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Setup and Solution

g.Enable Write to File in the Options group box to save the wall y+ profile.

h.Click the Write... button to open the Select File dialog box.

i. Enter ke-yplus.xy in the XY File text entry box and click OK.

Note

Ideally, while using enhanced wall treatment, the wall y+ should be in the order of 1 (at least less than 5) to resolve the viscous sublayer. The plot justifies the applicability of enhanced wall treatment to the given mesh.

i.Close the Solution XY Plot dialog box.

9.4.10. Solution Using the RNG k- ε Model

Recalculate the solution using the RNG - turbulence model.

1.Enable the RNG - turbulence model with the enhanced near-wall treatment.

Physics → Models → Viscous...

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a.Select RNG in the k-epsilon Model list.

b.Enable Differential Viscosity Model and Swirl Dominated Flow in the RNG Options group box.

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Setup and Solution

The differential viscosity model and swirl modification can provide better accuracy for swirling flows such as the disk cavity.

For more information, see RNG swirl modification in the Fluent Theory Guide.

c.Retain Enhanced Wall Treatment as the Near-Wall Treatment.

d.Click OK to close the Viscous Model dialog box.

2.Continue the calculation by requesting 300 iterations.

Solution → Run Calculation

3.Save the case and data files (disk-rng.cas.gz and disk-rng.dat.gz).

File → Write → Case & Data...

9.4.11. Postprocessing for the RNG k- ε Solution

1.Plot the radial velocity distribution for the RNG - solution and compare it with the distribution for the standard - solution.

Results → Plots → XY Plot → Edit...

a.Enter 1 and 0 for X and Y respectively in the Plot Direction group box.

b.Select Velocity... and Radial Velocity from the Y Axis Function drop-down lists.

c.Select aaa_y=37cm and deselect wall-6 from the Surfaces selection list.

d.Disable the Write to File option.

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e.Click the Load File... button to load the - data.

i.Select the file ke-data.xy in the Select File dialog box.

ii.Click OK.

f.Click the Axes... button to open the Axes - Solution XY Plot dialog box.

i.Enable Auto Range in the Options group box.

ii.Click Apply and close the Axes - Solution XY Plot dialog box.

g.Click the Curves... button to open the Curves - Solution XY Plot dialog box, where you will define a different curve symbol for the RNG - data.

i.Retain 0 for the Curve #.

ii.Select x from the Symbol drop-down list.

iii.Click Apply and close the Curves - Solution XY Plot dialog box.

h.Click Plot in the Solution XY Plot dialog box (Figure 9.8: Radial Velocity Distribution — RNG k- ε and Standard k- ε Solutions (p. 349)).

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Setup and Solution

Figure 9.8: Radial Velocity Distribution — RNG k- ε and Standard k- ε Solutions

The peak velocity predicted by the RNG - solution is higher than that predicted by the standard - solution. This is due to the less diffusive character of the RNG - model. Adjust the range of the axis to magnify the region of the peaks.

i.Click the Axes... button to open the Axes - Solution XY Plot dialog box, where you will specify the -axis range.

i.Disable Auto Range in the Options group box.

ii.Retain the value of 0 for Minimum and enter 1 for Maximum in the Range dialog box.

iii.Click Apply and close the Axes - Solution XY Plot dialog box.

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j.Click Plot.

The difference between the peak values calculated by the two models is now more apparent.

Figure 9.9: RNG k- ε and Standard k- ε Solutions (x=0 cm to x=1 cm)

2.Plot the wall y+ distribution on the rotating disk wall along the radial direction Figure 9.10: wall-6 — RNG k- ε and Standard k- ε Solutions (x=0 cm to x=43 cm) (p. 352).

Results → Plots → XY Plot → Edit...

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Setup and Solution

a.Select Turbulence... and Wall Yplus from the Y Axis Function drop-down lists.

b.Deselect aaa_y=37cm and select wall-6 from the Surfaces selection list.

c.Enter 0 and 1 for X and Y respectively in the Plot Direction group box.

d.Select any existing files that appear in the File Data selection list and click the Free Data button to remove the file.

e.Click the Load File... button to load the RNG - data.

i.Select the file ke-yplus.xy in the Select File dialog box.

ii.Click OK.

f.Click the Axes... button to open the Axes - Solution XY Plot dialog box.

i.Retain the default selection of X from the Axis group box.

ii.Retain the default value of 0 for Minimum and enter 43 for Maximum in the Range group box.

iii.Click Apply and close the Axes - Solution XY Plot dialog box.

g.Click Plot in the Solution XY Plot dialog box.

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