Aerodynamic Effects of Roughness on Wind Turbine Blade Sections

Abstract

This work describes an investigation into the aerodynamic effects of the painted surface roughness of manufactured wind turbine blades. Fetches of wavy, orange-peel type roughness typical of new blades were applied to two DU96-W-180 models of chord lengths 0.46-m and 0.80-m. Lift, drag and transition location were measured at chord Reynolds Numbers ranging from 1.5x10 6 to 3.0x10 6 . For all cases, the results showed that with increasing roughness Reynolds Number the lift decreases, the drag increases and transition moves forward. These effects appear to increase gradually with the roughness Reynolds Number, up to a critical roughness Reynolds Number between 20 and 25. After this critical roughness Reynolds Number the effects of the roughness on lift, drag and transition become more distinct. The changes in transition are attributed to rapid growth of Tollmien-Schlichting waves brought on by roughness elements of matching scale. It was also found that the decrease in drag is almost exclusively due to the forward shift of the transition region and not due to increased drag on the roughness elements themselves. These findings show that the surface roughness of even new highly loaded lifting surfaces cannot be assumed negligible.

Laser Displacement Sensors for Wind Tunnel Model Position Measurements

“…This technique also showed a small amount of model bending (<2 mm). Previous studies with this model [12,13] have shown that boundary layer transition and other aerodynamic qualities do not vary in the span (z) direction, which suggests that this model bending does not affect the model aerodynamics. However, the bending is enough to bias the single laser angle of attack measurement.…”

“…For this work, a 0.8 m chord DU96-W-180 airfoil model was installed into the test section shown in Figure 1b. This model, which has been used in a number studies at the VT SWT [12,13], was constructed at Virginia Tech by the Aerospace and Ocean Engineering Machine Shop. The model is constructed of 50-mm thick CNC-machined aluminum laminates.…”