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Study of Reduced Frequency Effects on Wind Tunnel Wall Pressure for a Plunging Airfoil

Mohammadi, Zeynab | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40497 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Soltani, Mohammad Reza
  7. Abstract:
  8. The unsteady phenomena occur in rotors of helicopters, wind turbines and compressors. Investigation of the unsteady flow is a very important test, since it can affect and restrict the performance of rotors of helicopters and wind turbine's blades when operating at high angles of attack. Dynamic tests, such as pitching and plunging oscillations are one of the best methods for studying these phenomena due to the complexity of the unsteady flows. In analyzing the results of dynamic tests one must consider the interference effects of wind tunnel walls. Different investigations show that in dynamic tests, the interference effects of flow field around the model, wind tunnel walls and support of the model, can not be ignored; then the effects should be considered in all measurements. Meanwhile, because of complex relation between the interferential effects and sources of unsteady in the dynamic tests, it is not possible to use the existing theories. Therefore, in this work the flow field close to the walls during the plunging motion of a 2-D model airfoil of a 660 KW wind turbine's blade has been studied. For this purpose, static pressure distribution on the lower surface and side walls of wind tunnel test section was measured via pressure transducers and the effects of reduced frequency, Reynolds number in term of free stream speed, oscillation amplitude and mean angle of attack on the pressure distribution were investigated. Measurements were done at amplitudes of ±3.5, ±5, ±8 cm and frequencies of 1.75, 2.26, 3.14 and 4.03 Hz. Free stream velocity was changed from 30 to 60 m/s. Tests were carried out at three zone: before, near and after the dynamic stall of the model. For this purpose mean angles of attack were; 5, 10 and 18 degree. The results were also compared with those of the pitching motions. Results show that the most important parameter affected the pressure distribution of wind tunnel walls is the reduced frequency. Increasing this parameter could enhance effects of non-circulatory terms against the circulatory terms in the unsteady flows. As the velocity increases, the effect of Reynolds number could be seen as reduce in the fluctuations. Finally, it is seen that the flow field is affected by the plunging motion of the model more than the corresponding pitching motion.

  9. Keywords:
  10. Unsteady Aerodynamic ; Reduced Frequency ; Plunging ; Tunnel Wall Interference ; Tunnel Wall Pressure Distribution

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