Handing Turbulence in Multiphase Flow

[hgopalan]

The ABL setup for multiphase flow is setup to run under laminar model and this needs to be modified in the future. There are three components which needs to be consistently setup to avoid oscillation and unrealistic values of turbulent viscosity at the air-water interface.

1. Initial velocity profile in air and water: This can generate initial gradients vertically and with the density ratio, can cause the turbulent viscosity to grow.
2. Density difference: The difference in density between air and water causes unrealistic turbulent viscosity growth at interface and can also result in thermal oscillations in the water layer.
3. Wave energy production: The movement of waves can generate velocity gradients, which are a solid body type production term and should not generate turbulent viscosity. This is more complicated for a linear model and may require non-linear models to handle.

I tried to address issues 2. and partially 3. using a modification to the Smagorinsky model. We replace

Shear Production = Dissipation

by Shear Production + Density Gradient Production = Dissipation and recompute the turbulent viscosity. Initial results are shown below for the abl_multiphase_laminar flow case with Smagorinsky model replacing laminar model. The modification is still in the testing phase and I am hoping to have more ideas and discussion for implementation.

Wind Speed

Turbulent Viscosity

Turbulence has been currently turned off in the water since the initial shear between air and water profile generates vertical winds which causes oscillations in the temperature in the water region.

[mbkuhn]

linking #987 because that was an early attempt