Presentations

Abstract

Directional variations in design turbulence intensity (freestream and wake-added turbulence) affect support structure loads and thereby design lifetime estimates. When performing Site Conditions Assessments, it is therefore necessary to characterise turbulence conditions directionally. This task is made difficult due to the general lack of site-specific cup or sonic anemometer measurements. Furthermore, it is usual practice to apply the results of wind farm turbulence calculations as omnidirectional inputs to load calculations. The purpose of this work is twofold. We first present a methodology for providing accurate, site-specific directional TI assessments which does not require measurements at the site using a simple analytical model already presented and validated at multiple locations, which accounts for the atmospheric stability conditions at the site. Then, we provide evidence that variations in freestream turbulence (primarily related to atmospheric stability) and wake-added turbulence (related to turbine aerodynamics and layout geometry) need to be accounted for in design, and that approaches using omnidirectional descriptions lead to less accurate design fatigue loads.