The paper “Assessment of Simulation and Modelling Errors for Three CFD Wind Models” presents an independent comparison of three computational fluid dynamics (CFD) simulation tools used to estimate wind resources over complex terrains. The three models compared in the study are:

1. OpenFOAM – A finite-volume solver using Reynolds-Averaged Navier-Stokes (RANS) equations with a k-ε turbulence closure.
2. WindSim – A commercial software also solving the RANS equations with a RNG k-ε turbulence model.
3. ORFEUS – A linearized spectral solver based on Fourier-Chebyshev decomposition with a zero-equation turbulence closure.

Key Highlights:

• Objective: The study aims to evaluate the uncertainty and error levels in wind resource estimation using these three models by comparing their outputs to SCADA (Supervisory Control and Data Acquisition) and mast data.
• Study Sites: Three sites with varying terrain complexity were selected. Two were ridges with medium complexity, and the third was an almost flat terrain with lower complexity.
• Methodology:
  • The simulations were conducted independently by different groups using the same terrain and roughness data.
  • Turbines were deliberately excluded from the simulations to avoid errors related to turbine modeling.
  • SCADA data from existing met masts were used to validate the results.

Findings:

• Simple Terrain: For low-complexity terrain, all three models showed good agreement with SCADA data.
• Complex Terrain: For terrains with mountainous features, larger discrepancies were observed between models. WindSim performed well for some wind directions but struggled in others. The two RANS-based models (OpenFOAM and WindSim) captured higher velocity gradients more effectively than ORFEUS.
• Uncertainty in Site 2: Errors were amplified for one of the sites due to its distance from the reference mast.
• Turbulence Modeling Differences: RANS models using two-equation turbulence closures provided better alignment with real flow data compared to ORFEUS, which struggled in high-velocity gradient regions.

Conclusions:

• Nonlinear CFD models (OpenFOAM, WindSim) better capture flow dynamics over complex terrain than the linearized ORFEUS model.
• ORFEUS can be a viable option for simple terrain but has limitations in capturing wind speed variations in complex terrains.
• Model uncertainty increases with terrain complexity, emphasizing the importance of accurate turbulence modeling and site-specific validation.

The study underscores the need for further research to improve wind simulation accuracy, particularly in complex terrains, to enhance wind resource assessment for wind farm planning​.

Link: https://www.academia.edu/36902350/Assessment_of_simulation_and_modelling_errors_for_three_CFD_wind_models