Fluent Sloshing

Tutorial: Fuel Tank Sloshing

Introduction

The purpose of this tutorial is to investigate the free surface movement of liquid fuel in atank under varying acceleration scenarios and to determine the most suitable configurationof the fuel tank to ensure continuous fuel supply through the pick-up pipe.

Two configurations of the fuel tank are considered—tank with internal baffles and tankwithout internal baffles. You will compare the two configurations on the basis of liquidinterface and velocity vector plots generated for each case.

This tutorial demonstrates how to do the following:

• Set up and solve a transient problem using the pressure-based solver and the volumeof fluid (VOF) model.

• Define parameters specific to the non-iterative time advancement (NITA) scheme.

• Create a journal file to track the liquid interface with time.

• Execute the commands automatically to create images for postprocessing.

• Compare the two configurations on the basis of liquid interface and velocity vectorplots generated.

Prerequisites

This tutorial is written with the assumption that you have completed Tutorial 1 fromANSYS FLUENT 13.0 Tutorial Guide, and that you are familiar with the ANSYS FLUENTnavigation pane and menu structure. Some steps in the setup and solution procedure willnot be shown explicitly.

In this tutorial, you will use VOF model. If you have not used this model before, refer toSection 26.3, Setting Up the VOF Model in ANSYS FLUENT 13.0 User’s Guide.

Assuming that you are using a quad core single processor machine with a clock speed of 3.80GHz, this tutorial will take:

• Two hours to work through.

• Approximately 14 hours for the calculation.

c© ANSYS, Inc. February 9, 2011 1

Fuel Tank Sloshing

Problem Description

The tutorial considers two configurations of the fuel tank for comparison. Figure 1 showsthe tank with internal baffles. Figure 2 shows the tank without baffles. The tank undergoesan acceleration of 9.81 m/s2 in the positive X direction. As the tank accelerates in the +Xdirection, the liquid experiences an equal and opposite reaction in the −X direction. After1.5 seconds, the acceleration in the X direction stops and only gravity (in the −Z direction)acts on the liquid in the tank.

Figure 1: Schematic of Tank with Baffles

Figure 2: Schematic of Tank without Baffles

2 c© ANSYS, Inc. February 9, 2011

Fuel Tank Sloshing

Strategy

A prior analysis indicates that the pick-up pipe might not be completely submerged after0.45 seconds of acceleration and after 1.25 seconds of acceleration. An analysis of bothtank designs will be compared after 0.45 seconds and 1.25 seconds to confirm that the pick-up pipe in the tank without baffles is not submerged in fuel while the tank with baffleswill be analyzed to see if the baffles fix the problem and keep the pick-up pipe completelysubmerged in fuel. The tank with baffles will be analyzed first. Then, the baffles will beswitched from wall boundaries to interior boundaries and the tank without baffles will beanalyzed under the same conditions as the tank with baffles.

Setup and Solution: Configuration with Baffles

Preparation

1. Copy the file (ft11.msh.gz) to your working folder.

2. Use FLUENT Launcher to start the 3DDP version of ANSYS FLUENT.

For more information about FLUENT Launcher see Section 1.1.2 StartingANSYS FLUENT Using FLUENT Launcher in ANSYS FLUENT 13.0 User’s Guide.

The Display Options are enabled by default. Therefore, after you read in the mesh, itwill be displayed in the embedded graphics window.

Step 1: Mesh

1. Read the mesh file (ft11.msh).

File −→ Read −→Mesh...

As the mesh file is read, ANSYS FLUENT will report the progress in the console.

Step 2: General Settings

1. Define the solver settings.

General −→ Transient

2. Check the mesh (see Figure 3).

General −→ Check

ANSYS FLUENT will perform various checks on the mesh and will report the progressin the console. Make sure the minimum volume reported is a positive number.


Fuel Tank Sloshing

Figure 3: Mesh Display

3. Scale the mesh using a scale factor of 0.01 in the X, Y , and Z directions.

General −→ Scale...


Fuel Tank Sloshing

4. Reorder the domain until the bandwidth reduction is of the order of 1.0.

Mesh −→ Reorder −→Domain

Step 3: Models

1. Define the multiphase model.

(a) Select Volume of Fluid from the Model list.

(b) Enable the Implicit Body Force.

(c) Click OK to close the Multiphase Model dialog box.


Fuel Tank Sloshing

Step 4: Materials

Materials −→ Fluid −→ Create/Edit...

1. Copy kerosene-liquid from the database.

(a) Click the FLUENT Database... to open the FLUENT Database Materials dialogbox.

i. Select fluid from the Material Type drop-down list.

ii. Select kerosene-liquid from the FLUENT Fluid Materials list.

iii. Click Copy and close the FLUENT Database Materials dialog box.

(b) Click Create/Edit and close the Create/Edit Materials dialog box.

Step 5: Phases

(a) Define the primary phase.

Phases −→ phase-1-Primary Phase −→ Edit...


Fuel Tank Sloshing

i. Enter air for Name.

ii. Select air in the Phase Material drop-down list.

iii. Click OK to close the Primary Phase dialog box.

(b) Similarly, define the secondary phase, specifying kerosene-liquid for Name andselecting kerosene-liquid from the Phase Material drop-down list.

Step 6: Boundary Conditions

(a) Set the boundary conditions for inlet.

Boundary Conditions −→ inlet

i. Change the Type from velocity-inlet to wall.

This will open Wall dialog box.

ii. Retain the default settings and close the Wall dialog box.

(b) Set the boundary conditions for pick-out.

Boundary Conditions −→ pick-out

i. Retain the selection of mixture from the Phase drop-down list and click theEdit... button to open the Pressure Outlet dialog box.


Fuel Tank Sloshing

A. Retain 0 pascal for Gauge Pressure.

B. Click OK to close the Pressure Outlet dialog box.

ii. Select kerosene-liquid from the Phase drop-down list and click the Edit...button to open the Pressure Outlet dialog box.

A. Click the Multiphase tab and ensure that Backflow Volume Fraction is 0.

B. Click OK to close the Pressure Outlet dialog box.

Step 7: Operating Conditions

Boundary Conditions −→ Operating Conditions...

(a) Enable Gravity.

(b) Enter 0.25 m as the Reference Pressure Location for X, Y, and Z.

The reference pressure location should be selected where the fluid is primarilylighter. For this problem, it is selected at the center of the tank near the top (thetop boundary being the zmax surface of the tank).

(c) Set the Gravitational Acceleration in the X and Z directions to -9.81 m/s2.


Fuel Tank Sloshing

(d) Enable Specified Operating Density and retain the value of 1.225 kg/m3 for Op-erating Density.

(e) Click OK to close the Operating Conditions dialog box.

Step 8: Solution

1. Set the solution methods parameters.

Solution Methods

(a) Enable Non-Iterative Time Advancement.

(b) Retain the selection of First Order Implicit from the Transient Formulation drop-down list.

(c) Select Fractional Step from the Scheme drop-down list in the Pressure-VelocityCoupling group box.

(d) Select Green-Gauss Node Based from the Gradient drop-down list.

(e) Select Body Force Weighted from the Pressure drop-down list in the Spatial Dis-cretization group box.

(f) Retain the selection of First Order Upwind for Momentum and Geo-Reconstructfor Volume Fraction.


Fuel Tank Sloshing

2. Set the parameters that control the solution.

Solution Controls

(a) Set the Non-Iterative Solver Relaxation Factors for Pressure and Momentum to 0.6and 0.8, respectively.

3. Click Initialize to initialize the flow field.

Solution Initialization

4. Create an adaption register for patching.

Adapt −→Region...

(a) Set the Input Coordinates as shown in the following table:

Input Coordinates Values(X Min, X Max) (0, 0.5)(Y Min, Y Max) (0, 0.5)(Z Min, Z Max) (0, 0.08)

(b) Click Mark and close the Region Adaption dialog box.

5. Patch the liquid volume fraction.

Solution Initialization −→ Patch...

(a) Select kerosene-liquid from the Phase drop-down list.

(b) Select Volume Fraction from the Variable list.

(c) Enter 1 for Value.

(d) Select hexahedron-r0 from the Registers to Patch list.

(e) Click Patch and close the Patch dialog box.

6. Enable the plotting of residuals.

Monitors −→ Residuals −→ Edit...

(a) Enter 250 for Iterations to Plot.

(b) Click OK to close the Residual Monitors dialog box.

7. Enable the autosaving of data file after every 20 time step.

Calculation Activities

(a) Enter 20 for Autosave Every (Time Steps).


Fuel Tank Sloshing

(b) Click Edit... to open Autosave dialog box.

i. Enable Retain Only the Most Recent Files.

ii. Set the Maximum Number of Data Files to 2.

iii. Enter an appropriate file name (baffles-data-file.dat.gz).

iv. Click OK to close the Autosave dialog box.

Step 9: Animation Setup

1. Set the parameters for saving the hardcopy files.

File −→Save Picture...

(a) Select TIFF from the Format list.

(b) Select Color from the Coloring list and click Apply.

(c) Close the Save Picture dialog box.

2. Create a surface from the fluid-all zone.

Surface −→Zone...

(a) Select fluid-all from the Zone list and click Create.

(b) Close the Zone Surface dialog box.


Fuel Tank Sloshing

3. Open a graphics window for plotting the liquid interface.

Graphics and Animations −→ Options...

(a) Change the Active Window to 2.

(b) Click Set to set window 2 to be the active window.

(c) Close the Display Options dialog box.

4. Create an iso-surface for volume fraction of kerosene-liquid.

Surface −→Iso-Surface...

(a) Select Phases... and Volume fraction from the Surface of Constant drop-down lists.

(b) Select kerosene-liquid from the Phase drop-down list.

(c) Enter 0.5 for Iso-Values and vf05 for New Surface Name.

(d) Click Create and close the Iso-Surface dialog box.

5. Clip the fluid-all surface to the values of volume fraction of kerosene-liquid between0.5 and 1.

Surface −→Iso-Clip...


Fuel Tank Sloshing

(a) Select Phases... and Volume fraction from the Clip to Values of drop-down lists.

(b) Select kerosene-liquid from the Phase drop-down list.

(c) Select fluid-all from the Clip Surface list.

(d) Enter 0.5 and 1 for Min and Max, respectively.

(e) Enter clipf for New Surface Name.

(f) Click Clip and close the Iso-Clip dialog box.

6. Display the mesh.

Graphics and Animations −→ Mesh −→ Set Up...

(a) Disable Edges from the Options group box.

(b) Enable Faces from the Options group box.

(c) Deselect all the surfaces in the Surfaces selection list.

(d) Click Outline (below the Surface Name Pattern option).

(e) Select clipf and vf05 from the Surfaces list.

(f) Click Display and close the Mesh Display dialog box.

7. Manipulate the display using the Scene Description dialog box.

Graphics and Animations −→ Scene...

(a) Select clipf and vf05 from the Names list.


Fuel Tank Sloshing

(b) Click Display... in the Geometry Attributes group box to open the Display Proper-ties dialog box.

i. Set the sliders for Red, Green, and Blue to 0, 0, and 255, respectively, in theColors group box.

ii. Enable Lighting in the Visibility group box.

iii. Disable Edges, Lines, and Nodes in the Visibility group box.

iv. Enable Outer Faces in the Visibility group box.

v. Click Apply and close the Display Properties dialog box.

(c) Select all the surfaces except clipf and vf05 in the Names list.

(d) Click Display... in the Geometry Attributes group box to open the Display Proper-ties dialog box.


Fuel Tank Sloshing

i. Set the slider for Transparency to 80.

ii. Enable Lighting and Perimeter Edges in the Visibility group box.

iii. Disable Edges, Lines, and Nodes in the Visibility group box.

iv. Enable Outer Faces in the Visibility group box.

v. Click Apply and close the Display Properties dialog box.

(e) Close the Scene Description dialog box.

8. Set the orientation of the image in the graphics window as shown in Figure 4.

9. Save the view, View-1

Graphics and Animations −→ Views...

(a) Enter View-1 for the Save Name.

(b) Click Save to save the view.

(c) Close the Views dialog box.

10. Start writing the journal file (baffles.jou).

File −→ Write −→Start Journal...

(a) Display the mesh. Refer Step9: 6.

(b) Enable Light On and Headlight On.

Graphics and Animations −→ Lights...

(c) Set the view as View-1.


i. Select View-1 from the Views list.

ii. Click Apply and close the Views dialog box.

(d) Create a hardcopy of the fluid interface.


i. Click the Save... button to open the Select File dialog box.

ii. Enter image-%t.tif for Hardcopy File and click OK.

Using the character string %t in the file name, you can obtain automaticnumbering for the hardcopy files. ANSYS FLUENT appends the file namewith the time step number while saving the hardcopy files. This is usefulwhile creating an animation once the simulation is complete.

iii. Close the Save Picture dialog box.

(e) Stop writing to the journal file.

File −→ Write −→Stop Journal...

11. Set window 1 to be the active window.

Graphics and Animations −→ Options...


Fuel Tank Sloshing

12. Specify the commands to be executed at intervals in order to capture the images forpostprocessing.

Calculation Activities (Execute Commands)−→ Create/Edit...

(a) Set Defined Commands to 3.

(b) Define the commands as shown in the Execute Commands dialog box.

(c) Click OK to close the Execute Commands dialog box.

Step 10: Solution

1. Calculate the solution.

Run Calculation


Fuel Tank Sloshing

(a) Select Variable from the Time Stepping Method list.

(b) Enter 0.0001 s for Time Step Size and 10000 for Number of Time Steps.

(c) Click Settings... to open Variable Time Step Settings dialog box.


Fuel Tank Sloshing

(d) Enter 0.45 s for Ending Time.

(e) Enter 1e-05 s and 0.0025 s for Minimum Time Step Size and Maximum TimeStep Size, respectively.

(f) Enter 1.5 for Maximum Step Change Factor.

(g) Click OK.

(h) Save the case and data files (t=0.0s.cas/dat.gz).

(i) Click Calculate.

2. Read the journal file (baffles.jou) to create a hardcopy of the liquid interface att = 0.45 s.

3. Save the case and data files (t=0.45s.cas/date.gz).

4. Increase the Ending Time to 1.25 s and run the calculation.


6. Save the case and data files (t=1.25s.cas/dat.gz) .



9. Change the gravitation field.


(a) Enter 0 for Gravitational Acceleration in the X direction.

(b) Retain the previous settings of 0 and -9.81 for the Y and Z directions, respec-tively.

(c) Click OK to close the Operating Conditions dialog box.

10. Save the case and data files (t=1.5s.cas/dat.gz).



13. Save the case and data files (t=2.5s.cas/dat.gz).


Fuel Tank Sloshing

Setup and Solution: Configuration Without Baffles

1. Read the case file (t=0.00s.cas.gz).

2. Change the boundary condition Type for the baffle surfaces baf1, baf2, and baf3 fromwall to interior.

In the original mesh file, the baffles are denoted as wall surfaces.

3. Verify that the Gravitational Acceleration in theX, Y , and Z directions are -9.81 m/s2,0 m/s2, and -9.81 m/s2, respectively.

4. Initialize the solution and patch in the liquid kerosene level. For details, refer to Step8: 3–5.

5. Create a new journal file (no-baffles.jou) to track the liquid interface in the tankwith time.

File −→ Write −→Start Journal...

(a) Display the mesh.

Graphics and Animations −→ Mesh −→ Set Up...

i. Deselect all the surfaces in the Surfaces list.

ii. Select wall from the Surface Types list.

iii. Select clipf and vf05 from the Surfaces list.

iv. Click Display and close the Mesh Display dialog box.

(b) Enable Light On and Headlight On.

Graphics and Animations −→ Lights...

(c) Set the view as View-1.


i. Select View-1 from the Views list.

ii. Click Apply and close the Views dialog box.

(d) Create a hardcopy of the fluid interface.


i. Click the Save... button to open the Select File dialog box.

ii. Enter no-baffles-image-%t.tif for Hardcopy File and click OK.

iii. Close the Save Picture dialog box.

(e) Stop writing to the journal file.

6. Update the commands to be executed to include the journal file (no-baffles.jou)created.

Calculation Activities (Execute Commands)−→ Create/Edit...


Fuel Tank Sloshing

7. Update the autosave command for the data file to reflect a new file name and/orstorage folder.

Calculation Activities −→ Edit...

8. Set the iteration parameters.

Run Calculation −→ Settings...

(a) Enter 0.45 s for Ending Time.

(b) Enter 0.0001 s for Time Step Size and 10000 for Number of Time Steps.

(c) Save the case and data files at t = 0 s.

(d) Click Calculate.

9. Read the journal file (no-baffles.jou) to create a hardcopy of the liquid interfaceat t = 0.45 s.

10. Save the case and data files at t = 0.45 s.






16. Change the gravitation field.


(a) Enter 0 for Gravitational Acceleration in the X direction.

(b) Retain the previous settings of 0 and -9.81 for the Y and Z directions, respec-tively.

(c) Click OK to close the Operating Conditions dialog box.






Fuel Tank Sloshing

Postprocessing

1. Examine the liquid interface at times corresponding to 0.45 s and 1.25 s for bothconfigurations (see Figures 4, 5, 8, and 9).

2. Display velocity vectors at times corresponding to 0.45 s and 1.25 s for both config-urations (see Figures 6, 7, 10, and 11).

(a) Create an iso-surface to display velocity vectors.

Surface −→Iso-Surface...

i. Select Mesh... and Y-Coordinate in the Surface of Constant drop-down lists.

ii. Click Compute.

iii. Enter 0.25 for Iso-Values.

iv. Enter y=0.25 for New Surface Name and click Create.

v. Close the Iso-Surface dialog box.

(b) Display velocity vectors on y=0.25 m.

Graphics and Animations −→ Vectors

i. Enable Draw Mesh in the Options group box.

The Mesh Display dialog box will open.

A. Disable Faces and enable Edges in the Options group box.

B. Select Feature from the Edge Type list and retain the default value of 20for Feature Angle.

C. Deslect all the surfaces from the Surfaces list and click the Outline.

D. Select y=0.25 in addition to the previously selected surfaces.

E. Click Display and close the Mesh Display dialog box.

ii. Enter 5 for Scale and set Skip to 3.

iii. Select y=0.25 from the Surfaces list and click Display.

iv. Close the Vectors dialog box.

3. Run an external utility to produce an animation in MPEG or AVI format. Inspectthe animation to ensure that the baffles keep the pick-up pipe completely submergedin kerosene at all times from 0 seconds to 2.5 seconds.


Fuel Tank Sloshing

Figure 4: Liquid Interface at t = 0.45 for Tank with Baffles

Figure 5: Liquid Interface at t = 0.45 s for Tank Without Baffles


Fuel Tank Sloshing

Figure 6: Velocity Vectors at t = 0.45 s and y = 0.25 m for Tank with Baffles

Figure 7: Velocity Vectors at t = 0.45 s and y = 0.25 m for Tank Without Baffles


Fuel Tank Sloshing

Figure 8: Liquid Interface at t = 1.25 s for Tank with Baffles

Figure 9: Liquid Interface at t = 1.25 s for Tank Without Baffles


Fuel Tank Sloshing

Figure 10: Velocity Vectors at t = 1.25 s and y = 0.25 m for Tank with Baffles

Figure 11: Velocity Vectors at t = 1.25 s and y = 0.25 m for Tank Without Baffles

Summary

The liquid interface and velocity vector plots for the tank configurations with and withoutbaffles were examined. On comparing the two configurations, it was seen that the bafflescreated recirculation zones at the lower z plane where the intake of the pick-up pipe waslocated. This prevented kerosene from escaping the lower z plane, causing the pick-up pipeintake to be submerged in kerosene at all times. On the other hand, the images for theliquid interface at time 0.45 s (Figure 5) and 1.25 s (Figure 9) for the tank without bafflesshowed the existance of large scale sloshing. The pick-up pipe intake was not submerged inthe kerosene, preventing the continuous intake of kerosene.


Fluent Sloshing

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