Abstract
Aerodynamic performance of two small-scale horizontal axis wind turbines are analyzed under the extreme operating gust and extreme direction change conditions with initial wind speeds of 7, 10, 13, 15 and 20 m/s. Performance predictions are performed using computational fluid dynamics, and time variations of shaft torque and hub bending moment produced by the turbines are presented and compared with each other. Sectional flow field and sectional blade loading details along with surface skin friction line predictions are also presented in order to explain the loading behavior of the turbine blades at the mentioned extreme wind conditions. Predictions show that variations in wind speed and blade loadings are similar at low wind speeds, however, this similarity degrades as the wind speed increases. Also compared to wind speed changes, aerodynamic forces are shown to adapt more slowly to wind direction changes
Highlights
Wind turbine blades are aerodynamically designed by searching for suitable design parameters that maximize the energy production at low cost [1]
Two of the extreme wind conditions specified in this standard are the extreme operating gust (EOG) where wind speed experiences transient oscillations and the extreme direction change (EDC) where the yaw error gradually increases from zero to a positive value
In order to use the same mesh for both of the extreme wind speed cases, the mesh was constructed for the full geometry in order to account for non-symmetry that would occur for the EDC case
Summary
Wind turbine blades are aerodynamically designed by searching for suitable design parameters that maximize the energy production at low cost [1]. The annual energy production of turbine at a given wind site should be calculated for this purpose. Steady state or time averaged power values produced at corresponding wind speeds are used in annual energy production calculations [3] -[9]. International Standard IEC 61400-1 outlines the minimum design requirements for horizontal axis wind turbines (HAWT) [12]. According to this standard, performance of a turbine and loading on its blades at extreme wind conditions is one of the elements that must be considered in order to ensure proper safety and reliability. Two of the extreme wind conditions specified in this standard are the extreme operating gust (EOG) where wind speed experiences transient oscillations and the extreme direction change (EDC) where the yaw error gradually increases from zero to a positive value
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