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Droplet Impingement on the NACA0012

17.Go to the ribbon bar of your Fluent Icing window and, under View → Quick-view → Contour, choose Heat flux (walls) to output the convective heat flux over the rough NACA0012. See figure below.

Figure 27.4: Convective Heat Flux over the NACA0012

27.3. Droplet Impingement on the NACA0012

The objectives of this tutorial are to compute the droplet concentration around the NACA0012 airfoil and to compare the collection efficiency of a monodispersed droplet simulation to a statistically-distrib- uted droplet diameter solution. Completion of Flow Solution on the Rough NACA0012 Airfoil (p. 892) is required before continuing.

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In a monodispersed droplet calculation, a single droplet diameter represents the icing cloud the aircraft is flying in. In reality, icing clouds never contain only one size of droplets; there is always a distribution of droplet sizes in a cloud. When running a single droplet diameter, the median volumetric diameter (MVD) of the droplets in the cloud is chosen as the monodispersed value. If a more accurate droplet solution is needed, then a distribution of droplet sizes can be solved for, where the MVD of this distribution matches that of the cloud.

You are invited to read sections Set-up → Droplets and Set-up → Boundary Conditions → Inlet Types under Fluent Icing within the Fluent User's Guide for more information on how to set up the input parameters of droplets and/or crystals.

27.3.1. Monodispersed Calculation

In this section, you will learn how to set-up and launch a monodispersed droplet simulation using Fluent Icing.

1.Launch Fluent Icing from your working directory, FLUENT_ICING_NACA0012.

2.Go to File → Preferences…. Select Icing on the left hand-side of the Preferences window. Assign a number of CPUs, 2 to 4 CPUs, next to Default Fluent CPU and set Default work folder to the location of your working directory.

3.Go to File → Open case…. Browse to and select the file naca0012_rough.cas, created in Flow Solution on the Rough NACA0012 Airfoil (p. 892).

4.A message window will ask you to launch Fluent, click Yes. A new simulation tree appears under naca0012_rough.cas(loaded) in the Outline View window.

Note

Alternatively, if you did not close your Fluent Icing window of Flow Solution on the Rough NACA0012 Airfoil (p. 892), you can follow the next steps to set-up this tutorial inside the Simulation naca0012_clean.cas(loaded) of Flow Solution on the Rough NACA0012 Air-

foil (p. 892).

5.Select Set-up under naca0012_rough.cas(loaded). In its Properties window, make sure that Airflow and

Particles are checked, and uncheck Ice.

Note

Set-up, Solve and Results settings of the airflow around the NACA0012 have been carried from Flow Solution on the Rough NACA0012 Airfoil (p. 892). Therefore, they do not need to be updated.

6.Under Set-up → Particles, activate Droplets in Type. Leave the other options unchecked.

7.Go to Droplets, inside Set-up → Particles. In the Properties window of Droplets,

•under Droplet conditions, set the LWC [kg/m3] to 0.00055 and the Droplet diameter [microns] to

20.

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Droplet Impingement on the NACA0012

•under Particles distribution, keep Monodispersed since we will conduct a water catch simulation using a single droplet size.

•under Model, keep Water as the Droplet drag model. This is the default drag law for droplet particles.

8.Under Set-up → Boundary Conditions, go to pressure-far-field and make sure that, under Particles,

Automatic is selected and Droplet custom velocity remains unchecked. The Automatic option will apply the Droplet conditions at the inlet of the pressure-far-field, in this case, the LWC and the MVD. If Droplet custom velocity remains unchecked, the airflow velocity is imposed as the droplet velocity at the inlet. In other words, the relative velocity between air and droplets is considered to be zero at far-field.

Note

When configuring particle flow simulations, boundary conditions are only specified at inlets.

9.Under Solve → Particles, set 300 as the Number of Iterations in Run settings. Keep the default settings in Solver and Initialization.

Note

Inside Initialization, From airflow conditions uses the airflow direction specified in Setup → Airflow as the initial velocity of droplets.

10.Right-click Particles under Solve and choose Initialize to apply the initialization parameters of step 9.

11.Right-click Particles under Solve and choose Calculate to launch the droplet particle simulation in standalone mode.

The calculation stops when the convergence level reaches the convergence limits set on the residual cut-off and on the change in total beta. Otherwise, the simulation continues until it reaches 300 iterations. In the Graphics window, you can look at Momentum, LWC, Average residual curves and the Total Beta and Change in Total Beta convergence curves.

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Figure 27.5: Convergence of Momentum, LWC and Average Residuals

Figure 27.6: Convergence of Total Beta and Change in Total Beta Curves

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Droplet Impingement on the NACA0012

Often the solution in the wake of the droplet flow is still converging while the impingement at the surfaces is fully converged. If you wish to converge the wake and the shadow zones further, the Residual cut-off of the Particles panel under Solve should be reduced. The droplet wake usually is not of interest and it is sufficient to achieve convergence of the total beta alone.

12.When calculations are completed, go to the ribbon bar of your Fluent Icing window and, under View → Quick-view → Contour, choose Collection Efficiency to output the water catch of the monodispersed droplets over the NACA0012. See figure below.

Figure 27.7: Collection Efficiency of Monodispersed Droplets over a NACA0012

13.Repeat these steps to easily output the LWC around the NACA0012. Blue contours define the shadow zone, absence of water droplets. See figure below.

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