Abstract

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The flow field over a NREL S826 airfoil subjected to different ice accretions has been investigated by particle image velocimetry for angles of attack ranging from −4 • to 16 • . The results have been compared to previously acquired force measurements. For streamlined ice accretions, increased surface roughness and changes to the combined airfoil-ice geometry lead to reduced aerodynamical performance of the airfoil. However, the streamlined ice accretions might act as leading edge flaps at high angles of attack, delaying stall. For the horn ice accretion, a large separation bubble occurs behind the horn reducing the performance of the airfoil, and initiating stall at a lower angle of attack compared to the other cases.

This study investigated the mean velocity of the near-field wake of a lab-scale wind turbine subjected to seven different incoming turbulent shear flows through particle image velocimetry. An active grid was used to generate the incoming flows with a novel actuation method that decoupled shear from turbulence intensity. The wake geometry relative to the incoming flows is symmetric and not significantly impacted by shear. A slight reduction in the relative wake velocity deficit was observed at x/D = 2 for higher levels of freestream turbulence intensity. The hub velocity contour line was deflected towards the high-velocity side by shear upstream of the rotor. In the wake, higher local shear forced this contour line away from the rotor tip and towards the hub.