silo-2d

Tutorial: Silo Launch

Purpose

The purpose of this tutorial is to teach you how to set up and run a Moving DeformingMesh (MDM) problem.

Prerequisites

This tutorial assumes that you are familiar with the FLUENT interface, and that you havea have a good understanding of the basic setup and solution procedures. In this tutorial,you will use the dynamic mesh model. If you have not used this model before, refer to theFLUENT Dynamic Mesh Manual (www.fluentusers.com/fluent6/d o c/d o c f.htm).

Problem Description

An Intercontinental Ballistic Missile (ICBM) is being launched from its silo. The thrustof the missile is calculated from the UDF that is provided and Newton’s law is used todetermine the acceleration of the ICBM. The forces taken into account are the thrust, theviscous forces, and the gravity. The problem is set up in such a way, that there is no missilemotion for the first 0.1 seconds after the firing of the missile. Thus the computation is donein two steps, the first covering the time period between 0 and 0.1 seconds, and the next forthe period of the actual movement of the missile.

c© Fluent Inc. August 2, 2002 1

http://www.fluentusers.com/fluent6/doc/doc_f.htm

Silo Launch

Setup and Solution

Step 1: Grid

1. Start the 2D version of FLUENT and read the mesh file (silo-2d.msh.gz).

2. Check and display the grid.

Figure 1: Grid display

3. Examine the mesh (Zoom in on the mesh).

You will see a tetrahedral (tet) mesh in the area surrounding the missile and a hexa-hedral (hex) mesh on either side of the tetrahedral cell zone. The rest of the domainis meshed with tets. The main idea here is that we are going to move the whole tetzone surrounding the missile using rigid body motion. The layering algorithm is goingto add hex cells to the left of the missile and remove hex cells from the right of themissile.

Note: You will require to set up a sliding mesh interface so that the tet cells of thedomain can communicate with the hex cells of the layering zones.

2 c© Fluent Inc. August 2, 2002

Silo Launch

Step 2: Compile and Load the UDF

1. Copy the source file (silo.c) to your working directory.

2. Compile the UDF.

Define −→ User-Defined −→ Functions −→Compiled...

In FLUENT 6.1, you can compile and load the UDF in the same panel.

(a) In the Compiled UDFs panel, select Compile and add silo.c under Source Files.

By default, the Library Name will be set as libudf. Alternatively, you can specifya different library name of your choice.


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(b) Click Compile.

FLUENT creates the appropriate directory structure, makefiles, and compiles thecode for you. The progress of the compilation is shown in the FLUENT consolewindow. You can monitor the progress of the compilation for any linking errors.Alternatively, you can also view the log file with the compilation history that willbe created in the working directory.

3. Load the UDF.

(a) In the Compiled UDFs panel, select Load and click Open.

Step 3: Models

1. Select the Coupled solver with Explicit formulation and Unsteady time condition.

The MDM features are available only when an unsteady formulation is selected. Atthis point, only the 1st-Order Implicit formulation is available with the MDM.

2. In the Species Model panel, select Species Transport model.

3. Turn on the Inviscid turbulence model.

Step 4: Materials

1. Create a new fluid material named fxf.

(a) Select fluid for Material Type and air for Fluid Materials.

(b) Change the Name of the material from air to fxf and define the properties of fxfas follows:Parameter Value

Density ideal-gas

Cp 4000 j/kg-kMolecular Weight 50 kg/kgmol

(c) Retain the default values for the other parameters and click Change/Create.

Click No when asked to overwrite air.

2. Edit the mixture material, mixture-template.

(a) Modify the mixture species list.

i. Remove all the existing materials from the Selected Species list and add fxfand air in the following order:

A. air

B. fxf

Note: The panel will not allow you to remove all the materials from theSelected Species list. You will have to leave one material there which youcan remove after you insert air and fxf.

(b) Select ideal-gas for Density and click Change/Create.


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Step 5: Operating Conditions

1. Set the Operating Pressure to 0 Pa.

2. Retain the default values for the other parameters and click OK.

Step 6: Dynamic Mesh Setup

1. Define the Dynamic Mesh parameters.

Define −→ Dynamic Mesh −→Parameters...

(a) Click Dynamic Mesh.

(b) Deselect Smoothing and select Layering.

(c) Retain the default values of the other parameters.


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2. Define the zones for the Dynamic Mesh.

Define −→ Dynamic Mesh −→Zones...

(a) Create a rigid-body type zone.

i. Select fluid-14 under Zone Names, and Rigid Body under Type.

ii. Set the Motion UDF/Profile to missile 1dof and click Create.

(b) Create stationary type zones.

The fluid-14 zone contains both internal bot and inernal top zones. If you do notspecify these zones as stationary, then there would be no relative motion betweenthe missile and these zones.


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i. Select internal-bot for Zone Names and Stationary for Type.

ii. Set the value of Cell Height to 0.03048 m and click Create.

iii. Select internal-top for Zone Names and Stationary for Type.

iv. Set the value of Cell Height to 0.1524 m and click Create.

3. Define the non-conformal interface between the moving zone (fluid-14) and the sta-tionary zone (fluid-6).

(a) Select interface-in under Interface Zone 1 and interface-out under Interface Zone2.

(b) Under Grid Interface, type the name of the interface as SldInterface.

(c) Retain the default values for the other parameters.


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Step 7: Boundary Conditions

1. Set the boundary conditions for the nozzle-exit zone.

(a) Change the type for the nozzle-exit zone to mass-flow-inlet.

(b) Set the Mass Flow-Rate to 50 kg/s and Total Temperature to 2700 k.

(c) Retain the default values for the other parameters.

2. Set the boundary conditions for the far-field zone.

(a) Change the type for the far-field zone to pressure-outlet.

(b) Set the Gauge Pressure to 101325 and species mass fraction of air to 1.

(c) Retain the default values of the other parameters.

3. Change the type for axis-in and axis-out zones to axis.

4. Change the solver Space from 2D to Axisymmetric.

Step 8: Solution

1. Set the solution control parameters.

(a) Set the discretization scheme for Flow and air to First Order upwind.

(b) Set the Courant Number to 0.5 and retain the default values for the other pa-rameters.

2. Initialize the flow field.

(a) Set the value of Gauge Pressure and air Mass Fraction to 101352 pa and 1 respec-tively.

(b) Retain the default values of the other parameters and click Init.


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3. Create an animation sequence for the fxf mass fraction contour plot.

Solve −→ Animate −→Define...

(a) In the Solution Animation panel, change the Name to mass-frac and increase thenumber of Animation Sequences to 1.

(b) Increase the value for Every to 5 and select Time Step under When.

(c) Click Define... to define the animation sequence for fxf mass fraction.

i. In the Animation Sequence panel, select Contours for Display Type.

A. In the Contours panel, select Species... and Mass fraction of fxf from theContours Of drop-down lists.

B. Select Filled under Options. Retain the default values of the other pa-rameters.

C. Click Display and close the panel.

(d) Click OK in the Animation Sequence panel.

(e) Click OK in the Solution Animation panel.


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4. Start the calculation by requesting 10 timesteps.

(a) Set the Time Step Size to 0.01 s and Number of Time Steps to 10.

During this period of the calculation (0 to 0.1 seconds), there will be no motionof the missile .

5. Continue the calculation by requesting 100 timesteps.

(a) Set the Time Step Size to 0.001 s and Number of Time Steps to 100.

During this period of the calculation (0.1 to 0.2 seconds), the missile will be inmotion.

Step 9: Postprocessing

1. Play back the animation of the fxf mass fraction contour.

Solve −→ Animate −→Playback...

(a) Select mass-frac under Sequences and click the play button.

2. Display filled contours of Mach number at t=0.2 sec (Figure 2).

3. Display filled contours of mass fraction of fxf at t=0.2 sec (Figure 3).


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Figure 2: Mach Number contours at t=0.2 sec

Figure 3: Mass fraction of fxf contours at t=0.2 sec


silo-2d

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