On the Influence of trip strips on Rotor Blade Measurements

The current paper discusses the effect of fixing transition on a three-bladed upwind horizontal axis wind turbine with a rotor diameter of 3 m located in a wind tunnel with a cross-section of 4.2 m x 4.2 m. The turbine is analysed at rated condition and below the rated operating point. The transition is fixed on the blades by means of a zigzag tape trip strip. A comparison between the fixed transition and a clean case, without any trip strip, is made in terms of the angle of attack, relative velocity, and local forces and moments. Additionally, the zigzag tape application method is studied. The results are obtained from surface pressure taps and one 3-hole probe located at 45% and 85% of the blade span, respectively. The inclusion of the zigzag tape shows slight variations on the relative velocity, up to 1%. The angle of attack has an average increment of 0.5° when the transition is forced. The local forces and pitch moment can vary up to 23%, depending on the implementation and the operational condition.