Tutorial 3 Diverging Flow

7/30/2019 Tutorial 3 Diverging Flow

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Tutorial 3: Diverging Flow

Introduction: In this example laminar fluid flows over an angled flate platePhysical Problem: Compute and plot the velocity distribution of a flowProblem Description:

Objective:o To plot the velocity profile

o The duct has an entrance region of and an exit region of . These two regions are seperated by a

horizontal distance of .o The at infinite distance from the plate is . This velocity best demonstrates the

recirculation zone while keeping the flow inside the duct laminar.

:

Basic Outline of the Problem: Preprocessing:1. Start ANSYS.


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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 solution iterations.8. Solve. Postprocessing:9. Plot the contour plot of the velocity distribution.10. Plot the velocity plot of the velocity distribution. Exit:11. Exit the ANSYS program, saving all data. STARTING ANSYS

Click on ANSYS 5.6 in the programs menu. Select .

The following menu that comes up. Enter the working directory. All your files will be stored in this directory. Also enter 64 forTotal Workspace and 32 for Database. Click on Run.


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Go to the ANSYS Main Menu To create the entrance region click . The

and the . Starting position is at (0,0).

To create the exit region click . The

and the . Starting position is at (2,0).


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To create the connecting region, click .Select the four keypoints that make up the region and click OK. The area will be created automatically:


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Modeling is now done:


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ELEMENT PROPERTIES SELECTING ELEMENT TYPE:

Click ... In the 'Element Types' window that opens click on Add... The followingwindow opens.


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Type in the . Click on and select . Click . Close the window. So now we have selected Element type to be solved using , the computational fluid dynamics portion of ANSYS. This

finishes the selection of element type. MESHING

To clarify meshing you should plot by lines. To do this click on the file menu. Go to . Select the four vertical lines and click OK


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In the window that comes up type in the 'Element edge length' box and in the Spacing Ratio box. This puts moreelements near the walls than in the middle:


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Now Click . Now go to and select the top and bottom lines of the

entrance and exit region:


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Enter 15 for the number of element divisions, and enter 1 for the Spacing Ratio. Now go to and select the top and bottom of the

transition region. Enter 20 for the number of element divisions, and 1 for the Spacing Ratio. Click OK. Now go to . Click the three area's or click 'Pick All' and then . Meshing is done. Your mesh should look like this:


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Go to On the box, shown below, set . Then click on .


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BOUNDARY CONDITIONS AND CONSTRAINTS

To make loading easier, go to on the main file menu. Go to . Pick the left line of the entrance region

and Click :

Enter and . Leave VZ blank. Then click . This number corresponds to the velocity of 0.003

meter per second of air flowing from the left side:


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The walls of the duct are stationary and therefore must have the no-slip condition applied to them. To set this go to. and select the lines that make up the walls of

the duct. There are 6 of them:


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Click OK. In the window that appears set and . Leave VZ blank. The last step is to apply atmospheric pressure to the outlet of the duct. Go to

and select the right most vertical line and click OK. In the window thatappears, enter for the constant pressure value and click :


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Now the Modeling of the problem is done. The loads on the model will look like this:


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SOLUTION

Go to ANSYS . The following window appears. Change the first input field value to 1000, as shown. No other changes are needed. Click .


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Go to . Wait for ANSYS to solve the problem.


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POST-PROCESSING

Plotting the velocity distribution Go to . Then go to . The following window appears:

Select VSUM and click OK. The velocity distribution will look like this:


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Now go to and select Velocity. The vector plot looks like this:


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To view the recirculation zone in more detail it helps to animate the results. To do this go to


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. Select a few nodes in the entrance region (1) and select a few nodes in the recirculation region (2).Then click OK:

Now go to Select VX. The other default options are fine. Click OK


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ANSYS will then animate the flow. It will look similar to this (notice the recirculation region):


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Tutorial 3 Diverging Flow

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