Location of Repository

Direct numerical simulation of 'short' laminar separation bubbles with turbulent reattachment

By M. Alam and N.D. Sandham


Direct numerical simulation of the incompressible Navier–Stokes equations is used to study flows where laminar boundary-layer separation is followed by turbulent reattachment forming a closed region known as a laminar separation bubble. In the simulations a laminar boundary layer is forced to separate by the action of a suction profile applied as the upper boundary condition. The separated shear layer undergoes transition via oblique modes and [Lambda]-vortex-induced breakdown and reattaches as turbulent flow, slowly recovering to an equilibrium turbulent boundary layer. Compared with classical experiments the computed bubbles may be classified as ‘short’, as the external potential flow is only affected in the immediate vicinity of the bubble. Near reattachment budgets of turbulence kinetic energy are dominated by turbulence events away from the wall. Characteristics of near-wall turbulence only develop several bubble lengths downstream of reattachment. Comparisons are made with two-dimensional simulations which fail to capture many of the detailed features of the full three-dimensional simulations. Stability characteristics of mean flow profiles are computed in the separated flow region for a family of velocity profiles generated using simulation data. Absolute instability is shown to require reverse flows of the order of 15–20%. The three-dimensional bubbles with turbulent reattachment have maximum reverse flows of less than 8% and it is concluded that for these bubbles the basic instability is convective in nature

Topics: QA, QC
Year: 2000
OAI identifier: oai:eprints.soton.ac.uk:21333
Provided by: e-Prints Soton

Suggested articles



  1. (1994). A comparison study of an improved temporal DNS and spatial DNS of compressible boundary layer transition.
  2. (1967). A semi-empirical theory for the growth and bursting of laminar separation bubbles. ARC Conf.
  3. (1985). Absolute and convective instabilities in free shear layers.
  4. (1995). Absolute and convective instabilities in separation bubbles.
  5. (1985). Analysis of transitional separation bubbles on in swept wings.
  6. (1996). Boundary layer relaxation after a separated region. Expl Thermal Fluid Sci.
  7. (1980). Calculation of laminar separation bubbles and their eect on aerofoil performance.
  8. (1997). Direct and Reynolds-averaged numerical simulation of a transitional separation bubble. 11th Symp. on Turbulent Shear Flows,
  9. (1994). Direct numerical simulation of aerofoil separation bubbles.
  10. (1998). Direct numerical simulation of laminar separation bubbles. PhD Dissertation, Queen Mary and West College,
  11. (1997). Direct numerical simulation of turbulent flow over a backward-facing step.
  12. (1994). Direct simulation of a self-similar mixing layer.
  13. (1988). Direct simulation of a turbulent boundary layer up to Re
  14. (1998). Direct simulation of turbulence using massively parallel computers.
  15. (1993). Experimental and numerical study of a turbulent boundary layer with pressure gradients.
  16. (1968). Growth of disturbances in both space and time.
  17. (1968). Laminar separation in two and three-dimensional incompressible flow.
  18. (1990). Local and global instabilities in spatially developing flows.
  19. (1998). Local and global instability properties of separation bubbles.
  20. (1996). Low-Reynolds-number separation on an aerofoil.
  21. (1994). Nonlinear eects of two-dimensional and three-dimensional disturbances on laminar separation bubbles.
  22. (1998). Numerical study of separation bubbles with turbulent reattachment followed by a boundary layer relaxation.
  23. (1953). O w e n ,P .R .&K l a n f e r ,L
  24. (1963). On stability of parallel flows and the behaviour of separation bubbles.
  25. (1988). Onflow/outflow boundary conditions and global dynamics of spatial mixing layers.
  26. (1981). Propagation of linear wave packets in laminar boundary layers.
  27. (1967). Res.
  28. (1997). Simulation and modelling of the skew response of turbulent channel flow to spanwise flow deformation.
  29. (1997). Simulations of laminar and transitional separation bubbles. TR S-100 44. Royal Inst. of Tech.,
  30. (1966). Some results of investigation of separation bubbles.
  31. (1998). Spatial direct numerical simulation of compressible boundary layer flow. Thesis, Universiteit Twente,
  32. (1988). Spectral Methods in Fluid Dynamics.
  33. (1969). Structure and behaviour of laminar separation bubbles.
  34. (1991). The kinematics of turbulent boundary layer structure.
  35. (1992). The late stages of transition to turbulence in channel flow.
  36. (1972). The reattachment and relaxation of a turbulent shear layer.
  37. (1993). The stability of the flow in a laminar separation bubble.
  38. (1955). The structure of turbulence.
  39. (1990). The structure of two-dimensional separation.
  40. (1993). The unsteady structure of two-dimensional separation.
  41. (1980). Treatment of incompressibility and boundary layer conditions in three-dimensional numerical spectral simulations of plane channel flows.
  42. (1987). Turbulent statistics in fully developed channel flow at low Reynolds number.
  43. (1995). Two-dimensional large eddy simulation of a transitional separation bubble.

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