CFX-FSI_14.5_WS05_T-Junction_1Way

© 2011 ANSYS, Inc. July 26, 20131 Release 14.5

14. 5 Release

Solving FSI Applications Using ANSYS Mechanical and ANSYS CFX

Workshop 5Thermal Stress Analysis in aT-Junction


Problem Description

A T-Junction model is subjected to the mixing of two fluids of differing temperatures

Cold Water (20oC)

Hot Water (80oC)

Warm Water


Problem Description

Junction is also subjected to fluid pressure

The goal is to perform a Thermal and Static Structural Analysis on the T-junction using the solution of the Conjugate Heat Transfer problem in CFX

Outline of procedure:

– Solve CHT problem in CFX

• This step has already been completed

– Transfer surface temperatures to a Steady-State Thermal (ANSYS) simulation and (re)solve solid temperatures

– Transfer fluid pressures to a Steady-State Structural (ANSYS) simulation

– Use temperatures from the Thermal solution as body loads in the Structural simulation

– Solve Static Structural case

– Solve an alternative workflow where the body temperatures from CFX are applied directly to a structural model, without using an intermediate Thermal system


Project Schematic

1. Open T_Junction.wbpj in Workbench

2. Drag Steady-State Thermal from the Analysis Systems toolbox and drop it onto the Solution cell of the Fluid Flow system (cell A5)

Links are created to share the

geometry and to transfer the

Fluid Flow Solution to the

Steady-State Thermal Setup.

The solution data will be

used as a thermal load in the

Steady-State Thermal

system.


Project Schematic

3. Now, select Static Structural and drag it onto Solution cell (B6) of Steady-State Thermal

• This will transfer the Mechanical thermal solution to the Mechanical structural model


Project Schematic

We also want the fluid pressure to be applied to the ANSYS structural model

4. Select the Solution cell (A5) of Fluid Flow and drag it onto Setup cell (C5) of Static Structural


Engineering Data

5. Double-click on Engineering Data under Steady-State Thermal

6. Right-click on Structural Steel as shown and select Duplicate

With the CFD model already completed, the thermal and structural analysis will be carried out in sequence.

The solid material used in the CFX analysis was Steel from the CFX Materials Library. The default material in ANSYS is Structural Steel. We need to make sure the material properties are consistent.


Add New Material

7. Rename Structural Steel 2 to “CFX Steel”

8. With CFX Steel selected, double-click on the Density value to edit it, then enter 7854 [kg m^-3]

9. Deselect the filter icon in the toolbar so that all the material properties are displayed

• Isotropic Thermal Conductivity has a value of 60.5 [W m^-1 C^-1] and Specific Heat has a value of 434 [J kg^-1 C^-1]. These are consistent with the values used in CFX.

10. Click Return to Project from the toolbar


Static Thermal Model

1. Double-click on Model under Steady-State Thermal

2. Expand Geometry and suppress the fluid body

3. Select NutsBolts under Geometry then change Assignment to CFX Steel

4. Select solid and change Assignment to CFX Steel


Global Mesh Sizing

5. Highlight Mesh in the Outline tree

6. In the details view expand Sizing and set Relevance Center to Medium

7. Right-click on Mesh and select Insert > Method

8. Right-click on the graphics background and choose Select All

9. In the details view click Apply

10. Change the Method to Tetrahedrons

11. Right-click on Mesh and select Generate Mesh


Cold and Hot End Boundaries

12. Select Units > Metric (m, kg, N, s, V, A)

13. Right-click on Steady-State Thermal (B5) in the tree view and select Insert > Temperature

14. Change Scoping Method to Named Selection

15. Pick wall_cold_end from the Named Selection drop-down

16. Set the Temperature Magnitude to 20ºC

– If the units are in K, select Celsius from the main Units menu

17. Insert another Temperature condition using the Named Selection wall_hot_end and a Temperature of 80ºC


External Convection Boundary

18. Right-click on Steady-State Thermal and select Insert > Convection


20. Select convection from the Named Selection drop-down

21. Enter Film Coefficient as 10 W/m2 ºC

22. Enter Ambient Temperature as 15 ºC


Imported Temperature Load

23. Under Steady-State Thermal right-click on Imported Load (Solution) and select Insert > Temperature


25. From the Named Selection drop-down list select interface_solid_side

26. From the CFD Surface drop-down list, select Fluid Solid Interface Side 2

– This is the CFX boundary associated with the solid side of the interface

27. Right-click on Imported Temperature and select Import Load

– View the imported temperature and the Imported Load Transfer Summary


Solve Static Thermal Model

28. Right-click on Steady-State Thermal (B5) and select Solve

29. Right-click on Solution and select Insert > Thermal > Temperature

30. Right-click on Solution and select Insert > Thermal > Total Heat Flux

31. Right-click on created Total Heat Flux object and select Evaluate All Results


Static Structural Analysis

Note that in the Project Schematic, the Steady-State Thermal analysis is now updated

In the Mechanical window Imported Load (Solution 1) under the Static Structural model can be seen. The temperature load from previously solved Thermal model will be automatically transferred to the Static Structural model

1. In the Project Schematic right-click and Refresh cell C5

• In Mechanical Imported Load (Solution) is nowadded to the Outline tree for the CFD load


Fixed Supports

2. Collapse the Steady-State Thermal branch of the Outline tree in Mechanical while working on the Static Structural analysis

3. Right-click on Static Structural and select Insert > Fixed Support

4. Select the three surfaces shown to the right in green then click Apply in the Geometry field

5. Right-click on Imported Load (Solution) and select Insert > Pressure

6. Set Scoping Method to Named Selection and pick interface_solid_side from drop down list

7. Set CFD Surface to Fluid Solid Interface Side 1

– This is the fluid side interface boundary

8. Right-click on Static Structural and select Solve


Total Deformation and Equivalent Stress

9. Right-click on Solution under Static Structural and select Insert > Deformation > Total

10. Right-click on Solution and select Insert > Stress > Equivalent

11. Right-click on Solution and select Evaluate All Results

12. Close the Mechanical window and save the project, but do not exit Workbench


Using a Body Temperature Import

Instead of importing a surface temperature from CFX, then re-solving the solid temperature field in Mechanical and transferring the temperature to a structural system, you can import the volumetric temperature directly from CFX to a structural system. This avoids the need for a Steady-State Thermal system. You will complete this alternative workflow next.

1. In the Project Schematic duplicate the Static Structural system by right-clicking on cell C5 and selecting Duplicate

• Performing Duplicate from the Setup cell retains the shared geometry and mesh



2. Select and delete the link between the Steady State Thermal system and the Copy of Static Structural system

3. Double-click the Setup cell (D5) to edit the Copy of Static Structural analysis, selecting Yes when asked to read the modified upstream data



Examine Static Structural 2 (D5) in the Outline tree. The Imported Pressure load and Fixed Support already exist from the previous structural analysis. Now add the Imported Body Temperature load. Start by creating a Named Selection for the solid parts; you’ll use this when importing the temperature load:

1. In the Outline tree, under Geometry, expand solid and select all 6 bodies named Part 2. Right-click and select Create Named Selection. Name the selection “solid”.



2. Right-click on Imported Load (Solution) and select Insert > Body Temperature

3. Set Scoping Method to Named Selection and pick solid from drop down list

4. Set CFD Domain to Solid

5. Right-click on Imported Body Temperatureand select Import Load

6. Examine the imported temperature and the Imported Load Transfer Summary after the import is complete

7. Right-click on Static Structural 2 (D5) and select Solve

– You can compare the solution to the previous method

8. Save the project and close Workbench

CFX-FSI_14.5_WS05_T-Junction_1Way

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