NREL 5MW Rotor in Atmospheric Boundary Layer With OpenFAST/BeamDyn Fluid Structure Interaction

This benchmark contains a geometry and boundary-layer resolved model of the NREL 5MW reference turbine [1] in a developed near-neutral convective atmospheric boundary layer with a mean hub-height streamwise velocity of 11.4m/s.

  • Hub-height: 90m

  • Blade Radius: 63m

  • Rated Power: 5 MW

  • Type: Upwind 3 Blade

  • Simulation dt: 0.003443526170799 s

  • OpenFAST dt: 0.0008608815426997245 s

Note on run-time: Current results are for approximately 180s simulation time, but a minimum of 300s will be posted as results become available.

Note on turbine controller: This case will be re-run in Q3 as a result of a small bug in the controller. If interested in running this benchmark, please contact the authors for up-to-date scheduling

Simulation Setup

Freestream Conditions

A near-neutral convective boundary layer precursor was run to feed the domain for this case. Full details are posted here: Convective ABL for NREL5MW

10 minute flow statistics:

  • Hub-height streamwise velocity: 11.4 m/s

  • Hub-height flow direction: ~240.0 degrees

avgmetmest60

CFD Mesh

meshpicture

Total number of cells: 155,363,046

The near-body (Nalu-Wind) mesh was created using a proprietary surface mesher, pyHyp, and Pointwise. Three blades are split at the hub, and an unconnected tower is included.

  • Hexahedral cells

  • Cell count: 13,436,646

Off-body (AMR-Wind) mesh was generated using the built-in capability of AMR-Wind. Off-body mesh information is summarized below

  • Mesh topology: structured hex with nested refinements

  • Domain in x= 0 to 5000m, y=0m to 5000m, z=0m to 1000m

  • Initial grid size: 10m

  • Finest cell size: 0.625m with 4 AMR levels

  • Cell count: 141,926,400

Results

Timeseries results from OpenFAST

The plots below show timeseries of some key quantities as reported by OpenFAST (which in this simulation is acting as the structural and controller model).

openfastresults

Mean values over time period: 60s to 180s

variable

value

Generator Power

4165.49 kW

Rotor Aero Torque

3509.12 kN-m

Rotor Speed

12.0 rpm

Rotor Thrust

643.58 kN

B1 Root Flap Moment (x)

8.300869e+05 N-m

B1 Root Edge Moment (y)

7.869930e+06 N-m

B1 Tip Deflection x-direction

4.24 m

B1 Pitch

2.07 degrees

Simulation Timings

This benchmark was run at Sandia National Laboratories on a machine comprised of 112 Intel® Xeon® Platinum 8480+ CPU cores per node.

Processor Decomposition:

  • Nalu-Wind: 672 ranks

  • AMR-Wind: 4928 ranks

Timings:

  • Mean wall-clock time per timestep for entire simulation: 17.75s

  • Mean wall-clock time per timestep per cell 1.142e-07s

Quick Exawind Simulation Guide

Step 0: Run the ABL precursor in AMR-Wind

This simulation is driven by an ABL precursor, run in AMR-Wind, with recorded boundary planes, initial conditions, and average temperature. (See case linked above)

Step 1: Develop and decompose overset mesh

It is necessary to develop a near-body mesh surrounding the blade surface in Nalu-Wind using external tools. This mesh should be in the Exodus II format and decomposed to approximately 20K cells per core available to Nalu-Wind. (Current mesh provided via dvc/github assets)

Step 2: Run the OpenFAST precursor for 5760 OpenFAST timesteps (approximately 1 rotation)

srun -n 1 openfastcpp inp.yaml

Step 3: Run the full Exawind suite

srun -N 50 -n 5600 exawind --nwind 672 --awind 4928 nrel5mw.yaml &> log

Step 4: Setup and Run the full Exawind suite restart(s)

srun -N 50 -n 5600 exawind --nwind 672 --awind 4928 nrel5mw_r1.yaml &> log_1

References

[1]: Jonkman, J. et al, “Definition of a 5-MW Reference Wind Turbine for Offshore System Development” NREL/TP-500-38060, 2009. https://www.nrel.gov/docs/fy09osti/38060.pdf