Loading...

Experimental Study of Transition on an Airfoil in Pitching-Plunging Motion

Akhlaghi, Hassan | 2020

401 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54452 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Soltani, Mohammad Reza; Maghrebi, Mohammad Javad; Ghorbanian, Kaveh
  7. Abstract:
  8. Laminar-to-turbulent transition is very important concept in fluid dynamics due to its significant role on skin friction drag and heat transfer. It is more important in the fluid-based systems such as wind turbines. Employing computational fluid dynamics is still not efficient on prediction of flow transition, especially in complex problems such as oscillating airfoils. In one hand, flow transition models are not still suitable for general engineering flows such as oscillating airfoils. On other hand, due to the lack of experimental data, the existing flow solvers have not proven in the accurate simulation of the flow field simulation for complex problems such as oscillating airfoils. This shows the importance of the experimental study of the flow transition in complex systems. One example of such complex systems is airfoils in combined pitch-plunge oscillation. This type of airfoil could be observed in the outer blade sections of the horizontal-axis wind turbines. Accurate flow transition detection over wind turbine blades enables the engineers to improve the blade profile for optimum performance or to employ suitable flow control mechanisms for achieving largest laminar flow region over the blades. In this dissertation, the experimental study of laminar-to-turbulent transition over a blade section of a 660 kW wind turbine is considered. The section is located at 16m from the hub of a 23.5m wind turbine blade. To do so, a 2D airfoil model has been employed to experimentally investigate the boundary-layer transition during static, pitch, plunge, and pitch-plunge motions. This study is based on the wall shear stress data from hot-film sensors, surface pressure distribution and wake pressure distribution from pressure transduces. In the first step, the methods for detection of boundary layer phenomena based on the hot-film sensors and pressure transducers are reviewed, created, and validated. Then, the transitional boundary layer in different oscillation types is considered. The effects of different motion parameters and flow conditions have been considered on the transitional boundary layer phenomena, especially transition point. These results could be employed to develop and verify the transition models for oscillating airfoils. Based on the obtained results, the employed and developed techniques is suitable for determination of the transitional boundary layer features. Combined pitch-plunge motion leads to the higher width for Aerodynamic load, transition onset, and laminar separation points hysteresis loops. It is shown that the plunge motion delays the transition and extends the laminar flow region for oscillations within and beyond the static stall angle of attack
  9. Keywords:
  10. Experimental Investigation ; Oscillating Airfal ; Pitching Oscillation ; Plunging ; Pressure Transducers ; Hot Film Sensor ; Combined Pitch-Plunge Oscillation ; Laminar-to-Turbulent Transition

 Digital Object List

 Bookmark

No TOC