Search: onr:"swepub:oai:DiVA.org:kth-23881" >
Transition in bound...
Transition in boundary layers subject to free-stream turbulence
-
- Brandt, Luca (author)
- KTH,Mekanik
-
- Schlatter, Philipp (author)
- KTH,Mekanik
-
- Henningson, Dan S. (author)
- KTH,Mekanik
-
(creator_code:org_t)
- Cambridge University Press (CUP), 2004
- 2004
- English.
-
In: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 517, s. 167-198
- Related links:
-
https://urn.kb.se/re...
-
show more...
-
https://doi.org/10.1...
-
show less...
Abstract
Subject headings
Close
- The effect of high levels of free-stream turbulence on the transition in a Blasius boundary layer is studied by means of direct numerical simulations, where a synthetic turbulent inflow is obtained as superposition of modes of the continuous spectrum of the Orr-Sommerfeld and Squire operators. In the present bypass scenario the flow in the boundary layer develops streamwise elongated regions of high and low streamwise velocity and it is suggested that the breakdown into turbulent spots is related to local instabilities of the strong shear layers associated with these streaks. Flow structures typical of the spot precursors are presented and these show important similarities with the flow structures observed in previous studies on the secondary instability and breakdown of steady symmetric streaks. Numerical experiments are performed by varying the energy spectrum of the incoming perturbation. It is shown that the transition location moves to lower Reynolds numbers by increasing the integral length scale of the free-stream turbulence. The receptivity to free-stream turbulence is also analysed and it is found that two distinct physical mechanisms are active depending on the energy content of the external disturbance. If low-frequency modes diffuse into the boundary layer, presumably at the leading edge, the streaks Lire induced by streamwise vorticity through the linear lift-up effect. If, conversely, the free-stream perturbations are mainly located above the boundary layer a nonlinear process is needed to create streamwise vortices inside the shear layer. The relevance of the two mechanisms is discussed.
Subject headings
- NATURVETENSKAP -- Fysik (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences (hsv//eng)
Keyword
- orr-sommerfeld equation
- near-wall turbulence
- self-sustaining process
- bypass transition
- continuous-spectrum
- shear flows
- localized disturbances
- optimal perturbations
- channel flows
- receptivity
Publication and Content Type
- ref (subject category)
- art (subject category)
Find in a library
To the university's database