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Experimental Study of Transition on an airfoil in Plunging Motion

Rasi Marzabadi, Faezeh | 2011

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 42569 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Soltani, Mohammad Reza
  7. Abstract:
  8. Prediction of the location of transition point is important for wind turbine applications. The laminar/turbulent properties of the flow field have an important influence on the skin friction and separation location that affect both lift and drag characteristics of the blade significantly. In this study, a series of experiments were conducted on a section of a 660 kW wind turbine blade in subsonic flow. Boundary layer transition point was measured using multiple hot-film sensors. Hot-film data were analyzed in both time and frequency domains. The experiments involved static and dynamic tests where the airfoil motion was of plunging type oscillation. The effects of several parameters such as reduced frequency and mean angle of attack were investigated. Further, the effect of leading-edge roughness on the state of the boundary layer that simulates surface irregularities on the wind turbine blades was studied. By increasing the angle of attack, disturbances and transition location moved toward the leading edge. The dynamic data showed hysteresis between the transition location in the upstroke and down-stroke motions. Boundary layer transition occurred earlier for increasing rather than for decreasing the effective angle of attack due to the adverse moving wall effects for the plunging airfoil motion. Increasing the mean angle of attack resulted in shifting the transition region toward the leading edge. The effect of reduced frequency was promoting the boundary layer transition to turbulent one during the upstroke motion. Surface roughness moved the transition point toward the leading edge and caused early trailing edge turbulent separation which results in reducing the effectiveness of the airfoil. Boundary layer instability frequencies were dominated through transition
  9. Keywords:
  10. Plunging ; Reduced Frequency ; Surface Roughness ; Airfoil ; Boundary Layer Transition

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