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Experimental Study of Boundary Layer Transition on a Swept Wing

Masdari, Mehran | 2011

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 42895 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Soltani, Mohammad Reza; Ghorbanian, Kaveh
  7. Abstract:
  8. Swept wings are of great interest for achieving high speed as well as increasing the critical Mach number in aircrafts and unmanned flying vehicles. The governing fluid mechanical phenomenon on swept wings is strongly influenced by the chordwise and spanwise components of the cross-flow. Laminar airfoils are employed for drag reduction and postponing the boundary layer transition from laminar to turbulence. Hence, the knowledge about the boundary layer structure and instability modes is of great significance. A series of wind tunnel tests are performed to examine the flow field over a swept wing at various conditions. The wing has a laminar flow airfoil section similar to NACA 6-series ones. Static pressure distributions over the upper surface of the wing in both chordwise and spanwise directions and boundary layer profiles are measured at different angles of attack for three wings with sweep angle of 23, 33, and 40 degrees. The data is employed to predict the transition point at each chordwise section. Standard deviation parameter of the pressure data and Hot-film voltages shows that this factor reaches to maximum value in the transition region. The power spectral density calculated from the total pressure data of the boundary layer over the wing surface at several locations shows the instability modes. Results indicate that the instability modes in the boundary layer of the wing consist of three modes: TS, stationary crossflow, and travelling crossflow where the stationary mode is dominant compared to the other modes. Further, the pressure distribution plays a major role on the strength of this mode. Finally, the effect of the stationary mode increases with sweep angle of 40 degrees.
  9. Keywords:
  10. Boundary Layer ; Boundary Layer Transition ; Swept Wing ; Frequency Analysis ; Standard Deviation

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