Tutorial 1: Parallel Plates

Introduction:            In this example you will model fluid flow in the entrance region between two infinite plates. Problem Description:          Air travels between two infinite plates.  For the sake of modeling, these plates will be

assumed to be 1.5 m long and 5 cm apart.         All units are S.I.         Boundary Conditions:            1) Air enters between the plates at a uniform velocity of 0.1 m/s.         Material Properties:            Air:      Density = 1.23 Kg/m3

                        Viscosity = 1.79 e -5         Dimensions            Length = 1.5 m            Width = 0.05 m          Objective: Find the nodal velocity distribution within the air gap between the two plates.         Figure: 

 Basic Outline of the Problem: Preprocessing:1. Start ANSYS.2. Create areas.3. Define the material properties.4. Define fluid element type. (2D Flotran 141 element, which is a 2-D element for fluid analysis.)5. Specify meshing controls / Mesh the areas to create nodes and elements.  Solution:6. Specify boundary conditions. 7. Specify number of iterations for the solution.8. Solve. Postprocessing:9. Plot the contour plot of the velocity distribution.

10. Plot the vector plot of the velocity distribution. Exit:11. Exit the ANSYS program, saving all data.

  Starting ANSYS:          Click on ANSYS 6.1 in the programs menu.         Select Interactive.         The following menu comes up. Enter the working directory. All your files will be stored in

this directory. Also under Use Default Memory Model make sure the values 64 for Total Workspace, and 32 for Database are entered.  To change these values unclick Use Default Memory Model.

 

          Click RUN 

Modeling the Structure: 

          Go to the ANSYS Utility Menu (the top bar). Click Workplane>WP Settings…         The following widow comes up: (notice the numbers are different) 

          Check the Cartesian and Grid Only buttons         Enter the values shown in the figure above. Click OK         Go to the ANSYS Utility Menu (the top bar). Click Workplane>Display Working Plane.

This will display the working grid on the workspace.         Use Utility Menu>PlotCtrls>Pan Zoom Rotate to display the grid as shown in the next

step below.          Next, go to the ANSYS Main Menu (on the left hand side of the screen) and click

Preprocessor>Modeling>Create>Areas>Rectangle>By 2 Corners.         The following window comes up: 

           Click OK once the proper values have been entered.         The model should look like this now: (note, you have a black background) 

  

Element Properties: SELECTING ELEMENT TYPE:          Click Preprocessor>Element Type>Add/Edit/Delete... In the 'Element Types' window

that opens click on Add... The following window opens: 

          Type 1 in the Element type reference number.         Click on Flotran CFD and select 2D Flotran 141. Click OK. Close the 'Element types'

window.         So now we have selected Element type 1 to be a Flotran element. The component will now

be modeled using the principles of fluid dynamics. This finishes the selection of element type.

 DEFINE THE FLUID PROPERTIES:         Go to Preprocessor>Flotran Set Up>Fluid Properties.          On the box, shown below, set the first two input fields as Air-SI, and then click on OK. 

Another box will appear.  Accept the default values by clicking OK. 

          Now we’re ready to define the Material Properties  MATERIAL PROPERTIES 

Go to the ANSYS Main Menu Click Preprocessor>Material Props>Material Models. The following window will appear

 

 As displayed, choose CFD>Density. The following window appears. 

 

 Fill in 1.23 to set the density of Air. Click OK. Now choose CFD>Viscosity. The following window appears: 

 

 Now the Material 1 has the properties defined in the above table so the Material Models window may be closed. 

 

Meshing:          This section is responsible for telling ANSYS how to divide the block such that it has

enough nodes, or points, to produce accurate results.         Go to Preprocessor>Meshing>Size Controls>Manual Size>Lines>All Lines. In the

menu that comes up type 0.01 in the field for Element edge length. 

          Click on OK. Now when you mesh the figure ANSYS will automatically create square

meshes that have an edge length of 0.01m along the lines you selected.          Now go to Preprocessor>Meshing>Mesh Attributes>Default Attributes. The

window is shown below: 

          Make sure that the window matches the one above, click OK, and proceed to

Preprocessor>Meshing>Mesh>Areas>Free         A popup window will appear on the left hand side of the screen.  This window allows you to

select the area to be meshed.  Click within the rectangle you created before and click OK.         The block should now look like this when you are done meshing: 

 

Boundary Conditions and Constraints: 

Go to  Preprocessor>Loads>Define Loads>Apply>Fluid CFD>Velocity>On lines. Pick the left edge block and Click OK. The following window comes up. 

 

 Enter 0.1 in the VX value field and click OK. The 0.1 corresponds to the velocity of 0.1 meters per second of air flowing from the left side. Repeat the above and set the Velocity to ZERO for the air along all of the top and bottom edges.  This is due to the no slip condition.  (VX=VY=0 for all sides) Go to Main Menu>Preprocessor>Loads>Define Loads>Apply>Fluid  CFD>Pressure DOF>On Lines.  Pick the right side of the block and click OK.  This signifies the open end of the pipe. Once all the Boundary Conditions have been applied, the boundary conditions on the plates should look like this: 

 

          Now the Modeling of the problem is done.

 SOLUTION 

Go to ANSYS Main Menu>Solution>Flotran Set Up>Execution Ctrl.          The following window appears.  Change the first input field value to 25, as shown.  No

other changes are needed.  Click OK.  

 Go to Solution>Run FLOTRAN. Wait for ANSYS to solve the problem. Click on OK and close the 'Information' window. 

 POST-PROCESSING 

Plotting the velocity distribution… Go to General Postproc>Read Results>Last Set. Then go to General Postproc>Plot Results>Contour Plot>Nodal Solution. The

following window appears:  

                      Select DOF Solution and Velocity VSUM and Click OK.                     This is what the solution should look like:

 

          Now go to General Postproc>Plot Results>Vector Plot>Predefined. The following

window will appear: 

          Enter the values as shown and click OK. The (zoomed in) plot of velocities will look as

follows.  (Note: this is a zoomed in portion of the entrance of the pipe) 

          A Zoomed in section at the end of the pipe reveals that in fact, a laminar profile has

developed and the velocity yields the correct distribution: 

 

Saving Projects           Simply go to Utility Menu>File>Save As… and save the project using the desired

filename. To open the file later, run Interactive (the first thing explained in this tutorial) as usual, and when that is done, go to Utility Menu>File>Resume From… and choose the saved job from the directory it is saved in.