Carnegie Mellon

Mechanical Engineering

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FEM/ANSYS

## F3 Pipe Network

Fluid #3: Analyzing Flow in a System of Pipes USING FLOTRAN

Introduction: In this example you will model a system of pipes filled with water.

Physical Problem: Compute and plot the velocity distribution in the pipe system shown in the figure.

Problem Description:

·         The shape of the pipe grid is shown in the figure.  (Each point is spaced evenly at 0.33m)

Objective:
 To plot the velocity profile within the pipe. To graph the variation of velocity out the bottom pipe.

You are required to hand in print outs for the above.

Figure:

STARTING ANSYS

·         Click on ANSYS in the programs menu.

·         Select Interactive.

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

·         Click on Run.

MODELING THE STRUCTURE

 Go to the ANSYS Utility Menu Click Workplane>WP Settings The following window comes up

·         Check the Cartesian and Grid Only buttons

·         Enter the values shown in the figure above.

·         Go to the ANSYS Main Menu

·         In this problem we will model the pipe grid and then apply fluid flow to it.

·         Click Preprocessor>-Modeling-> and create the pipe grid as shown below.

·         Hint: You can use key points and then create the area

The modeling of the problem is done.

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, make sure the first two input fields read Constant, and then click on OK.  Another box will appear.  Fill in the values as shown below, then click 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 1000 to set the density of Water. Click OK.

·         Now choose CFD>Viscosity. The following window appears:

·         Fill in 1 to set the viscosity of Water. Click OK

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

MESHING:

DIVIDING THE CHANNEL INTO ELEMENTS:

·         Go to Preprocessor>Meshing>Size Cntrls>ManualSize>Global>Size. In the window that comes up type 0.025 in the field for 'Element edge length'.

·         Click on OK. Now when you mesh the figure ANSYS will automatically create a mesh, whose elements have a edge length of 0.025 m.

·         Now go to Preprocessor>Meshing>Mesh>Areas>Free. Click Pick All. The mesh will look like the following.

BOUNDARY CONDITIONS AND CONSTRAINTS

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

·                                             Enter 0.5 in the VX value field and click OK. The 0.5 corresponds to the velocity of 0.5 meters per second of air flowing into the pipe grid.

·                                             Repeat the above and set the velocity into the upper pipe as -1 meter/second.  This is because the flow is traveling to the left, or the negative direction.

·                                             Then, set the Velocity to ZERO along all of the edges of the pipes.  This is because of 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 bottom pipe outlet and click OK.

·                                             Once all the Boundary Conditions have been applied, the pipe grid will 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 50, 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:

·                     Next, go to Main Menu>General Postproc>Plot Results>Vector Plot>Predefined. The following window will appear:

·                     Select OK to accept the defaults.  This will display the vector plot of the velocity gradient.