On subcritical breakdown to turbulence in swept wing attachment line boundary layer flows

1997 ◽  
pp. 351-358 ◽  
Author(s):  
V. Theofilis ◽  
U. Dallmann
Keyword(s):  
Boundary Layer ◽  
Swept Wing ◽  
Boundary Layer Flows ◽  
Attachment Line

Investigation of Formation and Development of Stationary and Secondary Disturbances in the Favourable Pressure Gradient Area on the Swept Wing

2013 ◽  
Vol 8 (2) ◽  
pp. 55-69
Author(s):  
Stepan Tolkachev ◽  
Vasily Gorev ◽  
Viktor Kozlov
Keyword(s):  
Boundary Layer ◽  
Roughness Element ◽  
Swept Wing ◽  
Liquid Crystal Thermography ◽  
Natural Case ◽  
Turbulent Transition ◽  
Stage Transition ◽  
The Moment ◽  
Combined Technique ◽  
Attachment Line

In this work the combined technique of liquid-crystal thermography and thermoanemometry measurements is used to trace the stationary disturbance development from the moment of formation to the nonlinear stage transition. It has been shown that the pair of stationary vortices are formed after the cylindrical roughness element. These vortices modify a boundary layer and destabilize it. There is the area of maximal receptivity to the roughness location, which in the experiment was distant from the attachment line. If the stationary disturbance has enough magnitude in its core the secondary disturbances excite and lead to the laminar-turbulent transition. Secondary disturbances are sensitive to the acoustics and achieve the magnitude in hundred times higher than for the natural case

The Calculation of Three-Dimensional Turbulent Boundary Layers: Part II: Attachment-Line Flow on an Infinite Swept Wing

1967 ◽  
Vol 18 (2) ◽  
pp. 150-164 ◽  
Author(s):  
N. A. Cumpsty ◽  
M. R. Head
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Flow ◽  
Three Dimensional ◽  
Cross Flow ◽  
Swept Wing ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow ◽  
Momentum Integral ◽  
Attachment Line

SummaryAn earlier paper described a method of calculating the turbulent boundary layer flow over the rear of an infinite swept wing. It made use of an entrainment equation and momentum integral equations in streamwise and cross-flow directions, together with several auxiliary assumptions. Here the method is adapted to the calculation of the turbulent boundary layer flow along the attachment line of an infinite swept wing. In this case the cross-flow momentum integral equation reduces to the identity 0 = 0 and must be replaced by its differentiated form. Two alternative approaches are also adopted and give very similar results, in good agreement with the limited experimental data available. It is found that results can be expressed as functions of a single parameter C*, which is evidently the criterion of similarity for attachment-line flows.

Receptivity and sensitivity of the leading-edge boundary layer of a swept wing

2015 ◽  
Vol 775 ◽  
Author(s):  
Gianluca Meneghello ◽  
Peter J. Schmid ◽  
Patrick Huerre
Keyword(s):  
Boundary Layer ◽  
Flow Instability ◽  
Cross Flow ◽  
Leading Edge ◽  
Open Loop ◽  
Base Flow ◽  
Local Instability ◽  
Swept Wing ◽  
Global Mode ◽  
Attachment Line

A global stability analysis of the boundary layer in the leading edge of a swept wing is performed in the incompressible flow regime. It is demonstrated that the global eigenfunctions display the features characterizing the local instability of the attachment line, as in swept Hiemenz flow, and those of local cross-flow instabilities further downstream along the wing. A continuous connection along the chordwise direction is established between the two local eigenfunctions. An adjoint-based receptivity analysis reveals that the global eigenfunction is most responsive to forcing applied in the immediate vicinity of the attachment line. Furthermore, a sensitivity analysis identifies the wavemaker at a location that is also very close to the attachment line where the corresponding local instability analysis holds: the local cross-flow instability further along the wing is merely fed by its attachment-line counterpart. As a consequence, global mode calculations for the entire leading-edge region only need to include attachment-line structures. The result additionally implies that effective open-loop control strategies should focus on base-flow modifications in the region where the local attachment-line instability prevails.

Experimental Techniques of the Study of the Vortex Disturbances Structure Caused by Point Injection on the Swept Wing Leading Edge

2012 ◽  
Vol 7 (2) ◽  
pp. 66-79
Author(s):  
Stepan Tolkachev ◽  
Vasily Gorev ◽  
Galina Zharkova ◽  
Valentina Kovrizhina
Keyword(s):  
Boundary Layer ◽  
Liquid Crystal ◽  
Leading Edge ◽  
Swept Wing ◽  
Liquid Crystal Thermography ◽  
Point Injection ◽  
Stationary Vortex ◽  
To Receive ◽  
Attachment Line ◽  
Good Agreement

The article contains the results of thermoanemometry on the curvilinear surface and liquid crystal thermography techniques for the investigation of the flow stability on the swept wing leading edge. The numeric results of the velocity disturbance distribution in the boundary layer near the attachment line were received with a help of the thermoanemometry technique. It was found out, that the boundary layer become less stable, when a stationary vortex modifies the flow. The liquid crystal thermography technique allowed to expand the workspace for investigations up to 70 from the attachment line, to receive the visualization pictures of disturbed flow for several regimes of blowing, to reveal an influence of the blow velocity on dimensions and trajectory of stationary disturbances, which were induced by injection. The results of visualizations are in a good agreement with thermoanemometry results

scholarly journals Algebraically decaying modes and wave packet pseudo-modes in swept Hiemenz flow

2009 ◽  
Vol 643 ◽  
pp. 309-332 ◽  
Author(s):  
DOMINIK OBRIST ◽  
PETER J. SCHMID
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Free Stream ◽  
Travelling Wave ◽  
Swept Wing ◽  
Algebraic Decay ◽  
Infinite Domains ◽  
The Family ◽  
Hiemenz Flow ◽  
Attachment Line

The modal structure of the swept Hiemenz flow, a model for the flow near the attachment line of a swept wing, consists of eigenfunctions which exhibit (super-)exponential or algebraic decay as the wall-normal coordinate tends to infinity. The subset of algebraically decaying modes corresponds to parts of the spectrum which are characterized by a significant sensitivity to numerical discretization. Numerical evidence further suggests that a continuous spectrum covering a two-dimensional range of the complex plane exists. We investigate the family of uniform swept Hiemenz modes using eigenvalue computations, numerical simulations and the concept of wave packet pseudo-modes. Three distinct branches of the family of algebraically decaying eigenmodes are identified. They can be superimposed to produce wavefronts propagating towards or away from the boundary layer and standing or travelling wave packets in the free stream. Their role in the exchange of information between the free stream and the attachment-line boundary layer for the swept Hiemenz flow is discussed. The concept of wave packet pseudo-modes has been critical in the analysis of this problem and is expected to lead to further insights into other shear flows in semi- or bi-infinite domains.

The Calculation of the Three-Dimensional Turbulent Boundary Layer: Part III. Comparison of Attachment-Line Calculations with Experiment

1969 ◽  
Vol 20 (2) ◽  
pp. 99-113 ◽  
Author(s):  
N. A. Cumpsty ◽  
M. R. Head
Keyword(s):  
Boundary Layer ◽  
Full Range ◽  
Three Dimensional ◽  
Velocity Profiles ◽  
Transition Regime ◽  
Swept Wing ◽  
Nose Radius ◽  
Measured Velocity ◽  
Wide Range ◽  
Attachment Line

SummaryWind tunnel measurements have been made of the attachment-line boundary layer on a swept wing. The combination of a 4-5 in (114 mm) nose radius and 60° angle of sweep enabled a wide range of values of the parameter V2/(v dU/dx) (denoted here by C*), to be covered, and gave a thick enough boundary layer for the velocity profiles to be accurately measured. Pitot traverses were performed for values of C* from 0·59 × 105 to 3·7 × 105. Without a trip wire fitted the attachment-line flow was laminar over the full range and the measured velocity profiles agreed closely with the theory for an infinite swept wing. With a large trip wire fitted, a transition régime was observed in the range 0·6 × 105 < C* < 1·4 × 105, and at higher values of C* the flow was fully turbulent and showed good agreement with the earlier calculations of Cumpsty and Head. Preston tubes were used for skin friction measurements in fully turbulent conditions and a hot wire was used to explore the development of turbulence in the transition régime.

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