The influence of free-stream turbulence intensity on the performance of Gurney-flap equipped wind-turbine blades

Conference · Tue Oct 01 04:00:00 EDT 1996

OSTI ID:372130

Kentfield, J A.C. ^[1]

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1. Univ. of Calgary, Alberta (Canada). Dept. of Mechanical Engineering

A study is presented of apparent drag anomalies based on the results of measurements made by many workers. In some cases the addition, to an airfoil, of a Gurney flap adds little or nothing to the airfoil drag coefficient; yet in other cases, for a prescribed Gurney-flap height-to-chord ratio, the addition of the Gurney flap can increase the airfoil drag coefficient,m at low lift coefficients, by a factor as large as three. The lift increment obtained is essentially independent of the drag level recorded and is, to a first approximation, proportional to the height-to-chord ratio of the Gurney flap. It is, as a consequence of the study, shown that the major adverse influence on the drag coefficient of Gurney-flap equipped airfoils is the thinness of the pressure-surface boundary layer at the airfoil trailing edge. It has been shown by other workers that provided the height of a Gurney flap is less than the boundary layer thickness, the drag penalty due to the Gurney flap is small or can be essentially zero. The influence of the chord-based Reynolds number on the pressure-surface boundary layer thickness appears to parallel that associated with a turbulent flow over a flat plate. Hence the boundary layer thickness diminishes with increasing chord-based Reynolds number. A factor that is shown to have a major impact on the boundary layer thickness is the inherent turbulence level of the approaching flow. Generally, the higher the turbulence level and the lower the Reynolds number, the thicker, for a prescribed airfoil chord, the boundary layer.

• OSTI ID: 372130
• Report Number(s): CONF-960154--; ISBN 0-9648731-8-4
• Country of Publication: United States
• Language: English

Related Subjects

17 WIND ENERGY
AERODYNAMICS
AUGMENTATION
PERFORMANCE
TURBULENCE
WIND TURBINES