Fluent and Gambit - Introduction and General Information

Fluent and Gambit - Introduction and General Information

Latest revision: 24 March 2008

Introduction:

"Fluent" is the general name for the collection of computational fluid dynamics(CFD) programs sold by Fluent, Inc. of Lebanon, NH. The Mechanical Engineering Department at Penn State has a site license for Fluent, along with its family of programs. Up to 20 users can run Fluent simultaneously in the Graduate Computing Lab.

Gambit is the program used to generate the grid or mesh for the CFD solver.

Fluent is the CFD solver which can handle both structured grids, i.e. rectangular grids with clearly defined node indices, and unstructured grids. Unstructured grids are generally of triangular nature, but can also be rectangular. In 3-D problems, unstructured grids can consist of tetrahedrals (pyramid shape), rectangular boxes, prisms, etc.
Note: Since version 5.0, Fluent can solve both incompressible and compressible flows.
The normal procedure in any CFD problem is to first generate the grid (with Gambit), and then to run Fluent.

Instructions:

In these learning modules, different types of formatting are used to save writing, as follows:

Italic text is used to indicate the name of a window or the name of a parameter within a window. For example, if a window has the title "Meshing an Edge", and within that window is a parameter called "Number of nodes", an instruction will appear as follows: In Meshing an Edge, change Number of nodes to 16.

Underlined text implies that the user should click on the corresponding button or option with the left mouse button.
R-Underlined text preceded by an R means to use the right mouse button rather than the standard left mouse button.
When two or more underlined texts are shown with a dash, like this: First-Second, the user should click with the left mouse button on the first item, which will open up a new pop-up window or selection box. In the new window, the user clicks on the second item (Sometimes the mouse button must be held down without releasing in order to open up this new window. In that case, the user releases the mouse button when it is positioned over the desired selection in the second window.)
Sometimes, left clicks and right clicks are required for a specific task. The R will indicate a right click in these cases, since left click is the default. For example, Edge Command Button-R-Create Edge-NURBS.
When text is to be entered with the keyboard, it will be shown in double quotes. For example, Type "text" means to type the text within the quotes, but not the quotes themselves.
When the Enter key is to be pressed after typing, this will be indicated in these learning modules as Enter "text" instead of Type "text". For example, Enter "fluent 2d &" means to type the words in double quotes, and then hit the Enter key on the keyboard.

Selecting in Gambit:

Most commands in Gambit require the user to select an object (a vertex, en edge, etc.). To select an object, hold down the Shift key on the keyboard, and click on the object with the left mouse button. In most cases, an alternate way to select is provided by a List window, which allows the user to click on object(s) from the Available column, and transfer them to the Picked column. This is especially useful when an operation is to be done on many objects at the same time.
In cases where more than one object can be selected by the same click (for example two faces which share an edge), the first Shift click may pick the "wrong" one. In such a case, Shift click with the middle mouse button until the desired one is selected.

Graphical Manipulation:

Graphical manipulation means zooming in and out, moving objects around, rotating objects, etc. Unfortunately, the mouse commands for Gambit and Fluent are different for these manipulations. Note, a 3-button mouse is assumed. If you have a two-button mouse, the normal default is that clicking both left and right buttons simultaneously denotes a middle mouse click.

In Gambit, the left mouse button controls rotation, the middle controls location, and the right controls zoom. Click and move the left mouse button to rotate. This takes some practice. Click and drag the middle mouse button to move the image. Click and drag down the right mouse button to zoom in, and click and drag up the right mouse button to zoom out.
In Fluent, the mouse functions depend on whether the flow is 2-D or 3-D. If 2-D, click and drag the left mouse button to move the image around. The graphical display can be zoomed-in or zoomed-out with the middle mouse button. If you start on the upper left and draw a rectangle with the middle mouse button towards the lower right, the display will zoom in on what is included in the rectangle. If you draw a rectangle backwards with the middle mouse button, i.e. from the lower right to the upper left, it will zoom out. The right mouse button simply identifies the boundary or type of cell on which you click. In 3-D flow, the left mouse button controls rotation if it is dragged. If the left button is just clicked somewhere, that point is moved to the center of the display. Other functions in 3-D are essentially the same as in 2-D.

Running Fluent in Background Mode:

When many iterations are required, it is possible (and preferrable) to run fluent in background mode. This enables a user to logout of the computer while fluent churns away in the background. This is especially useful when the solution requires several hours of CPU time - in cases like that, it is best to run at night. For detailed instructions on how to run Fluent in background mode, see the learning module, fluent_background.htm .