The Role of Large-Scale Motions in the Separation Process of a Turbulent Boundary Layer on a Curved Surface

1983 ◽  
pp. 65-66
Author(s):  
Qing-Ding Wei ◽  
Hiroshi Sato
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Separation Process ◽  
Curved Surface

On the role of the outer region in the turbulent-boundary-layer bursting process

1994 ◽  
Vol 259 ◽  
pp. 345-373 ◽  
Author(s):  
ROY Y. Myose ◽  
Ron F. Blackwelder
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Outer Region ◽  
Low Speed ◽  
Moderate Reynolds Number ◽  
Eddy Structures ◽  
Low Speed Streaks ◽  
Bursting Process

The dynamics and interaction of turbulent-boundary-layer eddy structures was experimentally emulated. Counter-rotating streamwise vortices and low-speed streaks emulating turbulent-boundary-layer wall eddies were generated by a Görtler instability mechanism. Large-scale motions associated with the outer region of turbulent boundary layer were emulated with — ωzspanwise vortical eddies shed by a periodic non-sinusoidal oscillation of an airfoil. The scales of the resulting eddy structures were comparable to a moderate-Reynolds-number turbulent boundary layer. Results show that the emulated wall-eddy breakdown was triggered by streamwise acceleration associated with the outer region of turbulent boundary layer. This breakdown involved violent mixing between low-speed fluid from the wall eddy and accelerated fluid associated with the outer structure. Although wall eddies can break down autonomously, the presence of and interaction with outer-region — ωzeddies hastened their breakdown. Increasing the — ωzeddy strength resulted in further hastening of the breakdown. Conversely, + ωzeddies were found to delay wall-eddy breakdown locally, with further delays resulting from stronger + ωzeddies. This suggests that the outer region of turbulent boundary layers plays a role in the bursting process.

Large-scale motion in the intermittent region of a turbulent boundary layer

1970 ◽  
Vol 41 (2) ◽  
pp. 283-325 ◽  
Author(s):  
Leslie S. G. Kovasznay ◽  
Valdis Kibens ◽  
Ron F. Blackwelder
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Cross Correlation ◽  
Turbulent Regime ◽  
Conditional Sampling ◽  
Correlation Data ◽  
Measuring Techniques ◽  
Conditional Averaging ◽  
Scale Motion

The outer intermittent region of a fully developed turbulent boundary layer with zero pressure gradient was extensively explored in the hope of shedding some light on the shape and motion of the interface separating the turbulent and non-turbulent regions as well as on the nature of the related large-scale eddies within the turbulent regime. Novel measuring techniques were devised, such as conditional sampling and conditional averaging, and others were turned to new uses, such as reorganizing in map form the space-time auto- and cross-correlation data involving both the U and V velocity components as well as I, the intermittency function. On the basis of the new experimental results, a conceptual model for the development of the interface and for the entrainment of new fluid is proposed.

Resonant flow in small cavities submerged in a boundary layer

1988 ◽  
Vol 420 (1859) ◽  
pp. 219-245 ◽  
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Resonant Cavity ◽  
Cavity Flow ◽  
Flow Speed ◽  
Small Scale ◽  
S Waves ◽  
Grooved Surface ◽  
Tollmien Schlichting

The viscosity-dominated unsteady flow in a row of small transverse square cavities lying submerged in a turbulent boundary layer is first considered. Experiments performed primarily with one size of cavities show that the cavity flow can be excited by freestream disturbances in a narrow frequency band that is independent of the flow speed. The turbulent boundary layer in which the cavities are submerged remains transparent to the disturbances. The cavity flow resonates when the depths of the cavity and the Stokes layer are nearly the same, that is when 2π fk 2 / v = 1, where f is the frequency of the resonant cavity flow, k is the cavity height and v is the kinematic viscosity of the fluid. An associated laminar boundary-layer excitation experiment shows that the instability process over the grooved surface also involves the amplification of Tollmien–Schlichting (T–S) waves in much the same manner as in a smooth-wall Blasius profile but the grooves enhance receptivity. A theory is given proposing that the resonant groove flow in the low Reynolds number turbulent boundary layer is driven by highly amplified matched T–S waves. The possible relevance of the observed coupling between the large-scale freestream disturbances and the small-scale cavity flows to the turbulence production mechanism in a smooth flat-plate turbulent boundary layer is also discussed.

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