Aerodynamic characteristics of wind turbine blade airfoils

This chapter focuses on airfoils for wind turbine blades and their characteristics. The use of panel codes such as XFOIL and RFOIL and CFD codes for the prediction of airfoil characteristics is briefly described. This chapter then discusses the requirements for wind turbine blade airfoils and the effect of leading edge roughness and Reynolds...

Experimental study of the effect of a slat on the aerodynamic performance of a thick base airfoil

There is continuous effort to try and improve the aerodynamic performance of wind turbine blades. This experimental study focusses on the addition of a passive slat on a thick airfoil typically used in the inboard part of commercial wind turbine blades. Nine different slat configurations are considered, with both a clean and tripped main airfoil...

The impact of skinsuit zigzag tape turbulators on speed skating performance

At the 1998 Nagano Winter Olympic Games, zigzag tape was introduced on the race suit lower legs and cap of speed skaters. Application of these zigzag devices on live skaters and cylinders in the wind tunnel showed large improvements in the aerodynamic drag. These wind-tunnel results were unfortunately not widely published, and the impact of...

A simple method to estimate the airfoil maximum drag coefficient

A relatively simple method is presented to predict the maximum two-dimensional drag coefficient of an airfoil only using its shape. The method is based on a contribution related to the leading edge thickness in terms of the y/c coordinate at x/c=0.0125 and a contribution related to the trailing edge flow angle which appears also to be...

Parametric slat design study for thick-base airfoils at high Reynolds numbers

Standard passive aerodynamic flow control devices such as vortex generators and gurney flaps have a working principle that is well understood. They increase the stall angle and the lift below stall and are mainly applied at the inboard part of wind turbine blades. However, the potential of applying a rigidly fixed leading-edge slat element at...

Improved airfoil polar predictions with data-driven boundary-layer closure relations

The accuracy of airfoil polar predictions is limited by the usage of imperfect turbulence models. Can machine-learning improve this situation? Will airfoil polars teach the effect of turbulence on skin-friction? We try to answer these questions by refining turbulence treatment in the Rfoil code: boundary layer closure relations are learned...

Experimental investigation of Surface Roughness effects and Transition on Wind Turbine performance

Aerodynamic experiments have been executed in the wind tunnel and on a wind turbine blade to measure the impact of roughness on the airfoil characteristics and the associated effect on rotor performance and to establish the transition location on a rotating blade. The wind tunnel tests have been performed in the low-speed, low-turbulence wind...

Experimental parameter study for passive vortex generators on a 30% thick airfoil

Passive vane-type vortex generators (VGs) are commonly used on wind turbine blades to mitigate the effects of flow separation. However, significant uncertainty surrounds VG design guidelines. Understanding the influence of VG parameters on airfoil performance requires a systematic approach targeting wind energy-specific airfoils. Thus, the 30...

Probabilistic Design of Airfoils for Horizontal Axis Wind Turbines

We describe a probabilistic approach to design airfoils for wind energy applications. An analytical expression is derived for the probability of perturbations to the operational blade-section angle of attack. It includes the combined influence of wind shear, yaw-misalignment, and turbulence intensity. The theoretical fluctuations in angle of...

Integral Equations for Boundary Layers with Streamwise Vortices

We explore integral boundary layer approximations for shear layer flows with vortex generators. The flow field is decomposed to highlight two phenomena: shear over the wall and vortex-driven mixing of the shear layer. The Navier-Stokes Equations are normalized to identify a new adimensional parameter: the vortex strength number (Vg). Usual...

Gazing at clouds to understand turbulence on wind turbine airfoils

There are many ways to learn from data. Our first experiment consisted in reproducing the way aerodynamicists work [2] with a genetic optimizer. The data pool was too narrow and asymptotic tendencies were unreliable. Our 2nd Experiment, a simple version of [4], had a virtually unlimited data pool and used neural networks. Results were better,...

Experimental benchmark and code validation for airfoils equipped with passive vortex generators

Experimental results and complimentary computations for airfoils with vortex generators are compared in this paper, as part of an e_ort within the AVATAR project to develop tools for wind turbine blade control devices. Measurements from two airfoils equipped with passive vortex generators, a 30% thick DU97W300 and an 18% thick NTUA T18 have been...

Some Results on Bobsleigh Aerodynamics

Bobsleighs races nowadays are decided upon hundredths of a second. As the margins are that small the aerodynamics of a bobsleigh can play a significant role in a race outcome. This paper investigates the influence of the gap between the nose and the rear cowling of a two-man bobsleigh. The paper especially focusses on the misalignment between...

Active stall control for large offshore horizontal axis wind turbines: A conceptual study considering different actuation methods

The increasing size of Horizontal Axis Wind Turbines and the trend to install wind farms further offshore demand more robust design options. If the pitch system could be eliminated, the availability of Horizontal Axis Wind Turbines should increase. This research investigates the use of active stall control to regulate power production in...

Aerodynamic characteristics of wind turbine blade airfoils at high angles-of-attack

Airfoil characteristics at deep stall angles were investigated. It appeared that the maximum drag coefficient as a function of the airfoil upwind y/c ordinate at x/c=0.0125 can be approximated by a straight line. The lift-drag ratios in deep stall of a number of airfoils with moderate lower surface thickness coincide. It was found that the lift...

An overview of NACA 6-digit airfoil series characteristics with reference to airfoils for large wind turbine blades

This paper investigates the NACA 63 and 64 6-digit series of airfoils tested in the NACA LTPT in view to verify the RFOIL calculated airfoil characteristics for high Reynolds numbers. Some anomalies in the zero-lift angles of 15% and 18% thick airfoils from these series are identified, both in the airfoil clean case and in case of wrap-around...

Two-dimensional low-Reynolds number wind tunnel results for airfoil NACA 0018

Airfoil characteristics of rotating wind turbine blades