Determination of Wind Shear Coefficients and Conditions of Atmospheric Stability for Three Iraqi Sites

Abstract

The coefficient of wind shear at low and high frequencies, from diurnal and seasonal variations to disturbance caused by weather patterns, is subject to temporal fluctuations, but in many cases, the coefficient of wind shear assumed as a constant. This presumption causes major resource management errors, raises instability in projects and potentially affects the ability to control the wind turbines connected to the grid. Hourly average of 10 m wind speed with a standard (50 m) height employed to estimate the WSC with the well-known power equation for the wind profile law. This paper estimates WSC from wind speed data on three sites in Iraq. Monthly wind speed and wind direction changes were determined for these locations. The variations of WSC in one year are (0.23, 0.2, and 0.35) for Al-Shehabi, Al-Najaf, and Al-Fajer respectively. In the summer months (June to September) it is obvious that average wind speeds in all select areas increase while in other seasons they are almost decreasing. The WSC had neural diurnal and monthly variations. Due to the increased temperature at this period of year, WSC has decreased at mid-day, and this is valid for all studied site during the winter and summer days. The stability of atmosphere conditions was determined as stable, stable, and strongly stable for Al-Shehabi, Al-Najaf and Al-Fajer sites respectively.