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Project information
Project description
Boundary layer transition - Theory and DNS
| Research area: |
Fluid mechanics |
| Project members: |
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| Sponsor: |
FOI
VR
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Project description
This project involves research to determine the maximum growth possible of disturbances evolving according to linear theory, as well as to investigate the importance of this growth when non-linearity comes into play. Several shear flow types have been considered. The results show that
non-modal growth, i.e. growth not associated with individual eigenmodes but inherently dependent on their superposition, can cause large transient amplification. This growth is mainly associated with streaky structures in the streamwise direction. Non-linear calculations have shown that when the optimal disturbances from linear theory are used as initial conditions, the threshold amplitudes required for transition to turbulence is lower than for general disturbances. Recent calculations have also shown that these results carry over into the spatial development of disturbances in boundary layers.
Another part of the project involves direct numerical simulations (DNS) of transition to turbulence where these transient growth mechanisms play a major role. This bypass of the traditional Tollmien-Schlichting instability waves is involved in many shear flow transition scenarios. Previously transition associated with localized disturbances have been investigated, and at present the transition in boundary layers starting with a pair of oblique waves is investigated. These waves generate elongated streakss in the streamwise velocity which rapidly grow due to the non-modal mechanism. The secondary instability of these streaks has also been studied, both using DNS and secondary instability theory.
A new direction in the project is to simulate transition in a boundary layer subjected to free-stream turbulence, where the turbulence is initiated close to the leading edge by a random distribution of continuous spectrum modes.
Related articles published in journals or conference proceedings
| Year |
Title |
2003
|
On the convectively unstable nature of optimal streaks in boundary layers
J. Fluid Mech. 221-242 |
2002
|
Weakly nonlinear analysis of boundary layer receptivity to free-stream disturbances
Phys. Fluids 1426-1441 |
2002
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Transition of streamwise streaks in zero presure gradient boundary layers
J. Fluid Mech. 229-262 |
2001
|
On the breakdown of boundary layer streaks
J. Fluid Mech. 29-60 |
2001
|
Stability and transition in shear flows
Springer |
2001
|
A numerical and experimental study of a transitional separation bubble
Aerospace Science and Technology 317-328 |
2000
|
Direct numerical simulations of growth and breakdown of streamwise streaks in flat-plate boundary layer
Proc. 5th Congress Italian Society for Applied and Industrial Mathematics 610-613 |
2000
|
Secondary instability of streaks in boundary layers
Advances in Turbulence VIII. (2000) Proc. 8th European Turbulence Conference, Barcelona, Spain 141-144 |
1999
|
Optimal Disturbances and Bypass Transition in Boundary Layers
Phys. Fluids 134-150 |
1999
|
Numerical and Experimental Investigations of Oblique Boundary Layer Transition.
J. Fluid Mech. 23-57 |
1999
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A nonlinear mechanism for receptivity of free-stream disturbances.
Phys. Fluids 3747-3760 |
1998
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Linear and non-linear development of localized disturbances in zero and adverse pressure gradient boundary-layers.
Phys. Fluids 1405-1418 |
1998
|
The Compressible Inviscid Algebraic Instability for Streamwise Independent Disturbances.
Phys. Fluids 1784-1786 |
1998
|
Secondary instability of cross-flow vortices in Falkner-Skan-Coke boundary layers.
J. Fluid Mech. 339-357 |
1998
|
On stability of streamwise streaks and transition thresholds in plane channel flows.
J. Fluid Mech. 269-303 |
1996
|
Transient growth in compressible boundary layer flow.
Phys. Fluids 826-837 |
1996
|
Comment on "Transition in shear flows. Nonlinear normality versus non-normal linearity"
Phys. Fluids 2257-2258 |
1996
|
Transition Thresholds in boundary layer and channel flows.
Advances in Turbulence VI (Ed. Gavrilakis, S., Machiels, L., Monkewitz, P.A.), Kluwer Academic Publishers 381-384 |
1995
|
Spatial simulations of oblique transition in a boundary layer.
Advances in Turbulence V (Ed. Benzi, R.), Kluwer 31-35 |
1995
|
Bypass transition and linear growth mechanics.
Advances in Turbulence V (Ed. Benzi, R.), Kluwer 190-204 |
1995
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Spatial simulations of bypass transition in boundary layers.
Laminar-Turbulent Transition (Ed. Kobayashi, R.), Springer 263-270 |
1994
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Bounds for threshold amplitudes in subcritical shear flows
J. Fluid Mech. 175-198 |
Internal reports
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