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Transcript of Co Combustor
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Tutorial: Partially Premixed Combustion in a Co-axial
Combustor
Purpose
The purpose of this tutorial is to provide guidelines and recommendations for setting upand solving a reacting flow using the partially premixed combustion model.
Prerequisites
This tutorial assumes that you are familiar with the FLUENT interface and have a goodunderstanding of basic setup and solution procedures. Some steps will not be shown explic-itly.
In this tutorial, you will use the partially premixed combustion model. The partially pre-mixed model is based on both non-premixed (mixture-fraction based) and premixed (reac-tion progress variable based) combustion models. If you have not used these models before,it would be helpful to first refer to sections 15 and 16 ofFLUENT 6.2 Users Guide. Also, re-fer to Tutorial 13: Using the Non-Premixed Combustion Model in the FLUENT 6.2 Tutorial
Guide.
Problem Description
The coaxial combustor considered is shown in the following figure. A swirler at the centerof the combustor introduces the lean methane/air mixture (equivalence ratio=0.8) with anaxial velocity of 50 m/s and swirl velocity of 30 m/s. Pure air at an axial velocity of 10 m/sis introduced from the outer tube to stabilize the flame. The major species involved in thecombustion process are CH4, O2, CO2, CO, H2O, and N2.
Preparation
1. Copy the mesh file, par-premixed.msh.gz to the working directory.
2. Start FLUENT 2D.
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http://www.fluentusers.com/fluent/doc/ori/html/tg/main_pre.htmhttp://www.fluentusers.com/fluent/doc/ori/html/tg/main_pre.htmhttp://www.fluentusers.com/fluent/doc/ori/html/tg/node193.htmhttp://www.fluentusers.com/fluent/doc/ori/html/ug/main_pre.htmhttp://www.fluentusers.com/fluent/doc/ori/html/ug/node595.htmhttp://www.fluentusers.com/fluent/doc/ori/html/ug/node557.htm -
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
Figure 1: Schematic Figure
Setup and Solution
Step 1: Grid
1. Read the mesh file, par-premixed.msh.gz.
2. Check the grid.
Grid Check
3. Scale the grid to inches.
Grid Scale
4. Display the grid (Figure 2).
Display Grid...
5. Reorder the grid to speed up the computations.
Grid Reorder Domain
Do this step twice to get a bandwidth reduction in the order of 1.00.
Step 2: Models
1. Define Segregated solver for Axisymmetric Swirl space and Steady time condition.
Define Models Solver...
2. Enable the standard k-epsilon (2 eqn) turbulence model.
Define Models Viscous...
3. Select Partially Premixed Combustion as the Species Model.
Define Models Species Transport & Reaction...
(a) Enable Create Table option.
You can choose to skip the next step and read the pdf file, par-premixed.pdf.gz.
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
Z
Y
X
GridFLUENT 6.2 (axi, segregated, pdf7, ske)
Mar 03, 2005
Figure 2: Grid
Step 3: Pdf Table
1. Under the Chemistry tab, do the following settings:
(a) Ensure that Equilibrium and Adiabatic options are selected.
(b) Set the Rich Flammability Limit to 1.
2. Under the Boundary tab, do the following settings:
(a) Specify the value ofTemperature for Fuel and Oxid as 300 K and 650 K respec-tively.
(b) Set the Species Units as Mass Fraction.
(c) Set the composition of Fuel and Oxid for the Species as shown in the followingtable:
Species Fuel Oxid
ch4 0.0453 0
n2 0.7283 0.767
o2 0.2264 0.233
3. Under the Table tab, set retain the default settings and click Calculate PDF Table.
4. Under Premixed tab, examine the properties of unburnt mixture and laminar flamespeed.
5. Examine the relationship between Mean Temperature and Mean Mixture Fraction.
Display PDF Tables/Curves...
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
6. Write the pdf file, par-premixed.pdf.gz.
File Write PDF...
Step 4: Materials
FLUENT will automatically select pdf-mixture under Mixture Materials, and the mixturespecies as defined in the pdf. The Density will be set as pdf and the Laminar Flame Speedas prepdf-polynomial.
1. Retain the default values for the other parameters.
Step 5: Operating Conditions
1. Retain the default operating conditions.
Step 6: Boundary Conditions
1. Set the boundary conditions for air inlet.
(a) Specify the Velocity Specification Method as Components and set the Axial-Velocityto 10.
(b) Specify the Turbulence Specification Method as Intensity and Hydraulic Diameterand set Hydraulic Diameter to 0.0254.
(c) Retain the default values for the other parameters.
Note: The Progress Variable (c) = 0 specifies reactant mixture, but since youhave specified the Mean Mixture Fraction (f) as 0, this will be treated as a
non-combustible mixture. In fact, you can use either values of c; 0 or 1, andthe air inlet results should not vary.
2. Set the boundary conditions for air-fuel inlet.
(a) Set the Axial-Velocity to 50 m/s and Swirl-Velocity to 30 m/s.
(b) Set the Hydraulic Diameter and Mean Mixture Fraction to 0.0254 and 1 respec-tively.
(c) Retain the default values for the other parameters.
3. Set the boundary conditions for the outlet zone.
(a) Set the Backflow Hydraulic Diameter and Backflow Progress Variable to 0.13 and1 respectively.
(b) Retain the default values for the other parameters.
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
Step 7: First Order Solution
1. Solve for Flow, Swirl Velocity, and Turbulence equations.
(a) Keep the default values for Under-Relaxation Factors and Discretization scheme.
(b) Enable the plotting of residuals during calculation.
(c) Initialize the flow field and compute from all zones. Save the case file par-premixed.cas.g
(d) Start the calculation by requesting 1000 iterations.
(e) Save the data file par-premixed.dat.gz
Scaled ResidualsFLUENT 6.2 (axi, swirl, segregated, ske)
Oct 26, 2005
Iterations
2252001751501251007550250
1e+00
1e-01
1e-02
1e-03
1e-04
epsilonkswirly-velocityx-velocitycontinuityResiduals
Figure 3: Scaled Residuals
(f) Define a region with the following values:
Adapt Region...
Input Coordinates Value
Xminimum (m) 0.10
Xmaximum (m) 0.14
Yminimum (m) 0
Ymaximum (m) 0.03
(g) Patch a region close to fuel-air inlet.
i. Under Registers To Patch, select the marked region hexahedron-r0.
ii. Select Progress Variable under Variable.
iii. Retain the default Value of 0 and click Patch.
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
2. Solve for all the equations.
(a) Request for an additional 500 iterations.
(b) Save the case and data files, par-premixed-1st.cas.gz.
Scaled ResidualsFLUENT 6.2 (axi, swirl, segregated, pdf14, ske)
Oct 26, 2005
Iterations
6005004003002001000
1e+00
1e-01
1e-02
1e-03
1e-04
1e-05
1e-06
fvarfmeanepsilonkpremixcswirly-velocityx-velocitycontinuityResiduals
Figure 4: Scaled Residuals
Step 8: Second Order Solution
1. Change the discretization for the following parameters.
Parameter Value
Pressure Second Order
Momentum Second Order Upwind
Swirl Velocity Second Order Upwind
Turbulence Kinetic Energy Second Order Upwind
Turbulence Dissipation Rate Second Order Upwind
Progress Variable Second Order Upwind
Mean Mixture Fraction Second Order Upwind
Mixture Fraction Variance Second Order Upwind
2. Request for an additional 500 iterations.
3. Save the case and data file, par-premixed-2nd.cas.gz.
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
Scaled ResidualsFLUENT 6.2 (axi, swirl, segregated, pdf14, ske)
Oct 26, 2005
Iterations
7006005004003002001000
1e+00
1e-01
1e-02
1e-03
1e-04
1e-05
1e-06
fvarfmeanepsilonkpremixcswirly-velocityx-velocitycontinuityResiduals
Figure 5: Scaled Residuals
Step 9: Postprocessing
Plot vectors and contours for various parameters as described below:
1. Display Velocity Vectors (Figure 6).
Set the Scale Factor to 10 and Skip Value to 3.
2. Display Contours of Stream Function (Figure 7).
Select Velocity... and Stream Function under Contours Of.
3. Display filled Contours of mean Progress Variable (Figure 8).
Select Premixed Combustion... and Progress Variable under Contours Of.
4. Display filled Contours of Static Temperature (Figure 9).
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
Velocity Vectors Colored By Velocity Magnitude (m/s)FLUENT 6.2 (axi, swirl, segregated, ske)
Oct 26, 2005
5.85e+015.57e+01
5.28e+01
4.99e+01
4.70e+01
4.41e+01
4.12e+01
3.83e+01
3.54e+01
3.25e+01
2.96e+01
2.67e+01
2.38e+01
2.09e+01
1.80e+01
1.51e+01
1.22e+01
9.34e+00
6.45e+00
3.55e+00
6.59e-01
Figure 6: Velocity Vectors
Contours of Stream Function (kg/s)FLUENT 6.2 (axi, swirl, segregated, ske)
Oct 26, 2005
2.69e-02
2.55e-02
2.42e-02
2.29e-022.15e-02
2.02e-02
1.88e-02
1.75e-02
1.61e-02
1.48e-02
1.34e-02
1.21e-02
1.08e-02
9.41e-03
8.07e-03
6.72e-03
5.38e-03
4.03e-03
2.69e-03
1.34e-03
0.00e+00
Figure 7: Contours of Stream Function
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
Contours of Progress Variable Oct 26, 2005FLUENT 6.2 (axi, swirl, segregated, ske)
1.00e+00
0.00e+00
5.00e-02
1.00e-01
1.50e-01
2.00e-01
2.50e-01
3.00e-01
3.50e-01
4.00e-01
4.50e-01
5.00e-01
5.50e-01
6.00e-01
6.50e-01
7.00e-01
7.50e-01
8.00e-01
8.50e-01
9.00e-01
9.50e-01
Figure 8: Contours of Progress Variable
Contours of Static Temperature (k) Oct 26, 2005FLUENT 6.2 (axi, swirl, segregated, ske)
1.91e+03
3.00e+02
3.81e+02
4.61e+02
5.42e+02
6.22e+02
7.03e+02
7.83e+02
8.64e+02
9.44e+02
1.02e+03
1.11e+03
1.19e+03
1.27e+03
1.35e+03
1.43e+03
1.51e+03
1.59e+031.67e+03
1.75e+03
1.83e+03
Figure 9: Contours of Static Temperature
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
5. Display contours of species mass fractions.
(a) Mass fraction ofCH4 (Figure 10).
Select Species... and Mass Fractions of ch4 under Contours Of.
(b) Mass fraction ofH2
O (Figure 11).(c) Mass fraction ofCO2 (Figure 12).
(d) Mass fraction ofCO (Figure 13).
(e) Mass fraction ofN2 (Figure 14).
Contours of Mass fraction of ch4 Oct 26, 2005FLUENT 6.2 (axi, swirl, segregated, ske)
4.53e-02
0.00e+00
2.27e-03
4.53e-03
6.79e-03
9.06e-03
1.13e-02
1.36e-02
1.59e-02
1.81e-02
2.04e-02
2.26e-02
2.49e-02
2.72e-02
2.94e-02
3.17e-02
3.40e-02
3.62e-02
3.85e-02
4.08e-02
4.30e-02
Figure 10: Mass Fraction ofCH4
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
Contours of Mass fraction of h2o Oct 26, 2005FLUENT 6.2 (axi, swirl, segregated, ske)
9.09e-02
0.00e+00
4.55e-03
9.09e-03
1.36e-02
1.82e-02
2.27e-02
2.73e-02
3.18e-02
3.64e-02
4.09e-02
4.55e-02
5.00e-02
5.46e-02
5.91e-02
6.37e-02
6.82e-02
7.28e-02
7.73e-028.18e-02
8.64e-02
Figure 11: Mass Fraction ofH2O
Contours of Mass fraction of co2 Oct 26, 2005FLUENT 6.2 (axi, swirl, segregated, ske)
1.11e-01
0.00e+00
5.56e-03
1.11e-02
1.67e-02
2.23e-02
2.78e-02
3.34e-02
3.90e-02
4.45e-02
5.01e-02
5.56e-02
6.12e-02
6.68e-02
7.23e-02
7.79e-02
8.35e-02
8.90e-02
9.46e-02
1.00e-01
1.06e-01
Figure 12: Mass Fraction ofCO2
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
Contours of Mass fraction of co Oct 26, 2005FLUENT 6.2 (axi, swirl, segregated, ske)
2.06e-04
0.00e+00
1.03e-05
2.06e-05
3.10e-05
4.13e-05
5.16e-05
6.19e-05
7.23e-05
8.26e-05
9.29e-05
1.03e-04
1.14e-04
1.24e-04
1.34e-04
1.45e-04
1.55e-04
1.65e-04
1.76e-041.86e-04
1.96e-04
Figure 13: Mass Fraction ofCO
Contours of Mass fraction of n2 Oct 26, 2005FLUENT 6.2 (axi, swirl, segregated, ske)
7.67e-01
7.28e-01
7.30e-01
7.32e-01
7.34e-01
7.36e-01
7.38e-01
7.40e-01
7.42e-01
7.44e-01
7.46e-01
7.48e-01
7.50e-01
7.52e-01
7.53e-01
7.55e-01
7.57e-01
7.59e-01
7.61e-01
7.63e-01
7.65e-01
Figure 14: Mass Fraction ofN2
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Tutorial: Partially Premixed Combustion in a Co-axial Combustor
Results
The partially premixed model in FLUENT can be used to simulate a combustion system,where the combustion process is neither purely premixed nor purely non-premixed. Bothpremixed and non-premixed properties can be investigated using the postprocessing results
as shown above.
Summary
Application of the partially premixed model, based on both non-premixed (mixture-fractionbased) and premixed (mean progress variable based) models has been demonstrated.
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