Turbulent Intensity
Turbulence Intensity (I) is a dimensionless measure of turbulence strength, defined as the ratio of the standard deviation of wind speed fluctuations to the mean wind speed. It’s expressed as:
$$ I = \frac{u’}{U_{\text{local}}} $$
Where:
$u′$ is the root-mean-square of the turbulent wind speed fluctuations
$U_{\text{local}}$ is the local mean wind speed
Non-linear Relationship with Wind Speed
Turbulence Intensity does not increase linearly with wind speed. This non-linear relationship is due to several factors:
- Atmospheric Stability: As wind speed increases, the atmosphere becomes more neutrally stable, which can lead to a decrease in turbulence intensity.
- Surface Roughness: The effect of surface roughness on turbulence becomes relatively less significant at higher wind speeds.
- Mechanical Turbulence: At very high wind speeds, mechanical turbulence generated by wind shear may become more dominant than thermal turbulence.
Importance of Turbulence Intensity
Understanding Turbulence Intensity is essential for several applications:
- Wind Energy: High turbulence intensity affects the performance and lifespan of wind turbines.
- Aviation: Turbulence intensity is crucial for flight safety and planning, as high turbulence can impact aircraft stability and passenger comfort.