Unsteady Aerodynamics Associated with a Horizontal-Axis Wind Turbine

The wind turbine industry is currently facing many difficulties constructing efficient wind turbine machines caused by the inability to adequately predict structural loading and power output. Available evidence from wind turbines in a field environment suggests that formation of complex unsteady separated flowfields may be responsible for many aspects of wind turbine component failure. To examinethis possibility in more detail, the Combined Experiment was developed. A full-scale wind turbine was constructed and operated in a field environment. The environment chosen was subject to wide variations in wind speed and direction and subsequently generated an extensive set of data for a variety of inflow test conditions. A single wind turbine blade was instrumented with pressure transducersand strain gauges with several data sets collected across a wide spectrum of typical and limiting wind turbine operating conditions. Surface pressure data taken at various spanwise locations along the blade demonstrated highly transient and spatially complex aerodynamic behavior for even the most basic operating conditions. Integrated normal force coefficient data showed enhanced lift valuessignificantly beyond that predicted from steady-state two-dimensional wind-tunnel test data. Surface pressure data and integrated moment coefficient data suggested formation of coherent vortices consistent with the dynamic stall process observed in wind-tunnel tests for pitching wings. The unsteady, three-dimensional aerodynamic behavior for this wind turbine was then discussed and summarized.