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.

Triadic scale interactions in a turbulent boundary layer

2015 ◽  
Vol 767 ◽  
Author(s):  
Subrahmanyam Duvvuri ◽  
Beverley J. McKeon
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Small Scale ◽  
Velocity Signal ◽  
Small Scales ◽  
Amplitude Modulation Coefficient ◽  
Scale Turbulence ◽  
Scale Motion ◽  
Phase Relationships

AbstractA formal relationship between the skewness and the correlation coefficient of large and small scales, termed the amplitude modulation coefficient, is established for a general statistically stationary signal and is analysed in the context of a turbulent velocity signal. Both the quantities are seen to be measures of phase in triadically consistent interactions between scales of turbulence. The naturally existing phase relationships between large and small scales in a turbulent boundary layer are then manipulated by exciting a synthetic large-scale motion in the flow using a spatially impulsive dynamic wall roughness perturbation. The synthetic scale is seen to alter the phase relationships, or the degree of modulation, in a quasi-deterministic manner by exhibiting a phase-organizing influence on the small scales. The results presented provide encouragement for the development of a practical framework for favourable manipulation of energetic small-scale turbulence through large-scale inputs in a wall-bounded turbulent flow.

scholarly journals Correlation between Large-Scale Streamwise Velocity Features and the Height of Coherent Vortices in a Turbulent Boundary Layer

Fluids ◽  
2021 ◽  
Vol 6 (8) ◽  
pp. 286
Author(s):  
Shaurya Shrivastava ◽  
Theresa Saxton-Fox
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Streamwise Velocity ◽  
Wake Region ◽  
Strong Negative Correlation ◽  
Vortex Model ◽  
Image Velocimetry ◽  
Coherent Vortices ◽  
Conditional Averaging

The preferential organisation of coherent vortices in a turbulent boundary layer in relation to local large-scale streamwise velocity features was investigated. Coherent vortices were identified in the wake region using the Triple Decomposition Method (originally proposed by Kolář) from 2D particle image velocimetry (PIV) data of a canonical turbulent boundary layer. Two different approaches, based on conditional averaging and quantitative statistical analysis, were used to analyze the data. The large-scale streamwise velocity field was first conditionally averaged on the height of the detected coherent vortices and a change in the sign of the average large scale streamwise fluctuating velocity was seen depending on the height of the vortex core. A correlation coefficient was then defined to quantify this relationship between the height of coherent vortices and local large-scale streamwise fluctuating velocity. Both of these results indicated a strong negative correlation in the wake region of the boundary layer between vortex height and large-scale velocity. The relationship between vortex height and full large-scale velocity isocontours was also studied and a conceptual model based on the findings of the study was proposed. The results served to relate the hairpin vortex model of Adrian et al. to the scale interaction results reported by Mathis et al., and Chung and McKeon.

On the wall structure of the turbulent boundary layer

1976 ◽  
Vol 76 (1) ◽  
pp. 89-112 ◽  
Author(s):  
R. F. Blackwelder ◽  
R. E. Kaplan
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Reynolds Shear Stress ◽  
Streamwise Velocity ◽  
Mean Value ◽  
Wall Structure ◽  
Spanwise Direction ◽  
Normal Velocity ◽  
Conditional Sampling

The wall structure of the turbulent boundary layer was examined using hot-wire rakes and conditional sampling techniques. Instantaneous velocity measurements indicate a high degree of coherence over a considerable area in the direction normal to the wall. Aty+= 15, there is some evidence of large-scale correlation in the spanwise direction, but almost no indication of the streamwise streaks that exist in the lower regions of the boundary layer. Conditional sampling showed that the normal velocity is directed outwards in regions of strong stream-wise-momentum deficit, and inwards when the streamwise velocity exceeds its mean value. The conditionally averaged Reynolds shear stress was approximately an order of magnitude greater than its conventionally averaged value and decayed slowly downstream.

Large-scale motion in a turbulent boundary layer: a study using temperature contamination

1978 ◽  
Vol 89 (1) ◽  
pp. 1-31 ◽  
Author(s):  
Chyan-Hai P. Chen ◽  
Ron F. Blackwelder
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Shear Layer ◽  
Large Scale ◽  
Internal Temperature ◽  
Temperature Front ◽  
Large Structures ◽  
Entire Boundary ◽  
Logarithmic Region ◽  
Scale Motion

A fully developed turbulent boundary layer with a zero pressure gradient was explored by using temperature as a passive contaminant in order to study the large-scale structure. The temperature tracer was introduced into the flow field by heating the entire wall to approximately 12°C above the free-stream temperature. The most interesting observation was the existence of a sharp internal temperature front, characterized by a rapid decrease in temperature, that extended throughout the entire boundary layer. In the outer, intermittent region, the internal temperature front was always associated with the upstream side of the turbulent bulges, i.e. the ‘backs’. It extended across the entire logarithmic region and was related to the sharp acceleration associated with the bursting phenomenon near the wall. Conditional averages of the velocities measured with the temperature front revealed that it was associated with an internal shear layer. The results suggest that this shear layer provides a dynamical relationship between the large structures in the outer, intermittent region and the bursting phenomenon near the wall.

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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