Location of Repository

Direct numerical simulations of forced and unforced separation bubbles on an airfoil at incidence

By L.E. Jones, R.D. Sandberg and N.D. Sandham


Direct numerical simulations (DNS) of laminar separation bubbles on a NACA-0012 airfoil at Re-c = 5 x 10(4) and incidence 5 degrees are presented. Initially volume forcing is introduced in order to promote transition to turbulence. After obtaining sufficient data from this forced case, the explicitly added disturbances are removed and the simulation run further. With no forcing the turbulence is observed to self-sustain, with increased turbulence intensity in the reattachment region. A comparison of the forced and unforced cases shows that the forcing improves the aerodynamic performance whilst requiring little energy input. Classical linear stability analysis is performed upon the time-averaged flow field; however no absolute instability is observed that could explain the presence of self-sustaining turbulence. Finally, a series of simplified DNS are presented that illustrate a three-dimensional absolute instability of the two-dimensional vortex shedding that occurs naturally. Three-dimensional perturbations are amplified in the braid region of developing vortices, and subsequently convected upstream by local regions of reverse flow, within which the upstream velocity magnitude greatly exceeds that of the time-average. The perturbations are convected into the braid region of the next developing vortex, where they are amplified further, hence the cycle repeats with increasing amplitude. The fact that this transition process is independent of upstream disturbances has implications for modelling separation bubbles

Topics: TL
Year: 2008
OAI identifier: oai:eprints.soton.ac.uk:55698
Provided by: e-Prints Soton

Suggested articles



  1. (2003). A combined experimental/numerical study of unsteady phenomena in a laminar separation bubble.
  2. (1957). A correlation of low-speed airfoil-section stalling characteristics with Reynolds number and airfoil geometry.
  3. (1969). A semi-empirical theory for the growth and bursting of laminar separation bubbles.
  4. (1999). A stable and conservative interface treatment of arbitrary spatial accuracy.
  5. (1985). Absolute and convective instabilities in free shear layers.
  6. (2003). Advances in global linear instability analysis of nonparallel and three-dimensional flows.
  7. (1986). B e r n a l ,L .P .&R o s h k o ,A
  8. (1992). Compact finite difference schemes with spectral-like resolution.
  9. (1998). Cooperative elliptic instability of a vortex pair.
  10. (2000). Direct numerical simulation of shortlaminar separation bubbles with turbulent reattachment.
  11. (2007). Direct numerical simulations of trailing-edge noise generated by boundary-layer instabilities.
  12. (1988). Direct simulation of a turbulent boundary layer up to Rθ =1410.
  13. (2004). Effect of spanwise-modulated disturbances on transition in a separated boundary layer.
  14. (2002). Entropy splitting for high-order numerical simulation of compressible turbulence.
  15. (1981). Hydrodynamic Stability.
  16. (2004). Investigations on controlled transition development in a laminar separation bubble by means of LDA and PIV.
  17. (1998). Local and global instability properties of separation bubbles.
  18. (2000). Mechanisms of transition and heat transfer in a separation bubble.
  19. (1994). Nonlinear effects of 2D and 3D disturbances on laminar separation bubbles.
  20. (2004). Numerical investigation of transitional and turbulent backward-facing step flows.
  21. (1989). Numerical simulation of the absolutely and convectively unstable wake.
  22. (2000). On the origins of unsteadiness and three-dimensionality in a laminar separation bubble.
  23. (1990). On the three-dimensional instability of strained vortices.
  24. (1990). P a u l e y ,L .L . ,M o i n ,P .&R e y n o l d s
  25. R i s t ,U .&M a u c h e r ,U .2002 Investigations of time-growing instabilities in laminar separation bubbles.
  26. (1994). Response of two-dimensional separation to three-dimensional disturbances.
  27. (2006). S a n d b e r g ,R .D .&S a n d h a m ,N .D
  28. (2001). S c h m i d ,P .J .&H e n n i n g s o n
  29. (1997). Secondary instabilities in a laminar separation bubble.
  30. (1978). Series representation of the eigenvalues of the Orr-Sommerfeld equation.
  31. (1992). The natural and forced formation of spot-like’vortex dislocations’ in the transition of a wake.
  32. (2001). The physical mechanism of transition in bluff body wakes.
  33. (1967). The structure and behaviour of separation bubbles.
  34. (1996). Three-dimensional Floquet stability analysis of the wake of a circular cylinder.
  35. (1998). Three-dimensional instabilities in wake transition.
  36. (1996). Three-dimensional wake transition.
  37. (1998). Transitional structures in a laminar separation bubble.
  38. (1987). Viscous-inviscid analysis of transonic and low Reynolds number airfoils.
  39. (1993). Vortex generators used to control laminar separation bubbles.
  40. (2006). Wall pressure and shear stress spectra from direct simulations of channel flow.

To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.