What is the critical height of leading edge roughness for aerodynamics?

Christian Bak,Emil K Kruse,Anders S Olsen,Mac Gaunaa

doi:10.1088/1742-6596/753/2/022023

Abstract

In this paper the critical leading edge roughness height is analyzed in two cases: 1) leading edge roughness influencing the lift-drag ratio and 2) leading edge roughness influencing the maximum lift. The analysis was based on wind tunnel measurements on the airfoils NACA0015, Risoe-B1-18 and Risoe-C2-18 and at three different Reynolds numbers with two different leading edge roughness tape heights. Firstly, an analysis of the momentum thickness as function of Reynolds number was carried out based on the boundary layer theory by Thwaites. Secondly, the wind tunnel measurements combined with panel code predictions of the boundary layer momentum thickness created the basis for determining the impact of roughness on the aerodynamic performance. The critical heights were related to the Reynolds numbers and thereby the size of the wind turbines.

Highlights

Irregular and non-smooth surfaces at the leading edge of wind turbine blades can cause a loss of energy production
The wind tunnel measurements combined with panel code predictions of the boundary layer momentum thickness created the basis for determining the impact of roughness on the aerodynamic performance
In this paper the critical leading edge roughness height was analyzed in two cases: 1) where the lift-drag ratio is not changed and 2) where the maximum lift is not changed

Summary

Introduction

Irregular and non-smooth surfaces at the leading edge of wind turbine blades can cause a loss of energy production. For many years there has been a focus on leading edge roughness (LER) from the wind turbine industry, and from e.g. the aviation industry. This is because it is known that LER can cause reduced aerodynamic performance, e.g. Sareen et al [4] concludes that the loss in annual energy production could be as high as 25% if severe roughness appears at the leading of a blade. This is the reason that leading edge roughness is an important issue

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Conclusion