Tutorial -1 Fluid Flow and Heat Transfer in a Mixing Elbow

Problem Description

A cold fluid at 293.15 K flows into the pipe through a large inlet and mixes with a warmer fluid at 313.15 K that enters through a smaller inlet located at the elbow. The mixing elbow configuration is encountered in piping systems in power plants and process industries. It is often important to predict the flow field and temperature field in the area of the mixing region in order to properly design the junction.

Meshing the Geometry in the ANSYS Meshing Application

Now that we have created the mixing elbow geometry, we must generate a computational mesh throughout the flow volume. For this section , we will use the ANSYS Meshing application to create a mesh for your CFD analysis, then review the list of files generated by ANSYS Workbench.

  1. Open the ANSYS Meshing application.

In the ANSYS Workbench Project Schematic, double-click the Mesh cell in the elbow fluid flow analysis system (cell A3). This displays the ANSYS Meshing application with the elbow geometry . we can also right-click the Mesh cell to display the context menu where we can select the Edit… option.

Geometry successfully created in fluent -design modeler

                  The ANSYS Meshing Application with the Elbow Geometry Loaded

2. Create named selections for the geometry boundaries.

In order to simplify  work on in ANSYS Fluent, label each boundary in the geometry by creating named selections for the pipe inlets, the outlet, and the symmetry surface.

a. Select the large inlet in the geometry that is  in the ANSYS Meshing application.

b. Right-click and select the Create Named Selection option.

Named selection window

c. In the Selection Name dialog box, enter velocity-inlet-large for the name and click OK.

d. Perform the same operations for:

  • The small inlet (velocity-inlet-small)
  • The large outlet (pressure-outlet)
  • The symmetry plane (symmetry).

3. Create a named selection for the fluid body.

  1. Change the selection filter to Body in the Graphics Toolbar
  2. Click the elbow in the graphics display to select it.
  3. Right-click, select the Create Named Selection option and name the body Fluid.

4.Set basic meshing parameters for the ANSYS Meshing application.

         a. In the Outline view, select Mesh under Project/Model to display the Details of “Mesh”           view below the Outline view.

b. Sizing node can be expand  by clicking the “+” sign to the left of the word Sizing to reveal additional sizing parameters. Change Relevance Center to Fine by clicking the default value, Coarse, and selecting
Fine from the drop-down list.

c. Expand the Quality node to reveal additional quality parameters. Change Smoothing to High.

d. Add a Body Sizing control.

e. Click again Mesh in the Outline view and in the Details of “Mesh” view, expand the Inflation node to reveal additional inflation parameters. Change Use Automatic Inflation to Program Controlled.

5. Generate the mesh.
Right-click Mesh in the project Outline tree, and select Update in the context menu.

Meshing

6. Close the ANSYS Meshing application.

 ANSYS Meshing applicationcan beclosed without saving  because ANSYS Workbench automat- ically saves the mesh and updates the Project Schematic accordingly. The Refresh Required icon in the Mesh cell has been replaced by a check mark, indicating that there is a mesh now associated with the fluid flow analysis system.

7. View the list of files generated by ANSYS Workbench.

Setting Up the CFD Simulation in ANSYS Fluent

1.In the ANSYS Workbench Project Schematic, double-click the Setup cell in the elbow fluid flow analysis

system.we can also right-click the Setup cell to display the context menu where we can select the Edit option

Fluent window

2. Ensure that the proper options are enabled.

a. Ensure that Serial from the Processing Options list is enabled.

b. Select Double Precision under Options.

c. Ensure that the Display Mesh After Reading and Workbench Color Scheme options are enabled.

3. Click OK to launch ANSYS Fluent.

Setting Up Domain

In this step,  mesh-related activities will be performed using the Setting Up Domain ribbon tab (Mesh group).

1. Change the units for length.

This displays the Set Units dialog box.

Set units
  1. Select length in the Quantities list.
  • Select mm in the Units list.
  • Close the dialog box.
  • Check the mesh.
  • Review the mesh quality.

Setting Up Physics

In the steps ,  a solver is selected and specify physical models, material properties, and

zone conditions for your simulation using the Setting Up Physics ribbon tab.

1. In the Solver group of the Setting Up Physics ribbon tab, retain the default selection of the steady pressure based

solver.

Setting Up Physics Solver

2. Models are set up for the CFD simulation using the Models group of the Setting Up Physics ribbon tab.

  1. Enable heat transfer by activating the energy equation.
  2. Enable the – turbulence model.
select viscous model as k-epsilon

3.Set up the materials for your CFD simulation using the Materials group of the Setting Up Physics ribbon tab.

a. In the Setting Up Physics ribbon tab, click Create/Edit… (Materials group).

Setting Up Physics Materials Create/Edit…

b. In the Create/Edit Materials dialog box, type water for Name.

c. Click Change/Create.

d. Ensure that there are now two materials (water and air) defined locally by examining the Fluent Fluid Materials drop-down list in the Create/Edit Materials dialog box .

e. Close the Create/Edit Materials dialog box.

4. Set up the cell zone conditions for the CFD simulation using the Zones group of the Setting Up Physics ribbon tab.

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select cell zones
  1. In the Setting Up Physics tab, click Cell Zones.

Setting Up Physics Zones Cell Zones

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b. Set the cell zone conditions for the fluid zone.

5. Set up the boundary conditions for the CFD analysis using the Zones group of the Setting Up Physics ribbon tab.

  1. In the Setting Up Physics tab, click Boundaries (Zones group).

Setting Up Physics Zones Boundaries

b. Set the boundary conditions at the cold inlet (velocity-inlet-large).

c. In a similar manner, set the boundary conditions at the hot inlet (velocity-inlet-small),

d. Double-click pressure-outlet and set the boundary conditions at the outlet, as shown in the given below Pressure Outlet dialog box.

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Solving

In the steps ,  set up and run the calculation using the Solving ribbon tab are being done.

1.Set up solution parameters for the CFD simulation.

a. The Gradient method is changed.

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b. plotting of residuals during the calculation is enabled.

c. Create a surface report definition at the outlet (pressure-outlet).
Solving Reports Definitions New Surface Report Facet Maximum

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d. In the tree, double-click the temp-outlet-0-rfile and ex- amine the report file settings in the Edit Report File dialog box.

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e. In the tree, double-click temp-outlet-0-rplot (under Solution/Monitors/Report Plots) and examine the report plot settings in the Edit Report Plot dialog box.

f. Initialize the flow field using the Initialization group of the Solving ribbon tab.

Solving Initialization

g. Check to see if the case conforms to best practices.

Solving Run Calculation Check Case

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2. Calculate a solution using the Run Calculation group of the Solving tab.

Solving Run Calculation

a. Start the calculation by requesting 300 iterations.

  1. Enter 300 for No. of Iterations.
  2. Click Calculate.

b. Examine the plots for convergence

With ANSYS Fluent still running, go back to ANSYS Workbench and view the list of generated files.

View Files

Displaying Results in ANSYS Fluent and CFD-Post

In this step,  display the results in CFD- Post, and then review the list of files generated by ANSYS Workbench.

1. Display results in ANSYS Fluent using the Postprocessing ribbon tab.

In ANSYS Fluent,  a simple evaluation of the velocity and temperature contours on the symmetry plane can be performed.  CFD-Post (from within ANSYS Workbench) to perform the same evaluation will be used later.

a. Display filled contours of velocity magnitude on the symmetry plane (Figure 1.17: Velocity Distribution Along Symmetry Plane (p. 53)).

Postprocessing Graphics Contours Edit…

In the Contours dialog box, in the Options group, enable Filled.
Ensure that Node Values is enabled in the Options group. FromtheContoursofdrop-downlists,selectVelocity…andVelocityMagnitude.

From the Surfaces selection list, deselect all item by clicking and then select symmetry. Click Display to display the contours in the active graphics window.

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                     Velocity Distribution Along Symmetry Plane

b. Display filled contours of temperature on the symmetry plane  

Postprocessing Graphics Contours Edit…

c. The ANSYS Fluent application is closed.

File Close Fluent

d. View the list of files generated by ANSYS Workbench.

View Files

2.Display results in CFD-Post.

a. Start CFD-Post.

In the ANSYS Workbench Project Schematic, double-click the Results cell in the elbow fluid flow analysis system (cell A6). This displays the CFD-Post application. You can also right-click the Results cell to display the context menu where you can select the Edit… option.

b. Reorient the display.

c. Ensure that Highlighting is disabled.

d. Display contours of velocity magnitude on the symmetry plane

e. Display contours of temperature on the symmetry plane

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3. Close the CFD-Post application by selecting File Close CFD-Post or by clicking the ‘X’ in the top right corner of the window.

4. The elbow-workbench project in ANSYS Workbench is saved.

5 The list of files generated by ANSYS Workbench is viewed.

View Files

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