ansys fluent simulation example pdf PDF

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a pdf that show you how to work on ansys fluent
for biggeners on fluent you can learn how to solve simple problem on cfd...

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Tank Flushing 1. Introduction This workshop teaches skills in the use of multiphase modeling, transient flow modeling, generating images, and preparing animations. Skills you will learn include: • Setting up a 2-phase simulation • Using tools (Patch) to control initialization • Preparing a transient animation • Using Solution Controls to modify the problem definition (turn off the valve)

2. Prerequisites This tutorial assumes that you are already familiar with the ANSYS Workbench interface and its project workflow. This tutorial also assumes that you have completed the first workshop and that you are familiar with the ANSYS Fluent tree and ribbon structure. Some steps in the setup and solution procedure will not be shown explicitly.

3. Problem Description In this workshop, you will model the filling and emptying of a water tank. The transient problem is solved as a multiphase (air/water) simulation, using the volume of fluid (VOF) multiphase model. An initial water level is set in the tank. The water supply is turned on for the first second of the simulation and then shut off for the rest of the simulation. The water level rises until water flows out the U-tube, generating a siphoning effect, which effectively empties the tank.

4. Setup and Solution 4.1. Starting Fluent and Loading a Mesh 1.

Copy the file tankflush.msh.gz to your working folder.

2.

Start ANSYS Fluent.

Note This workshop shows how to set up the simulation in standalone Fluent. You can also set up the simulation in Workbench as shown in the other workshops.

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1

Tank Flushing 3.

In the Fluent Launcher dialog box, select 3D under Dimension .

4.

Enable Double Precision under Options.

5.

Ensure that Display Mesh After Reading is enabled under Display Options.

6.

Click OK to open ANSYS Fluent.

Note IF HPC licenses are available, you can select Parallel under Processing Options and enter the number of processes.

7.

Load the mesh, tankflush.msh.gz. File

Read

Mesh...

4.2. Setting Up Domain 1.

Scale the mesh. Setting Up Domain

2.

2

Mesh

Transform

Scale...

a.

In the Scale Mesh dialog box, select cm from the Mesh Was Created In drop-down list.

b.

Select cm from the View Length Unit In drop-down list.

c.

Click Scale.

d.

Close the Scale Mesh dialog box.

Check the mesh. Release 17.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

Setup and Solution Setting Up Domain

Mesh

Check

Note Ensure that the minimum volume is not negative as ANSYS Fluent cannot begin a calculation when this is the case.

3.

Orient the view. Viewing

Display

Views...

a.

In the Views dialog box, select front from the list of Views.

b.

Click Apply.

c.

Click Auto Scale and then close the Views dialog box.

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3

Tank Flushing

Note The view can also be oriented by clicking on the +Z axis on the triad, in the lower right corner of the graphics window. Then click the Fit to Window toolbar.

icon in the graphics

4.3. Setting Up Physics In the steps that follow, you will select a solver and specify physical models, material properties, and zone conditions for your simulation using the Setting Up Physics ribbon tab. 1.

In the Solver group of the Setting Up Physics ribbon tab, select Transient from the Time group. Setting Up Physics

2.

Enable the realizable - turbulence model. Setting Up Physics a.

4

Solver

Models

Viscous...

In the Viscous Model dialog box, select k-epsilon from the Model list.

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Setup and Solution

3.

b.

Select Realizable from the k-epsilon Model group.

c.

Retain the other default settings, and click OK to accept the model and close the Viscous Model dialog box.

Enable the Volume of Fluid multiphase model. Setting Up Physics

Models

Multiphase...

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5

Tank Flushing

a.

In the Multiphase Model dialog box, select Volume of Fluid from the Model list.

b.

Ensure that Number of Eulerian Phases is set to 2.

c.

Ensure that Explicit is selected from the Formulation group box under Volume Fraction Parameters.

d.

In the Interface Modeling group box, ensure that the Type is set to Sharp.

Note In some applications, sharp resolution of the interface might not be necessary in all fluid zones. In such cases, using Dispersed Interface Modeling or a combination of Sharp and Dispersed modeling, can help to make the simulation more robust. In this application though, you want to achieve sharp resolution of the air-water interfaces, so choose Sharp under Interface Modeling.

6

e.

Enable Implicit Body Force from the Body Force Formulation group box.

f.

Click OK to set and close the Multiphase Model dialog box.

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Setup and Solution 4.

Add water to the list of materials. Setting Up Physics a.

b. 5.

Materials

Create/Edit...

In the Create/Edit Materials dialog box, click Fluent Database.... i.

From the list of Fluent Fluid Materials, select water-liquid (h2o).

ii.

Click Copy and then Close.

Close the Create/Edit Materials dialog box.

Define the phases. Setting Up Physics a.

Phases

List/Show All...

In the Phases dialog box, select phase-1 - Primary Phase and click Edit....

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Tank Flushing

b.

8

i.

In the Primary Phase dialog box, select water-liquid from the Phase Material drop-down list.

ii.

Enter water for Name.

iii.

Click OK to set and close the Primary Phase dialog box.

In the Phases dialog box, select phase-2 - Secondary Phase and click Edit....

i.

In the Secondary Phase dialog box, enter air for Name.

ii.

Ensure that air is selected from the Phase Material drop-down list.

iii.

Click OK to set and close the Secondary Phase dialog box.

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Setup and Solution

c.

d. 6.

Click Interaction... to define phase interactions.

i.

In the Phase Interaction dialog box, click the Surface Tension tab.

ii.

In the Surface Tension tab, enable Surface Tension Force Modeling.

iii.

Select constant under the Surface Tension Coefficients (n/m) drop-down list.

iv.

Enter 0.072 for Surface Tension Coefficients (n/m).

v.

Click OK to set and close the Phase Interaction dialog box.

Close the Phases dialog box.

Set the operating conditions. Setting Up Physics

Solver

Operating Conditions...

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9

Tank Flushing

a.

In the Operating Conditions dialog box, enable Gravity.

b.

In the Gravitational Acceleration group, enter -9.81 for Y (m/s2).

c.

Enable Specified Operating Density in the Variable-Density Parameters group box.

d.

Retain the default value of 1.225 for Operating Density (kg/m3).

Note The operating density should be set to the density of the lightest fluid in the domain when using the VOF model, or else an erroneous hydrostatic pressure distribution will occur.

e. 7.

Click OK to close the Operating Conditions dialog box.

Set the boundary conditions from the tree. a.

Set the boundary condition for the inlet mixture phase from the tree. Setup

10

Boundary Conditions

inlet (mass-flow-inlet)

Edit...

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Setup and Solution

b.

i.

In the Mass-Flow Inlet dialog box, select Normal to Boundary from the Direction Specification Method drop down list.

ii.

In the Turbulence group, from the Specification Method drop-down list, select Intensity and Hydraulic Diameter.

iii.

Retain the default of 5

iv.

Enter 2.1 for Hydraulic Diameter (cm).

v.

Click OK to close the Mass-Flow Inlet dialog box.

for Turbulent Intensity.

Set the boundary condition for the inlet water phase, from the tree. Setup

Boundary Conditions

inlet (mass-flow-inlet)

water

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Edit...

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Tank Flushing

c.

i.

In the Mass-Flow Inlet dialog box, retain the selection of Mass Flow Rate from the Mass Flow Specification Method drop down list.

ii.

Enter 0.2 for Mass Flow Rate (kg/s).

iii.

Click OK to close the Mass-Flow Inlet dialog box.

Similarly, set the Mass Flow Rate for inlet air phase to 0. Setup

d.

air

Edit...

Boundary Conditions

outlet (pressure-outlet)

Edit...

i.

In the Turbulence group, from the Specification Method drop-down list, select Intensity and Hydraulic Diameter.

ii.

Retain the default of 5

iii.

Enter 12.5 for Backflow Hydraulic Diameter (cm).

iv.

Click OK to close the Pressure Outlet dialog box.

for Turbulent Intensity.

Set the boundary condition for the outlet air phase from the tree. Setup

12

inlet (mass-flow-inlet)

Set the boundary condition for the outlet mixture phase from the tree. Setup

e.

Boundary Conditions

Boundary Conditions

outlet (pressure-outlet)

air

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Edit...

Setup and Solution

f.

i.

Enter 1 for Backflow Volume Fraction in the Multiphase tab.

ii.

Click OK to close the Pressure Outlet dialog box.

Copy the outlet boundary conditions to ambient. Setup

Boundary Conditions

outlet (pressure-outlet)

Copy...

i.

In the Copy Conditions dialog box, retain the selection of outlet from the From Boundary Zone list.

ii.

Retain selection of mixture from the Phase drop-down list.

iii.

Select ambient from the To Boundary Zones list.

iv.

Click Copy.

Note Click OK in the Question dialog box to confirm.

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13

Tank Flushing v.

Select air from the Phase drop-down list.

vi.

Ensure that ambient is selected from the To Boundary Zones list, and click Copy.

Note The Copy Conditions dialog box is a quick way of transferring common settings from one boundary to another. To Boundary Zones automatically displays boundaries of the same type as the From Boundary Zone selection.

vii. Close the Copy Conditions dialog box.

4.4. Solving In the steps that follow, you will set up and run the calculation using the Solving ribbon tab. 1.

Define the solution methods. Solving

14

Solution

Methods...

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Setup and Solution

2.

a.

In the Solution Methods task page, select PISO from the Scheme drop-down list in the PressureVelocity Coupling group.

b.

Retain the default settings for the rest.

Set the under-relaxation factors. Solving

Controls

Controls...

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Tank Flushing

3.

a.

In the Solution Controls task page, enter 0.3 for Momentum in the Under-Relaxation Factors group.

b.

Enter 0.5 for Turbulent Kinetic Energy and Turbulent Dissipation Rate.

Initialize the flow field using the Initialization group of the Solving ribbon tab. Solving

Initialization

Options...

This opens the Solution Initialization task page.

Note Initially, the tank is filled to a level of 6 cm with water. Here you will first initialize the flow solution, then create an adaption register and use the register to define the initial location of the liquid surface.

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Setup and Solution

a.

In the Solution Initialization task page, retain the default selection of Standard from the Initialization Methods group box.

b.

Select inlet from the Compute from drop-down lists.

c.

Enter 1 for air Volume Fraction in the Initial Values group.

d.

Click Initialize.

Note This will instruct the solver to fill the tank with air. The next step is to partially fill the tank with water, resulting in the proper initial condition.

4.

Define the region of the domain to be filled with liquid. Release 17.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information of ANSYS, Inc. and its subsidiaries and affiliates.

17

Tank Flushing Setting Up Domain

Adapt

Mark/Adapt Cells

Region...

a.

In the Region Adaption dialog box, enter -2.8 and 30 for X min (cm) and X Max (cm), respectively, in the group of Input Coordinates.

b.

Enter -1 and 6 for Y min (cm) and Y Max (cm), respectively.

c.

Enter -1 and 1 for Z min (cm) and Z Max (cm), respectively.

d.

Click Mark.

Note A message appears in the Fluent console informing you that 3716 cells have been marked.

e.

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To view the marked cells, click Manage.... i.

In the Manage Adaption Registers dialog box, select hexahedron-r0 from the list of Registers.

ii.

Click Options....

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Setup and Solution

iii.

A.

In the Adaption Display Options dialog box, enable Draw Mesh and Filled under Options.

B.

Enable Wireframe in the Refine and Coarsen group boxes.

C.

Click OK.

In the Manage Adaption Registers dialog box, click Display. The marked cells will be displayed in the graphics window, showing the liquid distribution at time = 0.

Note You may need to zoom in (use the Fit to Window icon mesh was scaled since it was first displayed.

) because the

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19

Tank Flushing iv. f. 5.

Close the Manage Adaption Registers and the Mesh Display dialog box.

Close the Region Adaption dialog box.

Patch the initial solution into the adaption register. Solving

Initialization

Patch...

a.

In the Patch dialog box, select air from the Phase drop-down list.

b.

Select Volume Fraction from the Variable list.

Note The specialized Volume Fraction Patch Options are not necessary for this problem.

6.

c.

Retain 0 for Value.

d.

Select hexahedron-r0 from the list of Registers to Patch.

e.

Click Patch and close the Patch dialog box.

Check the initial contours. Postprocessing

20

Graphics

Contours

Edit...

a.

To add a new graphics window to display the contours, right-click the existing tab at the top of the graphics window and select New Window.

b.

In the Contours dialog box, enable Filled.

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Setup and Solution c.

Select Phases... and Volume Fraction from the Contours of drop-down lists.

Note In multiphase problems, it is recommended to display contours of volume fraction to confirm the correct initial condition before beginning to iterate.

7.

d.

Retain the sel...