A new turbulence model for offshore wind turbine standards

Abstract

Correct turbulence intensity modeling is crucial for fatigue load estimation for wind turbine structural design. It is well known that the International Electrotechnical Commission 61400-3 Normal Turbulence Model recommended for offshore wind turbine design is not representative of offshore wind conditions. A new model is urgently needed as offshore wind energy is rapidly developing worldwide. After evaluating the suitability of the Normal Turbulence Model at three sites in Asia, Europe and the USA, it is found that wind-wave interaction and stability correction should be taken into account in modeling the offshore turbulence intensity and wind speed relationship. Therefore, a new turbulence intensity model, which models wind-wave interaction with the Charnock equation and adjusts for the influence of atmospheric stability through empirical turbulence scaling functions for the unstable atmospheric boundary layer, was developed. The new model is physically based and is tested against observations from the three sites. It shows better performance than the Normal Turbulence Model and hence is recommended to replace the Normal Turbulence Model. For model application, only two parameters are required, which are defined herein to represent offshore sites with high, medium and low turbulence intensities.

Simplified critical mudline bending moment spectra of offshore wind turbine support structures

“…It is to be noted that offshore turbulence intensities are lower than those onshore; however, at high wind speeds, it remains steady, and even an increase in turbulence is seen at very high wind speeds (>25 m s −1 ). This was also observed in the measurements of Wang et al . and Türk and Emeis, for example.…”

Assessment of IEC Normal Turbulence Model and Modelling of the Wind Turbulence Intensity for Small Wind Turbine Design in Tropical Area: Case of the Coastal Region of Benin

“…However is not linear as specified in the IEC model standard. This result is in line with the studies of Ren et al (2018) and Wang et al (2013). It is also obvious that σ evolves more rapidly with wind speeds greater than 12 m/s and slowly with wind speeds below 8 m/s.…”

“…Leu et al (2014) studied the performance of the model in Taiwan and also determined the appropriate parameters of this model for this study area as a reference for future wind farms. Wang et al (2013) after having evaluated the IEC61400-3 normal turbulence model at three sites in Asia, Europe and the United States, the authors developed a new model. It is taking into account the wind-wave interaction with the Charnock equation adjusted by empirical functions of turbulence scale for the unstable atmosphere.…”

Using Large-Eddy Simulations to Define Spectral and Coherence Characteristics of the Hurricane Boundary Layer for Wind-Energy Applications

“…Such simulations rely on theoretical spectral (e.g., Kaimal et al (1972) and von Kármán and Lin (1951)) and coherence (e.g., IEC exponential coherence (IEC 2007)) models that may not necessarily represent the true inflow 1 conditions, particularly in a hurricane. Although the IEC 61400-3 (International Electrotechnical Commission Design Requirements for Offshore Wind Turbines) standard states that turbulence models defined for onshore turbine design should also be used for offshore turbine design, Wang et al (2014) found that the turbulence intensity model referred to as the Normal Turbulence Model (IEC 2007), recommended in the IEC 61400-3, does not represent the non-linear relationship between offshore turbulence intensity and wind speed.…”