under-relaxation factor (URF) for that equation is too large....

What is the meaning of various terms for pressure like: static, dynamic, total, operating, absolute, gauge, etc. in the context of fluid dynamics?

Static pressure is the pressure at any point in the fluid. This pressure is a function of the state of the fluid, which for an ideal gas, is related to the density/volume of the fluid through the...

How to run repetitive tasks in a FLUENT run, e.g. plot contours of pressure every 5 time steps?

There are multiple ways of doing this. One way is to use execute commands:

Solve->Execute Commands

It opens the execute commands panel and then you can go about the following:

* Set the number...

Are there any general guidelines on selecting a turbulence model?

Some general guidelines on choosing the turbulence modeling options available in Fluent are as follows:

Spalart- Allmaras: Economical for large meshes. Performs poorly for 3D flows, free shear...

What is the difference between the density based and pressure based solver?

The pressure-based approach was historically developed for low-speed incompressible flows, while the density-based approach was mainly used for high-speed compressible flows.

Now both methods...

How can I improve the convergence of calculations involving the use of porous media with a large pressure drop?

In calculations involving the use of porous media, the pressure tends to change rapidly in and around the porous regions of your model. Attempting to resolve these large pressure gradients through...

How do I set up a compressible flow in the segregated solver for a stable solution process?

There are several steps which will work under most circumstances:

In the Material Properties panel, set the density to be "ideal gas".

Initialize the flow domain to near stagnation properties....

Can you give me some recommendations on how I can effectively model transient free surface flows such as in ink jets with FLUENT?

Use the Volume of Fluid (VOF) model in FLUENT to model free surface flows. Some recommendations for the mesh and solver settings are given below:

Although the VOF model will work with any mesh...

how can we assign a pressure inside an internal flow problem?

The inlet velocity boundary condition of an internal flow problem is imposed using a CSV file obtained from a former (upstream) calculation. The use is also interested in having a continuous...

Modeling Swirl Diffuser in Airpak

How to model Swirl Diffuser in Airpak?
In order to model the swirl diffusers, the first thing to make note of is whether the underfloor plenum will be modeled or not.

Lets assume that the...

How to create animations in FLUENT while running the session in batch mode?

In FLUENT one can create animations various ways. A solution-229 explains the number of ways to do that. However, what is the way one can create animations when FLUENT is run in batch mode?


How to write pressure/temperature value along the streamlines?

For a 2D axi-symmetrical problem, is there a way to plot the pressure gradient along the stream line?

I recently ran a simulation for a 2D axi-symmetrical problem. The solution converges. But I...

POLYFLOW - How to identify the several components of a tensor ?

What is a tensor?
What is the meaning of the component Tij of a stress tensor?
What is an invariant of a tensor?
How many components does a tensor have?
What is the meaning of T11, T12, T22 in a...

Non-zero dynamic pressure values on the wall

Dynamic pressure is defined as 0.5*rho*V*V, where rho is the density and V is velocity. At the walls, the no-slip condition forces the velocity to zero, but if I plot the contours of dynamic...