On the stability of a Blasius boundary layer subject to localised suction

2019 ◽  
Vol 871 ◽  
pp. 717-741 ◽  
Author(s):  
Mattias Brynjell-Rahkola ◽  
Ardeshir Hanifi ◽  
Dan S. Henningson
Keyword(s):  
Boundary Layer ◽  
Flow Instability ◽  
Linear Instability ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Layer Transition ◽  
Structural Sensitivity ◽  
Blasius Boundary Layer ◽  
Structural Sensitivity Analysis ◽  
The Stability

In this study the origins of premature transition due to oversuction in boundary layers are studied. An infinite row of circular suction pipes that are mounted at right angles to a flat plate subject to a Blasius boundary layer is considered. The interaction between the flow originating from neighbouring holes is weak and for the parameters investigated, the pipe is always found to be unsteady regardless of the state of the flow in the boundary layer. A stability analysis reveals that the appearance of boundary layer transition can be associated with a linear instability in the form of two unstable eigenmodes inside the pipe that have weak tails, which extend into the boundary layer. Through an energy budget and a structural sensitivity analysis, the origin of this flow instability is traced to the structures developing inside the pipe near the pipe junction. Although the amplitudes of the modes in the boundary layer are orders of magnitude smaller than the corresponding amplitudes inside the pipe, a Koopman analysis of the data gathered from a nonlinear direct numerical simulation confirms that it is precisely these disturbances that are responsible for transition to turbulence in the boundary layer due to oversuction.

scholarly journals Edge tracking in spatially developing boundary layer flows

2019 ◽  
Vol 881 ◽  
pp. 164-181 ◽  
Author(s):  
Miguel Beneitez ◽  
Yohann Duguet ◽  
Philipp Schlatter ◽  
Dan S. Henningson
Keyword(s):  
Boundary Layer ◽  
Basins Of Attraction ◽  
Base Flow ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Structure Characteristic ◽  
Asymptotic State ◽  
Bypass Transition ◽  
Layer Transition ◽  
Blasius Boundary Layer

Recent progress in understanding subcritical transition to turbulence is based on the concept of the edge, the manifold separating the basins of attraction of the laminar and the turbulent state. Originally developed in numerical studies of parallel shear flows with a linearly stable base flow, this concept is adapted here to the case of a spatially developing Blasius boundary layer. Longer time horizons fundamentally change the nature of the problem due to the loss of stability of the base flow due to Tollmien–Schlichting (TS) waves. We demonstrate, using a moving box technique, that efficient long-time tracking of edge trajectories is possible for the parameter range relevant to bypass transition, even if the asymptotic state itself remains out of reach. The flow along the edge trajectory features streak switching observed for the first time in the Blasius boundary layer. At long enough times, TS waves co-exist with the coherent structure characteristic of edge trajectories. In this situation we suggest a reinterpretation of the edge as a manifold dividing the state space between the two main types of boundary layer transition, i.e. bypass transition and classical transition.

Boundary Layer Transition at High Levels of Free Stream Turbulence

1998 ◽  
Author(s):  
Masaharu Matsubara ◽  
P. Henrik Alfredsson ◽  
K. Johan A. Westin
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Turbine Blades ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Flow Visualisation ◽  
Mean Flow ◽  
Layer Transition ◽  
Free Stream Turbulence

Transition to turbulence in laminar boundary layers subjected to high levels of free stream turbulence (FST) can still not be reliably predicted, despite its technical importance, e.g. in the case of boundary layers developing on gas turbine blades. In a series of experiments in the MTL-wind tunnel at KTH the influence of grid-generated FST on boundary layer transition has been studied, with FST-levels up to 6%. It was shown from both flow visualisation and hot-wire measurements that the boundary layer develops unsteady streaky structures with high and low streamwise velocity. This leads to large amplitude low frequency fluctuations inside the boundary layer although the mean flow is still close to the laminar profile. Breakdown to turbulence occurs through an instability of the streaks which leads to the formation of turbulent spots. Accurate physical modelling of these processes seems to be needed in order to obtain a reliable prediction method.

Effect of Nozzle Shape and Polymer Additives on Water Jet Appearance

1979 ◽  
Vol 101 (3) ◽  
pp. 304-308 ◽  
Author(s):  
J. W. Hoyt ◽  
J. J. Taylor
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Water Jet ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Polymer Additives ◽  
High Speed Photography ◽  
Layer Transition ◽  
Spray Formation ◽  
Exit Surface

The effects of shape parameters on the performance of water-jet nozzles discharging in air were investigated using a camera specially adapted for jet photography. The boundary-layer developing on the exit surface of the nozzle is shown to account for the jet appearance revealed by high speed photography. Optimum nozzles seem to have the boundary-layer transition to turbulence inside the nozzle; transition outside the nozzle being accompanied by spray formation and early jet disruption. The effect of polymer additives seems to be earlier transition and a thinner turbulent boundary layer inside the nozzle which improves jet performance.

Application of Constructal Theory to Prediction of Boundary Layer Transition Onset

2006 ◽  
Author(s):  
E. J. Walsh ◽  
D. H. Hernon ◽  
D. M. McEligot ◽  
M. R. D. Davies ◽  
A. Bejan
Keyword(s):  
Boundary Layer ◽  
Transition Process ◽  
Boundary Layer Transition ◽  
Constructal Theory ◽  
Transition To Turbulence ◽  
Bypass Transition ◽  
Layer Transition ◽  
New Approach ◽  
Transition Modeling ◽  
New Perspective

Accurate transition onset modeling is a fundamental part of modern turbomachinery designs, where bypass transition is the dominant mechanism of transition to turbulence. Despite this situation a range of transition onset models exist primarily based upon both integral and local parameters within the boundary layer. All such transition models have empirical origins. To date the relationships between such models has not been forthcoming and hence lack of physical understanding of the transition process is evident. This paper details a new approach to transition modeling and provides a theoretically based approach to transition onset prediction by invoking a single principle developed within constructal theory. We not only present a new model but also demonstrate the equivalence between existing models by implementing the same theory. Such understanding of the transition onset problem may provide a new perspective towards more theoretically based transition onset models rather than empirical ones, although much work remains to be done in understanding the receptivity mechanisms within a laminar boundary layer.

The resonant-triad nonlinear interaction in boundary-layer transition

1987 ◽  
Vol 179 ◽  
pp. 227-252 ◽  
Author(s):  
F. T. Smith ◽  
P. A. Stewart
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Quantitative Agreement ◽  
Finite Amplitude ◽  
Boundary Layer Transition ◽  
Transition To Turbulence ◽  
Layer Transition ◽  
Structured Analysis

Recent controlled experiments by Kachanov & Levchenko (1984) and others indicate that, during some slower kinds of transition to turbulence in boundary layers, three-dimensionality can come into play initially as a resonant-triad phenomenon, depending on the disturbance sizes present. The triad interaction, suggested theoretically in the boundary-layer context by Craik (1971) and others, is studied in the present work by means of multi-structured analysis for high characteristic Reynolds numbers. A finite-amplitude/relatively high-frequency approach leads rationally to the nonlinear triad equations, solutions for which are then obtained analytically and computationally in certain central cases of interest (temporal and spatial). The solutions have a rather chaotic spiky appearance as continual energy exchange develops between the two- and three-dimensional nonlinear modes, whose large-scale response seems governed by inviscid dynamics but subject to important, continual ‘rejuvenation’ from small- (fast-) scale viscous action in-between. The three-dimensional growth rate is thereby increased, but not the two-dimensional. Subsequently the disturbed flow enters a higher-amplitude regime similar to that studied in some related papers by the authors and co-workers. Comparisons with the experiments are very supportive of the theory (in the small and in the large), yielding both qualitative and quantitative agreement.

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