A comparative study of differing vortex structures arising in unsteady separated flows

Examination of forced unsteady separated flow fields on a rotating wind turbine blade

“…A great deal of information regarding unsteady aerodynamics has been gained through research at the University of Colorado [13][14][15][16][17][18][19]. Wind tunnel tests have been conducted for pitching and oscillating wings in constant fre estream velocity.…”

“…This seems reasonable, because the flow would be characterized by deep stall and the boundary layer would be separated throughout the rotation cycle. Reatt achment of the boundary layer has also been shown to be a necessary condition for the generation of a cohesive vortex structure [13][14][15][16][17][18][19]. AOA variations in the post-stall regime, however, did result in weak, diffuse vortex formations, and additional lift compared with static values was observed.…”

“…The formation of discrete, cohesive vortex structures may be considered part of the unsteady separated flow development process. The formation of dynamic stall vortices has been seen in wind tunnel tests for pitching or oscillating airfoils [10][11][12][13][14][15][16][17][18][19]. Although the blades on this particular wind turbine do not pitch or oscillate, yawing of the rotor disk with respect to the wind, sudden wind gusts, or passage through the wake of a cylindrical tower may produce geometrically similar effects.…”

“…A simple physical model is propo sed, based on a wing sinusoidally oscillating in pitch. It was shown earlier in this report that thi s effective motion approximates the actual motion that the blade experiences.It has been demonstrated by McCroskey[11], Huyer et al[13], and Robinson[15] that complex vortical flow fields are produced by sinusoidally oscillating wings. These vortices leave identifiable signatures in the pressure distributions that allow them to be tracked.…”

Examination of forced unsteady separated flow fields on a rotating wind turbine blade

“…The formation of discrete, cohesive vortex structures may be considered part of the unsteady -__ separated flow development process. The formation of dynamic stall vortices has been seen in wind _ tunnel tests fbr pitching or oscillating airfoils [10][11][12][13][14][15][16][17][18][19]. Although the blades on this particular wind turbine do not pitch or oscillate, yawing of the rotor disk with respect to the wind, sudden wind gusts, or passage through the wake of a cylindrical tower may produce geometrically similar effects.…”