tutorial: simulating a 3d check valve using dynamic mesh ... · tutorial: simulating a 3d check...

© ANSYS, Inc. January 15, 2011 1

Tutorial: Simulating a 3D Check Valve Using Dynamic Mesh 6DOF Model And

Diffusion Smoothing

Introduction

The purpose of this tutorial is to demonstrate how to simulate a ball check valve with small displacement

using the dynamic mesh and 6DOF model in FLUENT. A pressure is applied at the valve inlet that pushes

the valve and causes it to move due to the fluid forces applied on the valve. This tutorial uses the

workbench workflow for solving the problem. As the displacement of the check valve ball in this case is

small, a smoothing approach is suitable for this problem. In this tutorial, the diffusion smoothing

algorithm is used. A pure hex mesh is used for this case since only smoothing is used. A dynamic mesh

UDF is used to specify the mass properties of the valve for the 6DOF model.

This tutorial demonstrates how to do the following:

Set up a problem using the dynamic mesh model.

Specify dynamic mesh modeling parameters.

Specify a rigid body motion zone.

Specify a deforming zone.

Use the 6DOF model.

Perform the calculation with residual plotting.

Post process using CFD-Post

Prerequisites

This tutorial assumes that you are familiar with the FLUENT interface and have completed Tutorial 1

from the FLUENT 13.0 Tutorial Guide. You should also be familiar with the dynamic mesh model. Refer

to Section 11.7: Steps in Using Dynamic Meshes in the FLUENT 13.0 User's Guide for more information

on the use of the dynamic mesh model.

Tutorial: Simulating a 3D Check Valve Using Dynamic Mesh 6DOF Model And Diffusion Smoothing


Problem Description

The problem considered is shown schematically in Figure 1. Check valves are commonly used to enforce

unidirectional flow of liquids and act as pressure-relieving devices. The check valve for this tutorial

contains a ball connected to a spring with a stiffness constant of 300 N/m. The ball is made of steel with a

density of 7800 kg/m3 and is represented as a cavity region in the mesh with a diameter of 4 mm. Initially

the center of mass of the ball is located at the coordinate point (0, 0.0023, 5e-05); this point is the spring

origin, and all forces that interact with the ball are assumed to pass through this point. The tank region,

located below the valve housing, is filled with Methanol (CH4O) at 25°C. High pressure from the liquid

at the tank opening (2 atm) causes the ball to move up, thus allowing the fluid to escape through the valve

to the atmosphere at an absolute pressure of 1 atm. The forces on the ball are: the force due to the spring

(not shown in the figure) and the force due to fluid flow. Gravity is neglected here for simplicity.

Figure 1: Problem schematic



The spring pushes the ball downward to oppose the force of the pressure when the ball is raised above its

initial position. The pressure variation causes the ball to oscillate along the Y-axis as a result of a dynamic

imbalance in the forces. The ball eventually stops oscillating when the forces acting on it are in

equilibrium.

In this tutorial the deformation of the ball itself is not modeled; mesh deformation is employed to modify

the mesh as the ball moves. A rigid body simulation is used to predict the motion of the ball, and will be

based on the forces that act on it (6DOF).

Preparation

1. Open Workbench 13.0

2. Unzip the project check_valve_diffusion_3d.wbpz by File -> Restore Archive

3. Double click on the Fluent Setup Cell

Figure 2: Workbench project page



4. From the FLUENT launcher, start FLUENT.

Setup and Solution

Step 1: Mesh

1. The mesh is automatically read into Fluent and displayed in the graphics window.

2. Note that if you are using standalone Fluent, you can read in the mesh from the File menu: File ->

Read -> Mesh. The mesh file for this project can be accessed by navigating the project files to

"check_valve_diffusion_3d_files\dp0\FFF\MECH". The mesh file is named FFF.msh.

Figure 3: Fluent window and mesh display

3. Check the mesh by clicking on Mesh -> Check

4. FLUENT will perform various checks on the mesh and report the progress in the console. Make

sure that the minimum volume reported is a positive number.



5. Change the pressure units to atm from Pa

(a) Define -> Units

(b) Pick pressure in the "Quantities" window

(c) Pick atm as the unit

(d) Close

6. Note that Most of the Fluent settings can be accessed by navigating the setup tree on the left in

the Fluent Window

Step 2: General Settings

Problem Setup -> General Settings

1. Enable time-dependent calculations.

(e) Select Transient from the Time list.



Figure 4: General settings

Step 3: Models

Problem Setup -> Models -> Viscous

1. Enable the standard k-epsilon model with standard wall functions.

Figure 5: Models options



Figure 6: Viscous models window

Step 4: Materials

Problem Setup -> Materials

1. Create/Edit -> Fluent Data Base

(a) Pick methyl-alcohol-liquid

(b) Copy, Close

2. Close the Materials panel.



Figure 7: Materials panel

Step 5: Cell Zone Conditions

Problem Setup -> Cell Zone Conditions

1. Pick each cell zone listed and click Create/Edit

2. In the pop up window, make sure that the material selected is methyl-alcohol-liquid and not air

Step 6: Boundary Conditions

Problem Setup -> Boundary Conditions

In this step, you will set the inlet and outlet conditions.

1. Define boundary conditions for the inlet zone.



(a) Pick the boundary named as "inlet" and switch the Type to pressure-inlet

(b) Enter 2(atm) to be the Gauge total pressure

(c) Switch the direction specification method to be Normal to Boundary

(d) Select Intensity and Viscosity Ratio from the Specification Method drop-down list

(e) In the Turbulence group box, set Turbulent Intensity to 5% and Turbulent Viscosity Ratio

to 10%.

(f) Click OK to close the Velocity Inlet panel.

2. Similarly pick the outlet zone and click Edit

(a) Select Intensity and Viscosity Ratio from the Specification Method drop-down list

(b) In the Turbulence group box, set Turbulent Intensity to 5% and Turbulent Viscosity Ratio

to 10%.

(c) Click OK to close the pressure outlet panel.

3. Close the Boundary Conditions panel.

Figure 8: Inlet boundary conditions panel



Step 7: Compile the UDF

Note that the tutorial project has the UDF libraries included. The UDF has been compiled in serial on

Windows 64 bit machine. To run the tutorial on any other hardware specification, it needs to be re-

compiled.

A 6DOF UDF is used in this example. The DEFINE_SDOF_PROPERTIES macro is used to assign the

mechanical properties of the check valve. The motion of the valve is automatically calculated by Fluent

from the forces acting on the valve. You will need a c-compiler installed on your machine to be able to

compile UDFs.

Define -> User Defined -> Functions -> Compiled

1. Click the Add... button in the Source Files group box.

2. The Select File dialog will open.

3. Browse to the folder "check_valve_diffusion_3d_files\dp0\FFF\Fluent". Select the file

check_valve_motion.c and click OK to close the Select File dialog.

4. Click Build to build the library.

5. FLUENT will set up the directory structure and compile the code. The compilation will be

displayed in the console.

6. Click Load to load the library.

7. Close the Compiled UDFs panel.



Figure 9: Compiled UDF panel

Step 8: Mesh Motion Setup

1. Enable dynamic mesh motion and specify the associated parameters.

(a) Problem Setup -> Dynamic Mesh

(b) Enable Dynamic Mesh in the Models group box.

(c) Enable Smoothing in the Mesh Methods group box and Six DOF in the Options.

(d) Make sure that the Layering and Remeshing options are disabled.

(e) Click on Mesh Method Settings to open the Mesh Method Settings panel. Switch method

to Diffusion in the Smoothing tab.

(f) Click OK to close the Dynamic Mesh Parameters panel.



Figure 10: Dynamic mesh settings

2. Specify the motion of the check valve ball



(a) Click on Create/Edit in the Dynamic Mesh Panel.

(b) Select ball from the Zone Names drop-down list.

(c) Retain the selection of Rigid Body in the Type list.

(d) Select spring_check_valve::libudf from the Six DOF UDF drop-down list.

(e) Enter Center of Gravity location of the ball as (X, Y, Z) = (0.0, 0.0023, 5.0e-5) m

(f) Make sure the Six DOF Options is turned to On

(g) Click Create.

Figure 11: Settings for 6DOF ball valve



(h) FLUENT will create the dynamic zone valve which will be available in the Dynamic

Zones list.

3. Specify the motion of the symmetry 1.

(a) Select symmetry1 from the Zone Names drop-down list.

(b) Select Deforming from the Type list.

(c) Click the Meshing Options tab and set the following parameters:

(d) Enable Smoothing and disable remeshing in the Methods group box.

(e) Retain the default settings for the remaining parameters.

(f) Click Create.

(g) FLUENT will create the dynamic zone axis1 which will be available in the Dynamic

Zones list.

4. Do the same for symmetry2Select axis2 from the Zone Names drop-down list.

5. Close the Dynamic Mesh Zones panel.

6. Save the project.

Step 9: Solution

In a dynamic mesh simulation, the mesh changes are saved in the case files. At any point in the solution,

to revert the mesh back to original settings and to start calculation from beginning, close Fluent and click

on the Settings cell again in the project page. This will re-launch Fluent with the original mesh but with

all the saved settings. To re-start a calculation, always launch Fluent from the Solution cell. This reads in

the latest Fluent case and data file.

1. Request saving of case and data files every 25 time steps.

(a) Solution -> Calculation Activities -> Autosave

(b) Enter 25 for both Autosave Case File Frequency and Autosave Data File Frequency.

Clicking on Edit makes more options available.

(c) Click OK to close the Autosave panel.



Note: Fluent case and data files can also be read by CFD-Post for post processing but in the interests of

minimizing hard disk space , you have the option to write out light weight files of only the variables that

you are interested in for Post processing by following these steps:Calculation Activities > Automatic

Export > Create > Solution Data Export. Choose file type to be CFD-Post compatible. Select Frequency,

give a file name, select variables to post process

2. Solution -> Solution Methods

(a) Switch P-V Coupling Scheme to Coupled

(b) Switch Spatial Discretization Scheme for Pressure to PRESTO!

3. Retain the default solution control parameters at Solution -> Solution Controls

4. Enable the plotting of residuals during the calculation.

(a) Solution -> Monitors -> Residual

(b) Enable Plot in the Options group box.

(c) Click OK to close the Residual Monitors panel.

5. Initialize the flow field

(a) Solution-> Solution Initialization -> Initialize

(b) Set TKE value to 0.1.

(c) Click Initialize and close the Solution Initialization panel.

6. Save the project. Saving the project after initialization saves the settings file and the first case file.

Any subsequent changes to the settings during the run will write out case files appended with an

integer number corresponding to the change in settings you make. Resetting any cell in the

Workbench project will clear all the corresponding files from the directory.

7. Run the calculation for 150 time steps.

(a) Solution -> Run Calculation -> Iterate

(b) Enter 5e-5 s for Time Step Size.

(c) Enter 150 for Number of Time Steps.

(d) Click Iterate.



(e) Close the Iterate panel.

Figure 12: Residual plot

Postprocessing

You have two options for post processing. One is to use the Fluent post processor Results -> Graphics and

Animations/ Plots/ Reports. The other is to use CFD-Post. When you are dealing with transient data and

wish to create animations/ plots, CFD-Post offers features that may not be available in Fluent Post. So

long as you have written out data files at a frequency, CFD-Post can read in those files and create

animations, transient monitors without pre-setting these at the beginning of your simulation.

For details on using Fluent Post, please refer tutorial X.

Step 1: Launch CFD-Post

1. Close Fluent and double click on the Results cell in workbench. This launches CFD-Post with the

last .cas and .dat file read in automatically.



1. Click on "z-axis" in the display window to see front view of geometry.

2. Click on the clock icon on the menu. This will show the transient sequence of files that

has been loaded.

(a) Double click on any Step to display results at that time step.

Figure 13: Time step selector to display results at any saved simulation time

Step 2: Display velocity contours:

1. Insert Contour from the menu. Insert -> Contour

2. Give a name to the contour

3. In the contour details, select location to be symmetry1 tank and symmetry1 valve.

4. Select variable to be velocity



5. Click apply. This displays the velocity contours in the display window.

Note: Other variable contours (e.g Static Pressure etc.) can be set up in similar fashion. As further

practice, please try setting up velocity vectors by Insert -> Vector. The Insert menu has also different

options such as inserting text, legends and so on. New planes or surfaces for display of data can be

created by Insert -> Location. Any feature (contours, vectors, particle tracks) that have been inserted can

be turned on or off in the display by clicking on the check box next to the feature.

Figure 14: Velocity contours at 1s of flow time

Step 3: Creating animations

6. We will animate the mesh deformation. For this, first uncheck the contours created in previous

step.



7. Display the mesh on symmetry1 tank and symmetry1 valve. For this, check the box next to the

required locations in the loaded data file boundaries displayed in the tree view on the left.

8. Double click on symmetry1 tank. This brings up the details panel on the left bottom corner of

CFD-Post.

9. In the "Render" tab check the box next to "Show Mesh Lines". This displays the mesh in

symmetry 1 tank.

10. Do the same for symmetry1 valve.



Figure 15: Displaying mesh on symmetry planes

11. Click on the animation icon. This brings up the animation panel.

12. Select Time steps as the object to animate.

13. You can adjust the slider to make the animation fast or slow.

14. Clicking on the downfacing arrow brings up a few more details.

15. Check the box next to "Save Movie".

16. Browse to the required folder and give a name.

17. Then click on the play button.

18. This animates the mesh motion and save it into a wmv file. The animation file format is flexible

and many options are available.



Figure 16: Animation panel in CFD-Post

19. Contours, iso-surfaces, streamlines etc. can be animated in similar fashion.

Step 4: Creating transient XY plots

1. Create a point on a node attached to the check valve

2. Insert -> Location -> Point

3. Check the box adjacent to the boundary called "ball" in the tree view of the loaded data file on the

left

Figure 17: Displaying the ball valve and creating a point



4. In the point details window, set method to be "XYZ" and click on the co-ordinates window

5. You can now pick your XYZ location with your mouse pointer on the 3D viewer. Select a point

on the Valve close to the top

6. Clicking "Apply" in the point details displays the nearest node location to the selected XYZ

location

7. Switch Domains to "valve"

8. Now, switch the method to Node Number and enter the node number obtained from previous

step. This will ensure that the point is hooked to the mesh node. If the node is displaced by mesh

motion, the point is displaced as well. Click "Apply"

Figure 18: Point details menu

9. From the Insert menu, select Insert -> Chart.

10. In the details of the chart, set type to be "XY-Transient or sequence" . Enter a title for the chart.

11. Go to the "Data Series" tab. Under Data Source, pick Point 1 as the location.



12. Under "Y Axis" tab, pick X as the plot variable and click apply

13. The transient variation of the node location defined by Point 1 is plotted on a chart in the chart

window.

Figure 19: Tracking the motion of the valve (point attachhed to node on valve) in x-

direction

Note: Instead of a point, create a line location. XY solution data can be plotted on the line to analyze

your result.

Step 5: Automatic Reports

1. Right click on the 3D viewer and select "Copy to New Figure". The figure is automatically

inserted into the automatically generated report.

2. Any charts that were created are also inserted automatically into the report.



3. Click on the Report viewer tab on the bottom to access the automatically generated report.

Step 6: Expressions

CFD-Post allows creation of expressions to evaluate quantitative data from flow results. The expressions

can also be used to create XY plot and creating tables.

1. Select the Expression tab on the top left.

2. Right click on Expressions and click on "New"

Figure 20: Creating expressions

3. Enter a name for the Expression

4. Right click on the blank details panel that opens up

5. This opens up the CEL expressions drop down list. All the accessible functions, expressions,

variables, boundary locations and constants are listed

6. Choose functions -> CFD-Post -> massFlow

7. The CEL syntax for massFlow is inserted as massFlow()@

8. With the mouse pointer resting after the @ symbol, Choose Locations -> outlet

9. The entire syntax for calculation mass flow at the boundary named as the outlet is

massFlow()@outlet



10. Click Apply to see the calculated value in the box

11. Expressions can be used in XY plots, tables and in creating custom variables.

Figure 21: Writing CEL expressions

Step 7: Custom Variables

1. Create another expression for velocity magnitude as sqrt(Velocity u^2+Velocity v^2+Velocity

w^2).

2. This can be done as in previous step by right click on the details window and selecting from the

menu that opens up. Flow variable names are listed under "Variables".



3. Go to the Variable tab

4. Right click in the window, click on New

5. Enter a name for the custom variable (e.g VelMag) > ok

6. In the details window, under Expressions select the expression for velocity magnitude that you

created

7. Apply

8. This creates a new flow variable called VelMag that can be used in contour plots and so on just

like any other flow variables.

Step 8: Creating Tables

1. Insert -> Table

2. This opens the table viewer

3. Click on any cell in the table. Entries in the table (text etc.) can be typed in the entry box that

appears.

4. Functions, expressions etc. can be inserted in the table by selecting relevant data from the drop

down lists that appear at the top.

Figure 22: Using the table viewer



Figure 23: Case comparison

Step 9: Case Comparison

(a) Go back to the 3D viewer and display the velocity contours.

(b) You may have to turn on the contour you inserted in Step 2.

(c) Now load one of the data files in the sequence again by File -> Load Results and

navigating to check_valve_diffusion_3d_file\dp0\FFF\Fluent and picking FFF-1-

000150.dat.gz

(d) Now you will see the two Cases listed in the tree view on the left as Case 1 and Case 2

(e) Double click on Case Comparison, which is the first item in the tree.



(f) In the Details menu that appears, you can now pick Case 1 and Case 2 as required. The

entire time history is available to pick.

(g) Double click on Step 150 for Case 1 and Step 50 for Case 2.

(h) Apply.

(i) This shows the contours plotted on Case 1, Case 2 and the difference between the two in

the viewer on the right.

Summary

In this tutorial, you used the diffusion smoothing option for the dynamic mesh feature in FLUENT. The

motion was limited to small distances. 6DOF model was used to calculate valve motion under the action

of fluid forces. Post processing is shown using CFD-Post to detail some of the features of the post

processing tool.

tutorial: simulating a 3d check valve using dynamic mesh ... · tutorial: simulating a 3d check...

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