| Characteristic Turbulence Intensity | |
For a set of 10-minute time steps, each of which contains a value of turbulence intensity, the characteristic turbulence intensity is equal to the 84th percentile of the turbulence intensity values, meaning the value below which 84% of the values fall. If the turbulence intensity values conform to a normal distribution, the 84% percentile is equal to the mean plus one standard deviation.
Windographer does assume that the turbulence intensity values are normally distributed, so it calculates the characteristic turbulence intensity as the mean plus one standard deviation.
For example, the following table contains 30 time steps of data on mean wind speed, standard deviation of wind speed, and turbulence intensity, which is the ratio of the two:
| Date/Time | Wind Speed (m/s) | Turbulence Intensity | |
|---|---|---|---|
| Mean | Std. Dev. | ||
| 2020-12-22 15:30:00 | 14.5 | 1.2 | 0.0828 |
| 2020-12-22 15:40:00 | 14.2 | 1.3 | 0.0915 |
| 2020-12-22 15:50:00 | 12.6 | 1.2 | 0.0952 |
| 2020-12-22 16:00:00 | 12.3 | 1.0 | 0.0813 |
| 2020-12-22 16:10:00 | 13.3 | 0.8 | 0.0602 |
| 2020-12-22 16:20:00 | 13.0 | 1.0 | 0.0769 |
| 2020-12-22 16:30:00 | 13.4 | 1.0 | 0.0746 |
| 2020-12-22 16:40:00 | 13.7 | 1.0 | 0.0730 |
| 2020-12-22 16:50:00 | 12.8 | 1.0 | 0.0781 |
| 2020-12-22 17:00:00 | 13.7 | 1.0 | 0.0730 |
| 2020-12-22 17:10:00 | 14.2 | 0.9 | 0.0634 |
| 2020-12-22 17:20:00 | 13.9 | 0.7 | 0.0504 |
| 2020-12-22 17:30:00 | 13.8 | 0.9 | 0.0652 |
| 2020-12-22 17:40:00 | 13.6 | 1.1 | 0.0809 |
| 2020-12-22 17:50:00 | 13.1 | 1.0 | 0.0763 |
| 2020-12-22 18:00:00 | 12.2 | 1.1 | 0.0902 |
| 2020-12-22 18:10:00 | 12.5 | 1.0 | 0.0800 |
| 2020-12-22 18:20:00 | 12.4 | 0.8 | 0.0645 |
| 2020-12-22 18:30:00 | 12.7 | 0.8 | 0.0630 |
| 2020-12-22 18:40:00 | 12.3 | 1.1 | 0.0894 |
| 2020-12-22 18:50:00 | 12.1 | 0.7 | 0.0579 |
| 2020-12-22 19:00:00 | 12.7 | 0.7 | 0.0551 |
| 2020-12-22 19:10:00 | 11.4 | 1.0 | 0.0877 |
| 2020-12-22 19:20:00 | 12.1 | 1.0 | 0.0826 |
| 2020-12-22 19:30:00 | 11.6 | 0.8 | 0.0690 |
| 2020-12-22 19:40:00 | 11.4 | 0.9 | 0.0789 |
| 2020-12-22 19:50:00 | 10.7 | 0.7 | 0.0654 |
| 2020-12-22 20:00:00 | 11.0 | 0.8 | 0.0727 |
| 2020-12-22 20:10:00 | 10.8 | 0.8 | 0.0741 |
| 2020-12-22 20:20:00 | 11.7 | 0.7 | 0.0598 |
Those 30 turbulence intensity values (highlighted in the table) have a mean of 0.0738 and a standard deviation of 0.0113. Windographer would therefore calculate the characteristic turbulence intensity over that period as 0.0738 + 0.0113 = 0.0851.
The 2nd edition of IEC standard 61400-1 defined standard turbulence categories based on the value of the characteristic turbulence intensity at 15 m/s. For more information, please see the article on the Turbulence window.
See also
Representative turbulence intensity