Chapter 3: Simulating Flow in a Static Mixer Using Workbench

This tutorial simulates a static mixer consisting of two inlet pipes delivering water into a mixing vessel; the water exits through an outlet pipe. A general workflow is established for analyzing the flow of fluid into and out of a mixer using ANSYS Workbench.

This tutorial includes:

Tutorial Features Overview of the Problem to Solve Before You Begin Starting ANSYS Workbench Starting CFX-Pre from ANSYS Workbench Obtaining a Solution Using CFX-Solver Manager Viewing the Results in CFD-Post

3.1. Tutorial Features

In this tutorial you will learn about:

Using ANSYS Workbench to set up a project. Using Quick Setup mode in CFX-Pre to set up a problem. Using ANSYS CFX-Solver Manager to obtain a solution. Modifying the outline plot in CFD-Post. Using streamlines in CFD-Post to trace the flow field from a point. Viewing temperature using colored planes and contours in CFD-Post. Creating an animation and saving it as a movie file.

Component Feature Details

CFX-Pre User Mode Quick Setup Wizard

Analysis Type Steady State

Fluid Type General Fluid

Domain Type Single Domain

Turbulence Model k-Epsilon

Heat Transfer Thermal Energy

Boundary Conditions Inlet (Subsonic)

Outlet (Subsonic)

Wall: No-Slip

Wall: Adiabatic

Timestep Physical Time Scale

CFD-Post Animation Keyframe

Component Feature Details

Plots Contour

Outline Plot (Wireframe)

Point

Slice Plane

Streamline

3.2. Overview of the Problem to Solve

This tutorial simulates a static mixer consisting of two inlet pipes delivering water into a mixing vessel; the water exits through an outlet pipe. A general workflow is established for analyzing the flow of fluid into and out of a mixer.

Water enters through both pipes at the same rate but at different temperatures. The first entry is at a rate of 2 m/s and a temperature of 315 K and the second entry is at a rate of 2 m/s at a temperature of 285 K. The radius of the mixer is 2 m.

Your goal in this tutorial is to understand how to use CFX in Workbench to determine the speed and temperature of the water when it exits the static mixer.

Figure 3.1  Static Mixer with 2 Inlet Pipes and 1 Outlet Pipe

3.3. Before You Begin

It is important to do the following before beginning the tutorial:

1. Use your operating system's tools to create a directory for your project's files. The directory you create will be referred to as the working directory.

2. Copy StaticMixerMesh.gtm from the <CFXROOT>/examples directory to the working directory, where <CFXROOT> is the installation directory for ANSYS CFX.

3.4. Starting ANSYS Workbench

1. Start ANSYS Workbench.

To launch ANSYS Workbench on Windows, click the Start menu, then select All Programs > ANSYS 13.0 > Workbench. To launch ANSYS Workbench on Linux, open a command line interface, type the path to “runwb2” (for example, “~/ansys_inc/v130/Framework/bin/Linux64/runwb2”), then press Enter.

2. In the Toolbox pane, open Component Systems and double-click CFX.

A CFX system opens in the Project Schematic.

Note: You use a CFX component system because you are starting with a mesh. If you wanted to create the geometry and mesh, you would start with a Fluid Flow (CFX) analysis system.

3. From the tool bar, click Save As  . In the dialog that appears, browse to the working directory, give the File name as StaticMixer, and click Save.

4. Right-click on the blue CFX cell (A1) and select Rename. Change the name of the system to Static Mixer.

.5. Starting CFX-Pre from ANSYS Workbench

Because you are starting with an existing mesh, you can immediately use CFX-Pre to define the simulation. To launch CFX-Pre:

1. In ANSYS Workbench, enable View > Files and View > Progress so that you can see the files that are written and the time remaining to complete operations.

2. In the Workbench Project Schematic, double-click the Setup cell of the CFX component system. CFX-Pre opens.

3. Optionally, change the background color of the viewer in CFX-Pre for improved viewing:

a. Select Edit > Options. The Options dialog box appears.b. Adjust the color settings under CFX-Pre > Graphics Style. For example, you

could set the Background > Color Type to Solid and the Color to white.c. Click OK.

3.6. Obtaining a Solution Using CFX-Solver Manager

To obtain a solution, you need to launch the CFX-Solver Manager and subsequently use it to start the solver:

1. Double-click on the ANSYS Workbench Solution cell. The CFX-Solver Manager appears with the Define Run dialog box displayed.

The Define Run dialog box enables configuration of a run for processing by CFX-Solver. In this case, all of the information required to perform a new serial run (on a single processor) is entered automatically. You do not need to alter the information in the Define Run dialog box.

2. Click Start Run.

CFX-Solver launches and a split screen appears and displays the results of the run graphically and as text. The panes continue to build as CFX-Solver Manager operates.

One window shows the convergence history plots and the other displays text output from CFX-Solver. The text lists physical properties, boundary conditions, and various other

parameters used or calculated in creating the model. All the text is written to the output file automatically (in this case, StaticMixer_001.out).

Note: Once the second iteration appears, data begins to plot. Plotting may take a long time depending on the amount of data to process. Let the process run.

3.7. Viewing the Results in CFD-Post

When CFD-Post starts, the viewer and Outline workspace are displayed. Optionally, change the background color of the viewer improved viewing:

1. In CFD-Post, select Edit > Options. The Options dialog box appears.2. Adjust the color settings under CFD-Post > Viewer. For example, you could set the

Background > Color Type to Solid and the Color to white.3. Click OK.

The viewer displays an outline of the geometry and other graphic objects. You can use the mouse or the toolbar icons to manipulate the view, exactly as in CFX-Pre