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Using Mesoscale Weather Model Output 

as Boundary Conditions for Atmospheric 

Large-Eddy Simulations and Wind-Plant 

Aerodynamics Simulations

International Conference on Future Technologies 

for Wind Energy

University of Wyoming

October 7‒9, 2013

Matthew J. Churchfield

John Michalakes

Brian Vanderwende

Sang Lee

NREL/PR-5000-61122

Michael A. Sprague

Julie K. Lundquist

Avi Purkayastha

Patrick J. Moriarty
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Subject and Motivation

• The Subject: Mesoscale-microscale one-way 

coupled simulation of atmospheric flow with focus 

on turbulence evolution

• The Motivation: Real wind plants are subject to 

microscale weather that is driven by mesoscale 

weather. Canonical microscale simulations do not 

capture:

o Frontal passages

o Large-scale mean wind direction/speed changes

o Significant wind direction/speed variation across the plant
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Simulation Tools

• Mesoscale – WRF 

o Nested Weather Research and Forecasting (WRF) model

o Compressible, structured, higher-order finite-difference spatial scheme

• Intermediary – WRF-LES

o Large-eddy simulation (LES) mode WRF (WRF-LES)

o 1.5 equation turbulent-kinetic-energy (TKE) subgrid-scale (SGS) model

• Microscale – OpenFOAM

o Created from Open-source Field Operations and Manipulations (OpenFOAM) computational 

fluid dynamics toolbox

o Incompressible atmospheric LES solver with buoyancy forcing and shear stress lower 

boundaries

o Unstructured, second-order finite-volume solver

o Standard Smagorinksy model, Cs=0.135 (dynamic models available)

• Turbine Model – FAST

o NREL’s Fatigue, Aerodynamics, Structures, and Turbulence (FAST) tool

o Blade element actuator line rotor with turbine system dynamics and control response model
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Simulation Tools

NREL’s Multiscale Coupling Effort:

Available at http://wind.nrel.gov/designcodes/simulators/sowfa/

Mesoscale weather modeling

(WRF)

Microscale/wind-plant-scale large-eddy 

simulation (LES) (OpenFOAM)

Turbine system/structural 

dynamics (FAST)

Photo by Dennis Schroeder, 

NREL 19075

Photo by Iberdrola Renewables, Inc., NREL 15177

Photo by NASA, NREL 03565

The Simulator for On/Offshore Wind Farm Applications (SOWFA)
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Mesoscale-Microscale Simulation Strategy

1 km

flow

inner-nest 

WRF-LES

Neumann: U, T, p

Dirichlet: U, T from WRF

Neumann: p

Dirichlet: surface T flux from WRF

Neumann: p

Surface stress model

1. Run WRF and WRF-LES 

2. Interpolate time history to OpenFOAM 

boundary locations and initial field to 

OpenFOAM interior

3. Run OpenFOAM using WRF-LES 

initialization and boundary conditions
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Case Simulated

• Crop and Wind Energy eXperiment (CWEX)

• Wind plant in Iowa over relatively flat farm land

• Summer, daytime case – moderately convective

• 1 hr of coupled simulation

Image by Brian Vanderwende photo courtesy of Julie Lundquist
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Results: Coupling with No Turbines

WRF-LES

OpenFOAM

horizontal

horizontal

vertical

vertical

from WRF-LES 

domain

from OpenFOAM

domain

Instantaneous velocity at 85 m above surface
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Results: Coupling with No Turbines

WRF-LES 

initialized flow 

field

Finer-scale 

flow features 

begin to 

develop 

Region in 

which finer 

scales visually 

appear fully 

developed

Black crosses 

denote actual 

turbine 

locations 

(turbines not 

included in this 

simulation)

Horizontal velocity time history at 80 m above surface from OpenFOAM microscale calculation
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Results: Coupling with No Turbine

Spectra evolution in time

Spectrum of different segments of time history averaged over y constant line

Higher frequency 

energy substantially 

builds, then slightly 

decreases
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Results: Coupling with No Turbines

Spectra evolution in space

Spectrum of segments of time history averaged over time and y-constant lines

Higher frequency 

energy substantially 

builds, then slightly 

decreases
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Results: Coupling with No Turbines

Spectra evolution in space

Time-averaged integral of high wavenumber part of spectrum at every location

• Roughly 1.5 km required for high wave number energy to “fill in”

• High wave number content “overshoots” then decays

horizontal vertical

 κ1 κ2
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Results: Coupling with No Turbines

• Near the surface, the 

horizontal velocity predicted 

in OpenFOAM domain rapidly 

decreases with distance from 

the inflow boundaries

• Unclear why this mismatch 

between WRF-LES and 

OpenFOAM LES occurs
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Coupling with Turbines

• Eight 1.5-MW turbines 

modeled using rotating 

actuator lines

• Turbine model includes 

control so rotor speed 

reacts to flow 

• Multi-resolution 

unstructured mesh

o 10 m background

o 1.25 m around turbine and 

in wake

10m

1.25 m

+ + + + + +

+

+

Horizontal slice through 

microscale mesh with region 

of refinement around turbines 

and wakes
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Results: Coupling with Turbines

Blade out-of plane bending load
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Conclusions

• One-way mesoscale-microscale coupling allows for non-canonical 

conditions

o Extreme events

o Nonhomogeneous flow across farm

o Ramp events

• Extension to two-way coupling will facilitate wind plant parameterization 

for mesoscale models

o Plant-to-plant interaction

o Environmental effects

• Significant distance necessary for microscale high wavenumber content 

to develop (1.5 km in this case)

• Some time also required for high wavenumber development

• Following the flow direction or progressing in time, an overshoot in high 

wavenumber energy is observed, followed by decay
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Future Work

• Examine effect of mesoscale inner nest resolution

o Does coarser resolution require more distance in microscale 

domain for high wave number turbulence development?

• Examine effect of atmospheric stability

o Do neutral conditions require more distance in microscale 

domain for high wave number turbulence development?

• Examine inflow perturbation methods 

o i.e., Muñoz-Esparza and Kosović

• Would a dynamic SGS model avoid overshoot of high 

wavenumber energy content?
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Questions

Matt Churchfield

Matt.Churchfield@nrel.gov

303-384-7080