DNS study on mechanism of small length scale generation in late boundary layer transition

2012 ◽  
Vol 241 (1) ◽  
pp. 11-24 ◽  
Author(s):  
Ping Lu ◽  
Chaoqun Liu
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Transition ◽  
Length Scale ◽  
Small Length ◽  
Layer Transition ◽  
Small Length Scale

scholarly journals New Theories on Boundary Layer Transition and Turbulence Formation

2012 ◽  
Vol 2012 ◽  
pp. 1-22 ◽  
Author(s):  
Chaoqun Liu ◽  
Ping Lu ◽  
Lin Chen ◽  
Yonghua Yan
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Shear Layer ◽  
Boundary Layer Transition ◽  
Length Scale ◽  
Multiple Level ◽  
Shear Layer Instability ◽  
Small Length ◽  
Layer Transition ◽  
Turbulence Generation

This paper is a short review of our recent DNS work on physics of late boundary layer transition and turbulence. Based on our DNS observation, we propose a new theory on boundary layer transition, which has five steps, that is, receptivity, linear instability, large vortex structure formation, small length scale generation, loss of symmetry and randomization to turbulence. For turbulence generation and sustenance, the classical theory, described with Richardson's energy cascade and Kolmogorov length scale, is not observed by our DNS. We proposed a new theory on turbulence generation that all small length scales are generated by “shear layer instability” through multiple level ejections and sweeps and consequent multiple level positive and negative spikes, but not by “vortex breakdown.” We believe “shear layer instability” is the “mother of turbulence.” The energy transferring from large vortices to small vortices is carried out by multiple level sweeps, but does not follow Kolmogorov's theory that large vortices pass energy to small ones through vortex stretch and breakdown. The loss of symmetry starts from the second level ring cycle in the middle of the flow field and spreads to the bottom of the boundary layer and then the whole flow field.

A Boundary Layer Transition Model

1996 ◽  
Author(s):  
Mark W. Johnson ◽  
Ali H. Ercan
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Transition ◽  
Test Cases ◽  
Length Scale ◽  
Transition Model ◽  
Freestream Turbulence ◽  
Layer Transition ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
Turbulent Length Scale

A new boundary layer transition model is presented which relates the velocity fluctuations near the wall to the formation of turbulent spots. A relationship for the near wall velocity frequency spectra is also established, which indicates an increasing bias towards low frequencies as the skin friction coefficient for the boundary layer decreases. This result suggests that the dependence of transition on the turbulent length scale is greatest at low freestream turbulence levels. This transition model is incorporated in a conventional boundary layer integral technique and is used to predict eight of the ERCOFTAC test cases. Three of these test cases are for nominally zero pressure gradient and the remaining five are for a pressure distribution typical of an aft loaded turbine blade. The model is demonstrated to predict the development of the boundary layer through transition reasonably accurately for all the test cases. The sensitivity of start of transition to the turbulent length scale at low freestream turbulence levels is also demonstrated.

Boundary-layer transition by interaction of discrete and continuous modes

2008 ◽  
Vol 604 ◽  
pp. 199-233 ◽  
Author(s):  
YANG LIU ◽  
TAMER A. ZAKI ◽  
PAUL A. DURBIN
Keyword(s):  
Boundary Layer ◽  
Finite Amplitude ◽  
Secondary Instability ◽  
Boundary Layer Transition ◽  
Length Scale ◽  
Bypass Transition ◽  
Continuous Mode ◽  
Layer Transition ◽  
Boundary Layer Turbulence ◽  
Tollmien Schlichting

The natural and bypass routes to boundary-layer turbulence have traditionally been studied independently. In certain flow regimes, both transition mechanisms might coexist, and, if so, can interact. A nonlinear interaction of discrete and continuous Orr-Sommerfeld modes, which are at the origin of orderly and bypass transition, respectively, is found. It causes breakdown to turbulence, even though neither mode alone is sufficient. Direct numerical simulations of the interaction shows that breakdown occurs through a pattern of Λ-structures, similar to the secondary instability of Tollmien–Schlichting waves. However, the streaks produced by the Orr-Sommerfeld continuous mode set the spanwise length scale, which is much smaller than that of the secondary instability of Tollmien–Schlichting waves. Floquet analysis explains some of the features seen in the simulations as a competition between destabilizing and stabilizing interactions between finite-amplitude distortions.

Bypass Transition Modelling: A New Method Which Accounts for Free-Stream Turbulence Intensity and Length Scale

2000 ◽  
Author(s):  
Paul E. Roach ◽  
David H. Brierley
Keyword(s):  
Boundary Layer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Test Surface ◽  
Length Scale ◽  
Pressure Gradients ◽  
Layer Transition ◽  
Free Stream Turbulence

The publication of the present authors’ boundary layer transition data in 1992 (now widely known as the ERCOFTAC test case T3) has led to a spate of new experimental and modelling efforts aimed at improving our understanding of this problem. This paper describes a new method of determining boundary layer transition with zero mean pressure gradient. The approach examines the development of a laminar boundary layer to the start of transition, accounting for the influences of free-stream turbulence and test surface geometry. It is presented as a “proof of concept”, requiring a significant amount of work before it can be considered as a practically applicable model for transition prediction. The method is based upon one first put forward by G.I. Taylor in the 1930’s, and accounts for the action of local, instantaneous pressure gradients on the developing laminar boundary layer. These pressure gradients are related to the intensity and length scale of turbulence in the free-stream using Taylor’s simple isotropic model. The findings demonstrate the need to account for the separate influences of free-stream turbulence intensity and length scale when considering the transition process. Although the length scale has less of an effect than the intensity, its influence is, nevertheless, significant and must not be overlooked. This fact goes a long way towards explaining the large scatter to be found in simple correlations which involve only the turbulence intensity. Intriguingly, it is demonstrated that it is the free-stream turbulence at the leading edge of the test surface which is important, not that found locally outside the boundary layer. The additional influence of leading edge geometry is also shown to play a major role in fixing the point at which transition begins. It is suggested that the leading edge geometry will distort the incident turbulent eddies, modifying the effective “free-stream” turbulence properties. Consequently, it is shown that the scale of the eddies relative to the leading edge thickness is a further important parameter, and helps bring together a large number of test cases.

EXPERIMENTAL AND NUMERICAL INVESTIGATIONS OF BOUNDARY LAYER TRANSITION ON BLUNTED CONES AT SUPERSONIC FLOW

2010 ◽  
Vol 40 (3) ◽  
pp. 309-319 ◽  
Author(s):  
V. N. Brazhko ◽  
A. V. Vaganov ◽  
N. A. Kovaleva ◽  
N. P. Kolina ◽  
I. I. Lipatov
Keyword(s):  
Boundary Layer ◽  
Supersonic Flow ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Numerical Investigations

Automatic control of laminar boundary-layer transition

AIAA Journal ◽  
1997 ◽  
Vol 35 ◽  
pp. 85-90
Author(s):  
P. A. Nelson ◽  
M. C. M. Wright ◽  
J.-L. Rioual
Keyword(s):  
Boundary Layer ◽  
Automatic Control ◽  
Laminar Boundary Layer ◽  
Boundary Layer Transition ◽  
Layer Transition
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