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Figure 16.5: Pathlines of Air in the Swirling Annular Stream

16.4.8. Creating a Spray Injection

1.Define the discrete phase modeling parameters.

Physics → Models → Discrete Phase...

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Setup and Solution

a.Select Interaction with Continuous Phase in the Interaction group box.

This will include the effects of the discrete phase trajectories on the continuous phase.

b.Retain the value of 10 for DPM Iteration Interval.

c.Select Mean Values in the Contour Plots for DPM Variables group box.

This will make the cell-averaged variables available for postprocessing activities.

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d.Select the Unsteady Particle Tracking option in the Particle Treatment group box.

e.Enter 0.0001 for Particle Time Step Size.

f.Enter 10 for Number of Time Steps.

g.Under the Physical Models tab, select the Temperature Dependent Latent Heat and Breakup (Options group).

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Setup and Solution

h.Under the Numerics tab, select Linearize Source Terms (Source Terms group).

Enabling this option will allow you to run the simulation with more aggressive setting for the Discrete Phase Sources under-relaxation factor to speed up the solution convergence.

i.Click Injections... to open the Injections dialog box.

In this step, you will define the characteristics of the atomizer.

An Information dialog box appears indicating that the Max. Number of Steps has been changed from 50000 to 500. Click OK in the Information dialog box to continue.

j.Click the Create button to create the spray injection.

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k.In the Set Injection Properties dialog box, select air-blast-atomizer from the Injection Type dropdown list.

l.Enter 600 for Number of Streams.

This option controls the number of droplet parcels that are introduced into the domain at every time step.

m.Select Droplet in the Particle Type group box.

n.Select methyl-alcohol-liquid from the Material drop-down list.

o.In the Point Properties tab, specify point properties for particle injections.

i.Retain the default values of 0 and 0 for X-Position and Y-Position.

ii.Enter 0.0015 for Z-Position.

iii.Retain the default values of 0, 0, and 1 for X-Axis, Y-Axis, and Z-Axis, respectively.

iv.Enter 263 K for Temperature.

Scroll down the list to see the remaining point properties.

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Setup and Solution

v.Enter 8.5e-5 kg/s for Flow Rate.

This is the methanol flow rate for a 30-degree section of the atomizer. The actual atomizer flow rate is 12 times this value.

vi.Retain the default Start Time of 0 s and enter 100 s for the Stop Time.

For this problem, the injection should begin at and not stop until long after the time period of interest. A large value for the stop time (for example, 100 s) will ensure that the injection will essentially never stop.

vii.Enter 0.0035 m for the Injector Inner Diameter and 0.0045 m for the Injector Outer Diameter.

viii.Enter 45 degrees for Spray Half Angle.

The spray angle is the angle between the liquid sheet trajectory and the injector centerline.

ix.Enter 82.6 m/s for the Relative Velocity.

The relative velocity is the expected relative velocity between the atomizing air and the liquid sheet.

x.Retain the default Azimuthal Start Angle of 0 degrees and enter 30 degrees for the Azimuthal Stop Angle.

This will restrict the injection to the 30-degree section of the atomizer that is being modeled.

p.In the Physical Models tab, specify the breakup model and drag parameters.

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i.In the Breakup group, ensure that Enable Breakup is selected and TAB is selected from the Breakup Model drop-down list.

ii.Retain the default values of 0 for y0 and 2 for Breakup Parcels.

iii.In the Drag Parameters group box, select dynamic-drag from the Drag Law drop-down list.

The dynamic-drag law is available only when the Breakup model is used.

q.In the Turbulent Dispersion tab, define the turbulent dispersion.

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Setup and Solution

i.Enable Discrete Random Walk Model and Random Eddy Lifetime in the Stochastic Tracking group box.

These models will account for the turbulent dispersion of the droplets.

ii.Click OK to close the Set Injection Properties dialog box.

Note

To modify the existing injection, select its name in the Injections list and click Set..., or simply double-click the injection of interest.

r.Close the Injections dialog box.

Note

In the case that the spray injection would be striking a wall, you should specify the wall boundary conditions for the droplets. Though this tutorial does have wall zones, they are a part of the atomizer apparatus. You need not change the wall boundary conditions any further because these walls are not in the path of the spray droplets.

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s. Click OK to close the Discrete Phase Model dialog box.

2.Specify the droplet material properties.

Setup → Materials → methyl-alcohol-liquid → Create/Edit...

When secondary atomization models (such as Breakup) are used, several droplet properties need to be specified.

a.Ensure droplet-particle is selected in the Material Type drop-down list.

b.Enter 0.00095 kg/m-s for Viscosity in the Properties group box.

c.Ensure that piecewise-linear is selected from the Saturation Vapor Pressure drop-down list.

Scroll down to find the Saturation Vapor Pressure drop-down list.

d.Click the Edit... button next to Saturation Vapor Pressure to open the Piecewise-Linear Profile dialog box.

e.Retain the default values and click OK to close the Piecewise-Linear Profile dialog box.

f.Select convection/diffusion-controlled from the Vaporization Model drop-down list.

g.Click OK to close the Convection/Diffusion Model dialog box.

h.Click Change/Create to accept the change in properties for the methanol droplet material and close the Create/Edit Materials dialog box.

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