premixed combustion tutorial fluent in conical chamber using zimont model

Tutorial: Premixed Combustion in a Conical Chamber Using

the Zimont Model

Introduction

The purpose of this tutorial is to provide guidelines and recommendations for setting upand solving a premixed gaseous mixture using the premixed combustion (Zimont) model.Both, adiabatic and non-adiabatic premixed combustion models will be used.

This tutorial demonstrates how to do the following:

• Use premixed combustion (Zimont) model.

• Use the adiabatic and non-adiabatic premixed combustion models.

• Set up and solve the case with appropriate solver settings.

• Postprocess the resulting data.

Prerequisites

This tutorial is written with the assumption that you have completed Tutorial 1 from theANSYS 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 the premixed combustion model. This tutorial does not coverthe mechanics of using this model. Instead, it focuses on the application of this modelto solve the problem. For more information refer to Chapter 18. Modeling PremixedCombustion in the ANSYS FLUENT 13.0 User’s Guide.

Problem Description

The conical combustor considered is shown in Figure 1. A small nozzle at the center ofthe combustor introduces the lean methane/air mixture (equivalence ratio = 0.6) at 60 m/sand 650 K. The high speed flow reverses direction in the combustor and exits through theco-axial outlet.

c© ANSYS, Inc. January 5, 2011 1

Premixed Combustion in a Conical Chamber Using the Zimont Model

Figure 1: Problem Schematic

The chemical reaction for an equivalence ratio of 0.6 is:

CH4 + 3.33(O2 + 3.76N2) = CO2 + 2H2O + 1.33O2 + 12.53N2

Some related parameters are as follows:

Table 1: Premixed Mixture Properties

Parameter ValueMass of air (for equivalence ratio 0.6) 2× (32 + 3.76× 28)/0.6 = 457.6Mass of 1 mole of fuel 16Mass fraction of fuel 0.0338Heat of combustion (j/kg) 3.84e+07Adiabatic Temperature (K) 1950Critical Strain Rate (1/s) 5000Laminar Flame Speed (m/s) 0.35

Preparation

1. Copy the files, conreac.msh to your working folder.

2. Use FLUENT Launcher to start the (2D) version of ANSYS FLUENT.

For more information about FLUENT Launcher see Section 1.1.2, Starting ANSYS FLU-ENT Using FLUENT Launcher in the ANSYS FLUENT 13.0 User’s Guide.

Note: The Display Options are enabled by default. Therefore, after you read in themesh, it will be displayed in the embedded graphics window.

2 c© ANSYS, Inc. January 5, 2011


Setup and Solution

Step 1: Mesh

1. Read the mesh file (conreac.msh).

File −→ Read −→Mesh...

Step 2: General Settings

1. Define the solver settings.

General

(a) Select Axisymmetric in the 2D Space list.

2. Check the mesh.

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.

3. Examine the mesh.



Figure 2: Mesh Display

Step 3: Models

Models

1. Define the viscous model.

Models −→ Viscous −→ Edit...

(a) Select the Standard k-epsilon (2 eqn) turbulence model.

(b) Click OK to close the Viscous Model dialog box.

2. Define the species model.

Models −→ Species −→ Edit...



(a) Select Premixed Combustion in the Model list.

(b) Retain the default selection of Adiabatic in the Premixed Combustion Model Op-tions list.

(c) Enter 0.637 for Turbulent Flame Speed Constant.

(d) Click OK to close the Species Model dialog box.

An Information dialog box will appear, reminding you to confirm the property valuesthat have been extracted from the database.

3. Click OK in the Information dialog box to continue.



Step 4: Materials

Create a new fluid material called premixed-mixture.

Materials −→ Fluid −→ Create/Edit...

1. Enter premixed-mixture for Name

2. Enter the values as shown in the Table 2.

Table 2: Premixed Mixture Material

Parameter ValueDensity (kg/m3) premixed-combustion

Adiabatic Unburnt Density (kg/m3) 1.2Adiabatic Unburnt Temperature (K) 650Adiabatic Burnt Temperature (K) 1950Laminar Flame Speed (m/s) 0.35Critical Rate of Strain (1/s) 5000

For the adiabatic model, the temperature is calculated from the temperature of theunburnt mixture and the adiabatic temperature of the burnt products. For more in-



formation, refer to the Section 9.6.1.1, Adiabatic Temperature Calculation in ANSYSFLUENT 13.0 Theroy Guide.

3. Click Change/Create and close the Create/Edit Materials dialog box.

When you click Change/Create, a Question dialog box will appear, asking you if airshould be overwritten. Click No to retain air and add the new material, premixed-mixture, to the list. The Create/Edit Materials dialog box will be updated to show thenew material name in the FLUENT Fluid Materials list.

Step 5: Cell Zone Conditions

Set the boundary conditions for fluid-6.

Cell Zone Conditions −→ fluid-6 −→ Edit...

1. Select premixed-mixture from the Material Name drop-down list.

2. Click OK to close the Fluid dialog box.

Step 6: Boundary Conditions

1. Set the boundary conditions for velocity-inlet-5.

Boundary Conditions −→ velocity-inlet-5 −→ Edit...



(a) Enter 60 m/s for Velocity Magnitude.

(b) Select Intensity and Length Scale from the Specification Method drop-down list.

(c) Enter 0.003 m for Turbulence Length Scale.

(d) Click OK to close the Velocity Inlet dialog box.

2. Set the boundary conditions for pressure-outlet-4.

Boundary Conditions −→ pressure-outlet-4 −→ Edit...



(a) Select Intensity and Length Scale from the Specification Method drop-down list.

(b) Enter 0.003 m for Backflow Turbulence Length Scale.

(c) Click the Species tab and enter 1 for Backflow Progress Variable.

(d) Click OK to close the Pressure Outlet dialog box.

3. Retain the default adiabatic boundary conditions for wall-1.

Step 7: Solution

1. Solve for flow and turbulence equations.

Solution Controls −→ Equations...

(a) De-select Premixed Combustion from the Equations list

(b) Ensure that Flow and Turbulence are selected.

(c) Click OK to close the Equations dialog box.

2. Initialize the solution.

Solution Initialization

(a) Select all-zones from the Compute from drop-down list.

(b) Click Initialize.

3. Save the case file (zimont.cas.gz).

File −→ Write −→Case...

4. Start the calculation by requesting 250 iterations.

Run Calculation −→ Calculate

The solution will converge in approximately 145 iterations.

5. Save the case and data files (zimont.cas/dat.gz).

File −→ Write −→Case & Data...



6. Solve using all the equations.


(a) Select Premixed Combustion from the Equations drop-down list.

(b) Click OK to close the Equations dialog box.

7. Patch progress variable.

Solution Initialization −→ Patch

(a) Select Progress Variable from the list of Variable.

(b) Enter 1 for Value.

(c) Select fluid-6 from Zones to Patch.

(d) Click Patch and close the Patch dialog box.

8. Request an additional 200 iterations or perform iterations until the solution converges(Figure 3).


Note: In the first iteration you will notice that the solution is converged. However itis not converged at this stage. Click Calculate again. Solution will converge inapproximately 80 additional iterations.

9. Save the case and data files, (zimont-ad.cas/dat.gz.

File −→ Write −→Case & Data...



Figure 3: Scaled Residuals

Step 8: Postprocessing

1. Display the velocity vectors in the domain (Figure 4).

Graphics and Animations −→ Vectors −→ Setup

(a) Sensure that Velocity is selected from the Vectors of drop-down list.

(b) Enter 10 for Scale and click Display.

(c) Close the Vectors dialog box.

Figure 4: Velocity Vectors



2. Display contours of stream function (Figure 5).

Graphics and Animations −→ Contours −→ Set Up...

(a) Select Velocity... and Stream Function from the Contours of drop-down lists andclick Display.

Figure 5: Contours of Stream Function

3. Display filled contours of mean progress variable (Figure 6).

(a) Enable Filled.

(b) Select Premixed Combustion... and Progress Variable from the Contours of drop-down lists and click Display.

Figure 6: Contours of Mean Progress Variable



4. Display filled contours of static temperature (Figure 7).

(a) Select Premixed Combustion... and Static Temperature from the Contours of drop-down lists and click Display.

Figure 7: Contours of Static Temperature

Step 9: Setup for Non-Adiabatic Premixed Combustion

1. Change the premixed combustion species model to Non-Adiabatic.

Models −→ Species −→ Edit...

(a) Select Non-Adiabatic from Premixed Combustion Model Options group box.

(b) Close the Species Model dialog box.

An information dialog box will open reminding you to confirm the property valuesthathave been extracted from the database. Click OK.

2. Modify the following properties for the premixed-mixture material:

Materials −→ premixed-mixture −→ Create/Edit...

Parameter ValueHeat of Combustion 3.85e+07Unburnt Fuel Mass Fraction 0.0338

For the non-adiabatic model, ANSYS FLUENT will solve an energy transport equationto account for heat losses or gains within the system. The temperature is calculated



from the heat of combustion and the fuel mass fraction. For more information, referto the Section 9.6.1.2, Non-Adiabatic Temperature Calculation in ANSYS FLUENT 13.0Theroy Guide.

3. Enter 650 K for Temperature in the Thermal tab for velocity-inlet-5.

Boundary Conditions −→ velocity-inlet-5 −→ Edit...

Step 10: Solution (Non-Adiabatic Premixed Combustion)

1. Solve for flow and turbulence equations.

(a) Select PRESTO! from the Pressure drop-down list in the Spatial Discretizationgroup box.

Solution Methods

(b) Select Flow and Turbulence from the Equations selection list.


2. Initialize the flow field and compute from all-zones.

Solution Initialization

3. Start the calculation by requesting 250 iterations.


Solution will converge in approximately 135 iterations.

4. Solve using all the equations.


(a) Select all the equations from the Equations selection list.

(b) Click OK to close the Equations dialog box.

5. Patch the progress variable to 1.

Solution Initialization −→ Patch...

6. Request another 150 iterations or perform iterations until the solution is converged(Figure 8).


The solution will converge in approximately 120 additional iterations.

7. Save the case and data files, (zimont-nonad.cas/dat.gz).



Figure 8: Scaled Residuals

Step 11: Postprocessing (Non-Adiabatic Premixed Combustion)

1. Display the velocity vectors in the domain with a scale factor of 10 (Figure 9).

Figure 9: Velocity Vectors



2. Display filled of stream function (Figure 10) with Filled from Options group box dis-abled.

Figure 10: Contours of Stream Function

3. Display filled contours of mean progress variable (Figure 11).

Figure 11: Contours of Mean Progress Variable



4. Display filled contours of static temperature (Figure 12).

Display contours of static temperature by selecting Temperature... and Static Temper-ature from the Contours of drop-down lists.

Figure 12: Contours of Static Temperature

Results

Postprocessing results can be used to study the application of the premixed combustionmodel in ANSYS FLUENT.

Summary

Application of premixed combustion model (Zimont model) in a premixed gaseous mixturecase has been demonstrated in this tutorial.


premixed combustion tutorial fluent in conical chamber using zimont model

Documents

c ansys

fluent launcher

tutorial guide

premixed gaseous mixture

d version of ansys fluent

theansys fluent

prerequisitesthis tutorial

zimont modelfigure