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Step 4: Set Up Problem in FLUENT

If you have skipped the previous mesh generation steps 1-3, you can download the mesh by right-clicking on this link. Save the file as nozzle.msh in your working directory. You can then proceed with the flow solution steps below.

Launch FLUENT

Start > Programs > ANSYS 12.0 > Fluid Dynamics > FLUENT> Fluent Inc > FLUENT 6.3.26 > FLUENT 6.3.26

Select 2ddp Select 2D from the list of options and click OK Run.

Import File

Main Menu > File > Read > Case...

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The following should appear in the FLUENT window:

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Check that the displayed information is consistent with our expectations of the nozzle grid. 

Check and Display Grid

First, we check the grid to make sure that there are no errors.

Under Problem Setup > General > Mesh Main Menu > Grid > Check (button)

Any errors in the grid would be reported at this time. Check the output and make sure that there are no errors reported.

Main Menu Grid > Mesh > Info > Size

How many cells and nodes does the grid have?The mesh is being displayed by default but the steps to accomplish this when the grid is not being displayed are the following:

Main Menu > Display > MeshGrid

Make sure all items under Surfaces are is selected. Then click Display. The graphics window opens and the mesh grid is displayed in it.

Some of the operations available in the graphics window are:

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Look at specific parts of the grid by choosing each boundary (centerline, inlet, etc) listed under Surfaces in the Mesh Grid Display menu. Click to select and click again to deselect a specific boundary. Click Display after you have selected your boundaries.

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This should bring up FLUENT 126.0 3 User's Guide in your web browser. If not, access the User's Guide from the Start menu: Start > Programs > ANSYS 12.0 > Help > FLUENT HelpFluent Inc Products > Fluent 6.3 Documentation > Fluent 6.3 Documentation. This will bring up the FLUENT documentation in your browser. Click on the link to the user's guide.

Go to chapter 26 25 in the user's guide. It ; it discusses the Pressure-Based and Density-Based solvers. Section 2625.1 introduces the two solvers:

" In ANSYS FLUENT, two solver technologies are available:Historically speaking, the pressure-based

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approach was developed for low-speed incompressible flows, while the density-based

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approach was mainly used for high-speed compressible flows. However, recently both methods have been extended and reformulated to solve and operate for a wide range of flow conditions beyond their traditional or original intent."

"In both methods the velocity field is obtained from the momentum equations. In the density-based approach, the continuity equation is used to obtain the density field while the pressure field is determined from the equation of state."

"On the other hand, in the pressure-based approach, the pressure field is extracted by solving a pressure or pressure correction equation which is obtained by manipulating continuity and momentum equations."

Mull over this and the rest of this section. So which solver do we use for our nozzle problem? Turn to section 25.7.1 in chapter 25:

"Both solvers can be used for a broad range of flows, but in some cases one formulation may perform better (i.e., yield a solution more quickly or resolve certain flow features better) than the other. The pressure-based and density-based approaches differ in the way that the continuity, momentum, and (where appropriate) energy and species equations are solved, as described in this section in the separate +Theory Guide.+The pressure-based solver traditionally has been used for incompressible and mildly compressible flows. The density-based approach, on the other hand, was originally designed for high-speed compressible flows. Both approaches are now applicable to a broad range of flows (from incompressible to highly compressible), but the origins of the density-based formulation may give it an accuracy (i.e. shock resolution) advantage over the pressure-based solver for high-speed compressible flows."

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