Tutorial: Fuel Tank Sloshing Introduction The purpose of this tutorial is to investigate the free surface movement of liquid fuel in a tank under varying acceleration scenarios and to determine the most suitable configuration of 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 tank without internal baffles. You will compare the two configurations on the basis of liquid interface 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 volume of 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 vector plots generated. Prerequisites This tutorial is written with the assumption that you have completed Tutorial 1 from ANSYS FLUENT 13.0 Tutorial Guide, and that you are familiar with the ANSYS FLUENT navigation pane and menu structure. Some steps in the setup and solution procedure will not be shown explicitly. In this tutorial, you will use VOF model. If you have not used this model before, refer to Section 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 3.80 GHz, this tutorial will take: • Two hours to work through. • Approximately 14 hours for the calculation. c ANSYS, Inc. February 9, 2011 1
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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:
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.
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.
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.
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.
Graphics and Animations −→ Views...
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.
File −→Save Picture...
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.
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.
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.