14.4.6. Solution

a.The warped-face gradient correction is designed to improve gradient accuracy for all gradient methods.

b.The relaxation of high order terms will help to improve the solution behavior of flow simulations when higher order spatial discretizations are used (higher than first).

2.Ensure that the plotting of residuals is enabled during the calculation.

Solution → Reports → Residuals...

3.Create a surface report definition of mass-weighted average of co2 at the outlet.

Solution → Reports → Definitions → New → Surface Report → Mass-Weighted Average...

4.Initialize the solution.

Solution → Initialization → Initialize

5.Save the case file (combustor_edm.cas.gz).

File → Write → Case...

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6.Start calculation.

Solution → Run Calculation → Advanced...

a.Set the global Timescale Factor to 5.

The Timescale Factor allows you to further manipulate the computed Time Step calculated by ANSYS Fluent. Larger time steps can lead to faster convergence. However, if the time step is too large it can lead to solution instability.

b.Enter 500 for Number of Iterations.

c.Click Calculate.

All scaled residuals have met the criteria for a converged solution (Figure 14.3: Scaled Residuals (p. 488)), and the relative amount of CO2 exiting the combustor outlet has become stable (Figure 14.4: Convergence History of Mass-Weighted Average CO2 on the Outlet (p. 489)).

Figure 14.3: Scaled Residuals

Figure 14.4: Convergence History of Mass-Weighted Average CO2 on the Outlet

7. Save the case and data files (combustor_edm.cas.gz and combustor_edm.dat.gz).

File → Write → Case & Data...

14.4.7. Postprocessing for the Eddy-Dissipation Solution

1.Check the mass flux balance.

Postprocessing → Reports → Fluxes...

Warning

Although the mass flow rate history indicates that the solution is converged, you should also check the net mass fluxes through the domain to ensure that mass is being conserved.

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a.Select fuelinlet, inletair1, inletair2 and outlet from the Boundaries selection list.

b.Retain the default Mass Flow Rate option.

c.Click Compute and close the Flux Reports dialog box.

Warning

The net mass imbalance should be a small fraction (for example, 0.5%) of the total flux through the system. If a significant imbalance occurs, you should decrease the residual tolerances by at least an order of magnitude and continue iterating.

2.Report the total sensible heat flux.

Results → Reports → Fluxes...

a.Select Total Sensible Heat Transfer Rate in the Options list.

b.Select all the boundaries from the Boundaries selection list (you can click the select-all button ().

c.Click Compute and close the Flux Reports dialog box.

Note

The energy balance is good because the net result is small compared to the heat of reaction.

3.Create an XZ plane, which will be used for plotting the results.

Results → Surface → Create → Plane...

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a.Enter plane_xz in for New Surface Name.

b.In the Options group box, select Point and Normal.

c.In the Points group box, enter 1, 0, 1 for x0, y0, z0, respectively.

d.In the Normal group box, enter 0, 1, 0 for x0, y0, z0, respectively.

e.Click Create and close the Plane Surface dialog box.

4.Display filled contours of CO2 mass fraction in the combustion chamber (Figure 14.5: Contours of CO2 Mass Fraction (p. 493)).

Results → Graphics → Contours → New...

a.Enter co2-mass-fraction for Contour Name.

b.Enable Filled in the Options group box.

c.From the Contours of drop-down lists, select Species... and Mass Fraction of co2.

d.From the Surfaces selection list, deselect all surfaces and select plane_xz.

e.In the Coloring group box, select Smooth.

f.Click Save/Display and rotate the view as shown in Figure 14.5: Contours of CO2 Mass Fraction (p. 493).

Figure 14.5: Contours of CO2 Mass Fraction

Note

You may need to deselectHeadlight and then Lighting in the View ribbon tab (Display group).

The contour map of the CO2 concentration shows that the flow is mixing and reacting properly in the combustor.

5.Display filled contours of oxygen mass fraction on the surface plane_xz (Figure 14.6: Contours of O2 Mass Fraction (p. 494)).

Results → Graphics → Contours → New...

a.Enter o2-mass-fraction for Contour Name.

b.Enable Filled in the Options group box.

c.From the Contours of drop-down lists, select Species... and Mass Fraction of o2.

d.From the Surfaces selection list, deselect all surfaces and select plane_xz.

e.In the Coloring group box, select Smooth.

f.Click Save/Display.

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Figure 14.6: Contours of O2 Mass Fraction

6.Display filled contours of temperature on the aluminum combustor walls (Figure 14.7: Contours of Static Temperature on the Combustor Walls (p. 495)).

Results → Graphics → Contours → New...

a.Enter surface-temperature for Contour Name.

b.Enable Filled in the Options group box.

c.From the Contours of drop-down lists, select Temperature... and Static Temperature.

d.From the Surfaces selection list, deselect all surfaces and select wall-part-fluid and wallvanes.

e.In the Coloring group box, select Smooth.

f.Click Save/Display.