tut07

8/10/2019 tut07

1/34

Tutorial 7. Using a Non-Conformal Mesh

Introduction

Film cooling is a process that is used to protect turbine vanes in a gas turbine engine fromexposure to hot combustion gases. This tutorial illustrates how to set up and solve a filmcooling problem using a non-conformal mesh. The system that is modeled consists ofthree parts: a duct, a hole array, and a plenum. The duct is modeled using a hexahedralmesh, and the plenum and hole regions are modeled using a tetrahedral mesh. These twomeshes are merged together to form a hybrid mesh, with a non-conformal interfaceboundary between them.

Due to the symmetry of the hole array, only a portion of the geometry is modeled inANSYS FLUENT, with symmetry applied to the outer boundaries. The duct contains ahigh-velocity fluid in streamwise flow (Figure7.1). An array of holes intersects the ductat an inclined angle, and a cooler fluid is injected into the holes from a plenum. Thecoolant that moves through the holes acts to cool the surface of the duct, downstream ofthe injection. Both fluids are air, and the flow is classified as turbulent. The velocity andtemperature of the streamwise and cross-flow fluids are known, and ANSYS FLUENT isused to predict the flow and temperature fields that result from convective heat transfer.

This tutorial demonstrates how to do the following:

Merge hexahedral and tetrahedral meshes to form a hybrid mesh.

Create a non-conformal mesh interface.

Model heat transfer across a non-conformal interface with specified temperatureand velocity boundary conditions.

Calculate a solution using the pressure-based solver.

Plot temperature profiles on specified isosurfaces.

Prerequisites

This tutorial is written with the assumption that you have completed Tutorial 1, andthat 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.

Release 12.0 c ANSYS, Inc. March 12, 2009 7-1
http://tut01.pdf/

8/10/2019 tut07

2/34

Using a Non-Conformal Mesh

Problem Description

This problem considers a model of a 3D section of a film cooling test rig. A schematicof the problem is shown in Figure 7.1. The problem consists of a duct, 49 in long,with cross-sectional dimensions of 0.75 in 5 in. An array of uniformly spaced holes islocated at the bottom of the duct. Each hole has a diameter of 0.5 inches, is inclined at

35 degrees, and is spaced 1.5 inches apart laterally. Cooler injected air enters the systemthrough the plenum having cross-sectional dimensions of 3.3 in 1.25 in.

Only a portion of the domain needs to be modeled because of the symmetry of thegeometry. The bulk temperature of the streamwise air (T) is 450 K, and the velocityof the air stream is 20 m/s. The bottom wall of the duct that intersects the hole arrayis assumed to be a completely insulated (adiabatic) wall. The secondary (injected) airenters the plenum at a uniform velocity of 0.4559 m/s. The temperature of the injectedair (Tinject) is 300 K. The properties of air that are used in the model are also mentionedin Figure7.1.

8= 450 KT

8= 450 KT

35

0.5 in

= 0.000017894 kg/ms

inject = 300 KT

= 1006.43 J/kgKCp

inject = 300 KT

z

x

Hole1

Plenum1

Hole2

Plenum2

9.5 in

0.5 in 0.5 in

5 in

3.3 in

v = 20 m/s

xy

24 in

0.75 in

TOP VIEW

1.25 in

1.25 in

FRONT VIEWv = 0.4559 m/s v = 0.4559 m/s

49 in

Figure 7.1: Schematic of the Problem

7-2 Release 12.0 c ANSYS, Inc. March 12, 2009

8/10/2019 tut07

3/34


Setup and Solution

Preparation

1. Download non_conformal_mesh.zipfrom theUser Services Center to your workingfolder (as described in Tutorial1).

2. Unzip non_conformal_mesh.zip.

The filesfilm hex.mshandfilm tet.mshcan be found in the non conformal meshfolder created after unzipping the file.

3. Use FLUENT Launcher to start the 3D version ofANSYS FLUENT.

For more information about FLUENT Launcher, see Section1.1.2in the separateUsers Guide.

Note: TheDisplay Options are enabled by default. Therefore, once you read in themesh, it will be displayed in the embedded graphics windows.

Step 1: Mesh

1. Read the hex mesh file film hex.msh.

File Read Mesh...

2. Append the tet mesh file film tet.msh.

Mesh Zone Append Case File...

TheAppend Case File... functionality allows you to combine two mesh files into one

single mesh file.3. Check the mesh.

General Check

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

http://../ug/flug.pdfhttp://www.fluentusers.com/

8/10/2019 tut07

4/34


4. Scale the mesh and change the unit of length to inches.

General Scale...

(a) Make sure that Convert Units is selected in the Scaling group box.

(b) Select in from the Mesh Was Created In drop-down list by first clicking thedown-arrow button and then clicking the in item from the list that appears.

(c) ClickScale to scale the mesh.

Domain Extents will continue to be reported in the default SI unit of meters.

(d) Select in from the View Length Unit In drop-down list to set inches as the

working unit for length.(e) Close the Scale Mesh dialog box.

5. Check the mesh.

General Check

Note: It is a good idea to check the mesh after you manipulate it (i.e., scale,convert to polyhedra, merge, separate, fuse, add zones, or smooth and swap.)This will ensure that the quality of the mesh has not been compromised.

6. Display an outline of the 3D mesh.

General Display...

(a) Retain the default selections in theSurfaceslist.

(b) ClickDisplay.

(c) Close the Mesh Display dialog box.


8/10/2019 tut07

5/34


7. Manipulate the mesh display to obtain a front view as shown in Figure7.2.

Graphics and Animations Views...

(a) Select frontin the Views list.

(b) ClickApply.

(c) Close the Viewsdialog box.

Y

XZ

MeshFLUENT 12.0 (3d, dp, pbns, lam)

Figure 7.2: Hybrid Mesh for Film Cooling Problem


8/10/2019 tut07

6/34


8. Zoom in using the middle mouse button to view the hole and plenum regions(Figure7.3).

Figure 7.3: Hybrid Mesh (Zoomed-In View)

In Figure 7.3, you can see the quadrilateral faces of the hexahedral cells that areused to model the duct region and the triangular faces of the tetrahedral cells thatare used to model the plenum and hole regions, resulting in a hybrid mesh.

Extra: You can use the right mouse button to check which zone number corre-sponds to each boundary. If you click the right mouse button on one of theboundaries in the graphics window, its zone number, name, and type will beprinted in theANSYS FLUENT console. This feature is especially useful whenyou have several zones of the same type and you want to distinguish betweenthem quickly.


8/10/2019 tut07

7/34


Step 2: General Settings

General

1. Retain the default solver settings.

Step 3: Models

Models

1. Enable heat transfer by enabling the energy equation.Models Energy Edit...

(a) ClickOK to close the Energydialog box.


8/10/2019 tut07

8/34


2. Enable the standard k-turbulence model.

Models Viscous Edit...

(a) Select k-epsilon (2 eqn) in the Model list.

TheViscous Model dialog box will expand to show the additional input optionsfor thek- model.

(b) Retain the default settings for the remaining parameters.

(c) ClickOK to close the Viscous Model dialog box.


8/10/2019 tut07

9/34


Step 4: Materials

Materials

1. Define the material properties.

Materials Fluid Create/Edit...

(a) Retain the selection ofair from the FLUENT Fluid Materials drop-down list.

(b) Select incompressible-ideal-gas law from the Densitydrop-down list.

The incompressible ideal gas law is used when pressure variations are smallbut temperature variations are large. The incompressible ideal gas option fordensity treats the fluid density as a function of temperature only. If the abovecondition is satisfied, the incompressible ideal gas law generally gives better

convergence compared to the ideal gas law, without sacrificing accuracy.

(c) Retain the default values for all other properties.

(d) Click Change/Create and close theCreate/Edit Materials dialog box.


8/10/2019 tut07

10/34


Step 5: Operating Conditions

Boundary Conditions Operating Conditions...

1. Retain the default operating conditions.

2. ClickOK to close the Operating Conditions dialog box.

For theincompressible-ideal-gas lawselected here for air, the constant pressure usedfor the density calculation is theOperating Pressure specified in this dialog box. So,make sure that theOperating Pressure is close to the mean pressure of the domain.


8/10/2019 tut07

11/34


Step 6: Cell Zone Conditions

Cell Zone Conditions

1. Set the conditions for the fluid in the duct (fluid-9).

Cell Zone Conditions fluid-9 Edit...

(a) Change the Zone Name from fluid-9to fluid-duct.

(b) Retain the default selection ofair from the Material Name drop-down list.

(c) ClickOK to close the Fluid dialog box.

2. Set the conditions for the fluid in the first plenum and hole (fluid-8).

Cell Zone Conditions fluid-8 Edit...

(a) Change the Zone Name from fluid-8to fluid-plenum1.



3. Set the conditions for the fluid in the second plenum and hole ( fluid-9.1).Cell Zone Conditions fluid-9.1 Edit...

(a) Change the Zone Name from fluid-9.1 to fluid-plenum2.




8/10/2019 tut07

12/34


Step 7: Boundary Conditions

Boundary Conditions

1. Set the boundary conditions for the streamwise flow inlet (velocity-inlet-1).

Boundary Conditions velocity-inlet-1 Edit...

(a) Change the Zone Name from velocity-inlet-1to velocity-inlet-duct.

(b) Enter 20 m/s for the Velocity Magnitude.(c) Select Intensity and Hydraulic Diameter from the Specification Method drop-

down list in the Turbulencegroup box.

(d) Enter 1% and 5 in for the Turbulent Intensity and the Hydraulic Diameter,respectively.

(e) Click the Thermal tab and enter 450 K for the Temperature.

(f) ClickOK to close the Velocity Inlet dialog box.


8/10/2019 tut07

13/34


2. Set the boundary conditions for the first injected stream inlet (velocity-inlet-5).


(a) Change theZone Namefrom velocity-inlet-5to velocity-inlet-plenum1.

(b) Enter 0.4559m/s for the Velocity Magnitude.

(c) Select Intensity and Viscosity Ratio from the Specification Method drop-downlist in the Turbulence group box.

(d) Enter 1% for Turbulent Intensity and retain the default setting of 10 for Tur-bulent Viscosity Ratio.

(e) Click the Thermal tab and retain the setting of 300 K for Temperature.

(f) ClickOK to close the Velocity Inlet dialog box.

In the absence of any identifiable length scale for turbulence, the Intensity and Vis-cosity Ratio method should be used.

For more information about setting the boundary conditions for turbulence, seeChapter12 in the separateUsers Guide.

http://../ug/flug.pdf

8/10/2019 tut07

14/34


3. Copy the boundary conditions set for the first injected stream inlet.

Boundary Conditions velocity-inlet-plenum1 Copy...

(a) Select velocity-inlet-plenum1in the From Boundary Zone selection list.

(b) Select velocity-inlet-6 in the To Boundary Zones selection list.

(c) ClickCopy.

A Warning dialog box will open, asking if you want to copy velocity-inlet-plenum1 boundary conditions to (velocity-inlet-6). ClickOK.

(d) Close the Copy Conditions dialog box.

! Copying a boundary condition does not create a link from one zone to

another. If you want to change the boundary conditions on these zones,you will have to change each one separately.


8/10/2019 tut07

15/34


4. Set the boundary conditions for the second injected stream inlet ( velocity-inlet-6).


(a) Change theZone Namefrom velocity-inlet-6to velocity-inlet-plenum2.

(b) Verify that the boundary conditions were copied correctly.

(c) ClickOK to close the Velocity Inlet dialog box.


8/10/2019 tut07

16/34


5. Set the boundary conditions for the flow exit (pressure-outlet-1).

Boundary Conditions pressure-outlet-1 Edit...

(a) Change theZone Namefrom pressure-outlet-1to pressure-outlet-duct.

(b) Retain the default setting of 0 Pa for Gauge Pressure.

(c) Select Intensity and Viscosity Ratio from the Specification Method drop-downlist in the Turbulence group box.

(d) Enter 1% forBackflow Turbulent Intensityand retain the default setting of 10forBackflow Turbulent Viscosity Ratio.

(e) Click the Thermal tab and enter 450 K forBackflow Total Temperature.

(f) ClickOK to close the Pressure Outlet dialog box.


8/10/2019 tut07

17/34


6. Retain the default boundary conditions for the plenum and hole walls (wall-4 andwall-5).

Boundary Conditions wall-4 Edit...


8/10/2019 tut07

18/34


7. Verify that the symmetry planes are set to the correct type in the Boundary Condi-tionstask page.

Boundary Conditions

(a) Select symmetry-1in the Zone list.(b) Make sure that symmetryis selected from the Type drop-down list.

(c) Similarly, verify that the zones symmetry-5, symmetry-7, symmetry-tet1, andsymmetry-tet2are set to the correct type.

8. Define the zones on the non-conformal boundary as interface zones by changing theTypeforwall-1, wall-7, andwall-8 to interface.

The non-conformal mesh interface contains three boundary zones: wall-1, wall-7,and wall-8. wall-1 is the bottom surface of the duct, wall-7 andwall-8 represent theholes through which the cool air is injected from the plenum (Figure 7.4). These

boundaries were defined as walls in the original mesh files (film hex.msh andfilm tet.msh) and must be redefined asinterface boundary types.


8/10/2019 tut07

19/34


(a) Open theMesh Display dialog box.

General Display...

i. Selectwall-1, wall-7, andwall-8 from the Surfaces selection list.

Use the scroll bar to access the surfaces that are not initially visible in the

Mesh Display dialog box.Note: You may need to deselect all surfaces first by selecting the unshaded

icon to the far right of Surfaces.

ii. ClickDisplay and close theMesh Display dialog box.

(b) Display the bottom view.


i. Selectbottom in theViews list and clickApply.

ii. Close theViews dialog box.

Zoom in using the middle mouse button. Figure7.4 shows the mesh forthewall-1andwall-7 boundaries (i.e., hole-1). Similarly, you can zoom into see the mesh for thewall-1 andwall-8 boundaries (i.e., hole-2).

Figure 7.4: Mesh for the wall-1 and wall-7 Boundaries


8/10/2019 tut07

20/34


(a) Select wall-1in theZone list and selectinterfaceas the new Type.

Boundary Conditions

AQuestion dialog box will open, asking if it isOKto change the type ofwall-1fromwall to interface. ClickYes in theQuestion dialog box.

The Interface dialog box will open and give the default name for the newlycreated interface zone.

i. Change the Zone Name to interface-duct.

ii. ClickOK to close the Interface dialog box.

(b) Similarly, convert wall-7 and wall-8 to interface boundary zones, specifyinginterface-hole1 and interface-hole2 for Zone Name, respectively.


8/10/2019 tut07

21/34


Step 8: Mesh Interfaces

Mesh Interfaces

In this step, you will create a non-conformal mesh interface between the hexahedral andtetrahedral meshes.

Mesh Interfaces Create/Edit...

1. Selectinterface-hole1and interface-hole2in the Interface Zone 1 selection list.

! When one interface zone is smaller than the other, choose the smaller zone

as Interface Zone 1.

2. Select interface-duct from the Interface Zone 2 selection list.

3. Enter junction forMesh Interface.

4. ClickCreate.In the process of creating the mesh interface, ANSYS FLUENTwill create three newwall boundary zones: wall-24, wall-25, andwall-26.

wall-24 and wall-25 are the non-overlapping regions of theinterface-hole1 andinterface-zone2 zones that result from the intersection of theinterface-hole1,


8/10/2019 tut07

22/34


interface-hole2, and interface-ductboundary zones. They are listed underBound-ary Zone 1in theCreate/Edit Mesh Interfacesdialog box. These wall boundariesare empty, sinceinterface-hole1 andinterface-hole2 are completely containedwithin the interface-duct boundary.

wall-26is the non-overlapping region of the interface-ductzone that results from

the intersection of the three interface zones, and is listed underBoundary Zone2 in theCreate/Edit Mesh Interfaces dialog box.

You willnotbe able to display these walls.

! You need to set boundary conditions forwall-26(since it is not empty). In

this case, the default settings are used.

5. Close the Create/Edit Mesh Interfaces dialog box.

Step 9: Solution

1. Set the solution parameters.

Solution Methods

(a) SelectSecond Order Upwindfrom theMomentum,Turbulent Kinetic Energy,Tur-bulent Dissipation Rate, andEnergydrop-down lists in theSpatial Discretizationgroup box.


8/10/2019 tut07

23/34


2. Enable the plotting of residuals.

Monitors Residuals Edit...

(a) Make sure Plot is enabled in the Optionsgroup box.

(b) ClickOK to close the Residual Monitors panel.


8/10/2019 tut07

24/34


3. Initialize the solution.

Solution Initialization

(a) Select velocity-inlet-duct from the Compute from drop-down list.

(b) ClickInitialize.

4. Save the case file (filmcool.cas.gz).

File Write Case...


8/10/2019 tut07

25/34


5. Start the calculation by requesting 250 iterations.

Run Calculation

(a) Enter 250 for the Number of Iterations.

(b) ClickCalculate.

Note: During the first few iterations, the console reports that turbulent viscos-ity is limited in a couple of cells. The console should no longer display thismessage as the solution converges and the turbulent viscosity approachesmore reasonable levels.

The solution converges after approximately 125 iterations.

6. Save the case and data files (filmcool.cas.gz

and filmcool.dat.gz

).File Write Case & Data...

Note: If you choose a file name that already exists in the current folder, ANSYSFLUENTwill prompt you for confirmation to overwrite the file.


8/10/2019 tut07

26/34


Step 10: Postprocessing

1. Reset the view to the default view if you changed the default display of the mesh.


(a) ClickDefaultin theActionsgroup box and close the Viewsdialog box.

2. Display filled contours of static pressure (Figure 7.5).

Graphics and Animations Contours Set Up...


8/10/2019 tut07

27/34


(a) Enable Filled in theOptions group box.

(b) Make sure Pressure... and Static Pressure are selected from the Contours ofdrop-down lists.

(c) Select interface-duct,interface-hole1,interface-hole2,symmetry-1,symmetry-tet1,symmetry-tet2, wall-4, andwall-5 in the Surfaces selection list.

Use the scroll bar to access the surfaces that are not initially visible in theContours dialog box.

(d) ClickDisplayin the Contoursdialog box.

Contours of Static Pressure (pascal)FLUENT 12.0 (3d, pbns, ske)

1.69e+0

1.57e+0

1.45e+0

1.33e+0

1.21e+0

1.09e+0

9.72e+01

8.53e+01

7.33e+01

6.13e+01

4.93e+01

3.73e+01

2.54e+01

1.34e+01

1.40e+0

-1.06e+0

-2.26e+0

-3.45e+0

-4.65e+0

-5.85e+0

-7.05e+0

Y

XZ

Figure 7.5: Contours of Static Pressure

The maximum pressure change (see Figure7.5) is only 239 Pa. Compared toa mean pressure of 1.013e5 Pa, the variation is less than 0.3%, and thus theuse of the incompressible ideal gas law is appropriate.

(e) Zoom in on the view to display the contours at the holes (Figures7.6and7.7).

Note the high/low pressure zones on the upstream/downstream sides of thecoolant hole, where the jet first penetrates the primary flow in the duct.


8/10/2019 tut07

28/34


Figure 7.6: Contours of Static Pressure at the First Hole

Figure 7.7: Contours of Static Pressure at the Second Hole


8/10/2019 tut07

29/34


3. Display filled contours of static temperature (Figures7.8and7.9).

Graphics and Animations Contours Set Up...

(a) Select Temperature... andStatic Temperature from the Contours ofdrop-downlists.

(b) Disable Auto Range in the Options group box so that you can change the

maximum and minimum temperature gradient values to be plotted.(c) Enter 300 forMin and 450 for Max.

(d) Disable Clip to Range in the Options group box.

(e) Make sure that, interface-duct,interface-hole1,interface-hole2,symmetry-1,symmetry-tet1,symmetry-tet2,wall-4, andwall-5, are selected from theSurfacesselectionlist.

(f) ClickDisplayand close the Contours dialog box.

(g) Zoom in on the view to get the display shown in Figure7.9.

Figures7.8and7.9clearly show how the coolant flow insulates the bottom ofthe duct from the higher-temperature primary flow.


8/10/2019 tut07

30/34


Figure 7.8: Contours of Static Temperature

Figure 7.9: Contours of Static Temperature (Zoomed-In View)


8/10/2019 tut07

31/34


4. Display the velocity vectors (Figure7.10).

Graphics and Animations Vectors Set Up...

(a) Make sure Velocity... and Velocity Magnitude are selected from the Color by

drop-down lists.(b) Enable Auto Range in the Options group box

(c) Enter 2 for the Scale.

This enlarges the displayed vectors, making it easier to view the flow patterns.

(d) Make sure that, interface-duct,interface-hole1,interface-hole2,symmetry-1,symmetry-tet1,symmetry-tet2,wall-4, andwall-5, are selected from theSurfacesselectionlist.

Use the scroll bar to access the surfaces that are not initially visible in thedialog box.

(e) ClickDisplayand close the Vectors dialog box.

(f) Zoom in on the view to get the display shown in Figure 7.10.

In Figure7.10, the flow pattern in the vicinity of the coolant hole shows the level ofpenetration of the coolant jet into the main flow. Note that the velocity field variessmoothly across the non-conformal interface.


8/10/2019 tut07

32/34


Figure 7.10: Velocity Vectors

5. Create an isosurface along a horizontal cross-section of the duct, 0.1 inches abovethe bottom, at y = 0.1 in.

Surface Iso-Surface...


8/10/2019 tut07

33/34


(a) SelectMesh... andY-Coordinatefrom the Surface of Constant drop-down lists.

(b) Enter 0.1 for Iso-Values.

(c) Enter y=0.1in for New Surface Name.

(d) ClickCreate.

(e) Close the Iso-Surfacedialog box.

6. Create an XY plot of static temperature on the isosurface created (Figure 7.11).

Plots XY Plot Set Up...

(a) Retain the default values in thePlot Direction group box.

(b) Select Temperature... and Static Temperature from the Y-Axis Function drop-down lists.

(c) Selecty=0.1in in the Surfacesselection list.

Scroll down using the scroll bar to accessy=0.1in.

(d) ClickPlot.

In Figure 7.11, you can see how the temperature of the fluid changes as thecool air from the injection holes mixes with the primary flow. The temperature

is coolest just downstream of the holes. You can also make a similar plot onthe lower wall to examine the wall surface temperature.

(e) Close the Solution XY Plot dialog box.


8/10/2019 tut07

34/34


Figure 7.11: Static Temperature at y=0.1 in

Summary

This tutorial demonstrated how the non-conformal mesh interface capability in ANSYSFLUENTcan be used to handle hybrid meshes for complex geometries, such as the filmcooling hole configuration examined here. One of the principal advantages of this ap-proach is that it allows you to merge existing component meshes together to create alarger, more complex mesh system, without requiring that the different components havethe same node locations on their shared boundaries. Thus, you can perform paramet-ric studies by merging the desired meshes, creating the non-conformal interface(s), and

solving the model. For example, in the present case, you can do the following:

Use a different hole/plenum mesh.

Reposition the existing hole/plenum mesh.

Add additional hole/plenum meshes to create aligned or staggered multiple holearrays.

Further Improvements

This tutorial guides you through the steps to reach an initial solution. You may be ableto obtain a more accurate solution by using an appropriate higher-order discretizationscheme and by adapting the mesh. Mesh adaption can also ensure that the solution isindependent of the mesh. These steps are demonstrated in Tutorial 1.
http://tut01.pdf/

Date post:	02-Jun-2018
Category:	Documents
Upload:	andre-oliveira
View:	214 times
Download:	0 times

tut07

Documents