Meso-Micro Coupling with no precursor for Terrain

[hgopalan]

The current workflow in AMR - Wind requires a precursor simulation to generate boundary plane for running complex terrain simulations. However, this is not a requirement. This PR proposes an alternative path for running simulations over complex terrain.

1. Based on met-mast measurement, a 1-D vertical wind profile is created along with the required geostrophic wind.
2. The simulation is initialized with the 1-D profile.
3. All the horizontal boundary conditions are replaced with pressure-outflow boundary condition with a sponge layer, forcing the 1-D profile.
4. A forcing zone is added on the upper portion of the domain to drive the wind speed and temperature to be consistent with the 1-D vertical profile.

Future Work:

1. Adding the nudging terms within domain for met-mast or Lidar data
2. Replacing pressure-outflow with WRF-mesoscale boundary plane data and removing the flat terrain restrictions at the boundary.

Please check the type of change introduced:

• Bugfix
• [ X] Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

To Do:

1. Regression test
2. Unit test
3. Documentation

SunZia Wind Farm LES - 150 kms

Flatirons - RANS - 150 kms

[lawrenceccheung]

Hi @hgopalan,

Thanks for documenting the process. One question I have about the MMC coupling with terrain is how we account for the fact that the turbulence will take time to spin-up, and how a time-varying MMC profile can be accounted for. One way to handle it is to include a large, flat inflow region where the turbulence can develop. Depending on the ABL stability state, it might require a shorter/longer region for the turbulence profile to adjust.

Once the 1D MMC profile is time-varying, though, that introduces a time delay between when the velocity/temperature changes and when that turbulence enters the domain. @mchurchf and @ewquon might have some ideas on what to do too.

Lawrence

[hgopalan]

Hi @hgopalan,

Thanks for documenting the process. One question I have about the MMC coupling with terrain is how we account for the fact that the turbulence will take time to spin-up, and how a time-varying MMC profile can be accounted for. One way to handle it is to include a large, flat inflow region where the turbulence can develop. Depending on the ABL stability state, it might require a shorter/longer region for the turbulence profile to adjust.

Once the 1D MMC profile is time-varying, though, that introduces a time delay between when the velocity/temperature changes and when that turbulence enters the domain. @mchurchf and @ewquon might have some ideas on what to do too.

Lawrence

The purpose of this workflow is mainly related to providing a simple method for AEP calculation for the RANS model similar to the method used in commercial RANS tools. The usability of the method and adoption for LES needs some investigation. If a terrain is complex, it does not need a lot of time to spin-up as the heterogeneity generate the flow structures. The terrain is smoothed in the horizontal boundaries and when they encounter a change in elevation it generated the structures for the cases I tested with mountains.

There is no restriction on specifying a time-varying 1-D profile. We just need to move the profile reader to be time-dependent. Will require some code changes but is doable.

There is some difference with the method proposed here. Our aim is to match the met-mast data while providing a reasonable boundary condition which will not cause divergence of the pressure poisson solver. We are not worried about flow spin-up and other issues and expect that the presence of complex terrain will generate the structure.

We may have to tweak the workflow in future if there are discrepancies with measured data. However, this method should be acceptable for RANS.