The effect of the shear layer between large scale motions on bursting phenomenon in turbulent boundary layer

2020 ◽  
Vol 2020 (0) ◽  
pp. OS02-02
Author(s):  
Xiaonan CHEN ◽  
Koji IWANO ◽  
Yasuhiko SAKAI ◽  
Yasumasa ITO
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Shear Layer ◽  
Large Scale

Mechanisms of Turbulence Transport in a Turbine Blade Coolant Passage With a Rib Turbulator

1999 ◽  
Vol 121 (1) ◽  
pp. 152-159 ◽  
Author(s):  
P. K. Panigrahi ◽  
S. Acharya
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Turbulent Boundary Layer ◽  
Shear Layer ◽  
Large Scale ◽  
Turbulence Models ◽  
Turbulent Shear ◽  
Large Scale Structures ◽  
Turbulent Shear Stress ◽  
Scale Structures

This paper provides detailed measurements of the flow in a ribbed coolant passage, and attempts to delineate the important mechanisms that contribute to the production of turbulent shear stress and the normal stresses. It is shown that the separated flow behind the rib is dictated by large-scale structures, and that the dynamics of the large-scale structures, associated with sweep, ejection, and inward and outward interactions, all play an important role in the production of the turbulent shear stress. Unlike the turbulent boundary layer, in a separated shear flow past the rib, the inward and outward interaction terms are both important, accounting for a negative stress production that is nearly half of the positive stress produced by the ejection and sweep mechanisms. It is further shown that the shear layer wake persists well past the re-attachment location of the shear layer, implying that the flow between ribbed passages never recovers to that of a turbulent boundary layer. Therefore, even past re-attachment, the use of statistical turbulence models that ignore coherent structure dynamics is inappropriate.

Transition Mechanisms in Separation Bubbles Under Low and Elevated Freestream Turbulence

2007 ◽  
Author(s):  
B. R. McAuliffe ◽  
M. I. Yaras
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Numerical Simulations ◽  
Shear Layer ◽  
Laminar Boundary Layer ◽  
Large Scale ◽  
Freestream Turbulence ◽  
Turbulent Spots ◽  
Separated Shear Layer ◽  
Separation Bubbles

Through numerical simulations, this paper examines the nature of instability mechanisms leading to transition in separation bubbles. The results of two direct numerical simulations are presented in which separation of a laminar boundary layer occurs over a flat surface in the presence of an adverse pressure gradient. The primary difference in the flow conditions between the two simulations is the level of freestream turbulence with intensities of 0.1% and 1.45% at separation. In the first part of the paper, transition under a low-disturbance environment is examined, and the development of the Kelvin-Helmholtz instability in the separated shear layer is compared to the well-established instability characteristics of free shear layers. The study examines the role of the velocity-profile shape on the instability characteristics and the nature of the large-scale vortical structures shed downstream of the bubble. The second part of the paper examines transition in a high-disturbance environment, where the above-mentioned mechanism is bypassed as a result of elevated freestream turbulence. Filtering of the freestream turbulence into the laminar boundary layer results in streamwise streaks which provide conditions under which turbulent spots are produced in the separated shear layer, grow, and then merge to form a turbulent boundary layer. The results allow identification of the structure of the instability mechanism and the characteristic structure of the resultant turbulent spots. Recovery of the reattached turbulent boundary layer is then examined for both cases. The large-scale flow structures associated with transition are noted to remain coherent far downstream of reattachment, delaying recovery of the turbulent boundary layer to an equilibrium state.

Transition Mechanisms in Separation Bubbles Under Low- and Elevated-Freestream Turbulence

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Brian R. McAuliffe ◽  
Metin I. Yaras
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Numerical Simulations ◽  
Shear Layer ◽  
Laminar Boundary Layer ◽  
Large Scale ◽  
Freestream Turbulence ◽  
Turbulent Spots ◽  
Separated Shear Layer ◽  
Separation Bubbles

Through numerical simulations, this paper examines the nature of instability mechanisms leading to transition in separation bubbles. The results of two direct numerical simulations are presented in which separation of a laminar boundary layer occurs over a flat surface in the presence of an adverse pressure gradient. The primary difference in the flow conditions between the two simulations is the level of freestream turbulence with intensities of 0.1% and 1.45% at separation. In the first part of the paper, transition under a low-disturbance environment is examined, and the development of the Kelvin–Helmholtz instability in the separated shear layer is compared to the well-established instability characteristics of free shear layers. The study examines the role of the velocity-profile shape on the instability characteristics and the nature of the large-scale vortical structures shed downstream of the bubble. The second part of the paper examines transition in a high-disturbance environment, where the above-mentioned mechanism is bypassed as a result of elevated-freestream turbulence. Filtering of the freestream turbulence into the laminar boundary layer results in streamwise streaks, which provide conditions under which turbulent spots are produced in the separated shear layer, grow, and then merge to form a turbulent boundary layer. The results allow identification of the structure of the instability mechanism and the characteristic structure of the resultant turbulent spots. Recovery of the reattached turbulent boundary layer is then examined for both cases. The large-scale flow structures associated with transition are noted to remain coherent far downstream of reattachment, delaying recovery of the turbulent boundary layer to an equilibrium state.

scholarly journals Mechanisms of Turbulence Transport in a Turbine Blade Coolant Passage With a Rib-Turbulator

1997 ◽  
Author(s):  
P. K. Panigrahi ◽  
S. Acharya
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Turbulent Boundary Layer ◽  
Shear Layer ◽  
Large Scale ◽  
Turbulence Models ◽  
Turbulent Shear ◽  
Large Scale Structures ◽  
Turbulent Shear Stress ◽  
Scale Structures

This paper provides detailed measurements of the flow in a ribbed coolant passage, and attempts to delineate the important mechanisms that contribute to the production of turbulent shear stress and the normal stresses. It is shown that the separated flow behind the rib is dictated by large scale structures, and that the dynamics of the large scale structures, associated with sweep, ejection, and inward and outward interactions all play an important role in the production of the turbulent shear stress. Unlike the turbulent boundary layer, in a separated shear flow past the rib, the inward and outward interaction terms are both important accounting for a negative stress production that is nearly half of the positive stress produced by the ejection and sweep mechanisms. It is further shown, that the shear layer wake persists well past the re-attachment location of the shear layer, implying that the flow between ribbed passages never recovers to that of a turbulent boundary layer. Therefore, even past re-attachment, the use of statistical turbulence models that ignore coherent structure dynamics is inappropriate.

Ordered motion in the turbulent boundary layer over wind waves

1988 ◽  
Vol 197 ◽  
pp. 105-138 ◽  
Author(s):  
H. Kawamura ◽  
Y. Toba
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Shear Layer ◽  
Large Scale ◽  
Separation Bubble ◽  
Wind Waves ◽  
Outer Boundary ◽  
High Shear ◽  
Air Mass ◽  
Bursting Phenomena

The turbulent boundary layer over young wind waves (C/u* ∼ 1, where C is the phase speed of wind waves and u* is the friction velocity) has been investigated in a laboratory tank. Ordered motions have been found, and their structures studied in detail. Visualization of the outer boundary layer (0.4δ–1δ, where δ is the boundary-layer thickness) by paraffin mist has demonstrated the existence of a train of large-scale ordered motions having a horizontal lengthscale that corresponds to the wavelength of the underlying wind waves. Hot-wire measurements combined with the visualization have shown that the passage of the outer boundary-layer bulge is related to the occurrence of a low-speed air mass, usually accompanied by an upward velocity to produce large Reynolds stress. In the vicinity of the wave surface (0–0.15δ), flow separation occurs over these wind waves. Instantaneous velocity shear measurements, using two hot wires 0.15 cm apart vertically, have detected a high-shear layer at the edge of the separation bubbles. This high-shear layer, the potential site for generating much turbulence, reattaches on the windward side of the preceding wind waves. A pressure rise and a shear-stress spike, expected near the reattachment region, could be the mechanisms for supplying energy to the wind waves.The bursting phenomena over wind waves have been examined in detail in the logarithmic boundary layer (0.15δ–0.3δ). The bursting phenomena are a major mechanism for producing Reynolds stress and have a specific relationship with the phase of the wind wave. To explain the bursting phenomena, two mechanisms (not present in the boundary layer over a flat plate) are proposed, involving air-flow separation and the large-scale ordered motions, respectively. The two mechanisms are a ‘big burst’ related to the discharge of a whole separation bubble, and a ‘small burst’ which is the upward bursting of a low-speed air mass from the unstable separated shear layer into the ordered motions passing over a separation bubble.

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.

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.

The structure of a highly decelerated axisymmetric turbulent boundary layer

2021 ◽  
Vol 929 ◽  
Author(s):  
N. Agastya Balantrapu ◽  
Christopher Hickling ◽  
W. Nathan Alexander ◽  
William Devenport
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Shear Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Large Scale ◽  
Convection Velocity ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean

Experiments were performed over a body of revolution at a length-based Reynolds number of 1.9 million. While the lateral curvature parameters are moderate ( $\delta /r_s < 2, r_s^+>500$ , where $\delta$ is the boundary layer thickness and r s is the radius of curvature), the pressure gradient is increasingly adverse ( $\beta _{C} \in [5 \text {--} 18]$ where $\beta_{C}$ is Clauser’s pressure gradient parameter), representative of vehicle-relevant conditions. The mean flow in the outer regions of this fully attached boundary layer displays some properties of a free-shear layer, with the mean-velocity and turbulence intensity profiles attaining self-similarity with the ‘embedded shear layer’ scaling (Schatzman & Thomas, J. Fluid Mech., vol. 815, 2017, pp. 592–642). Spectral analysis of the streamwise turbulence revealed that, as the mean flow decelerates, the large-scale motions energize across the boundary layer, growing proportionally with the boundary layer thickness. When scaled with the shear layer parameters, the distribution of the energy in the low-frequency region is approximately self-similar, emphasizing the role of the embedded shear layer in the large-scale motions. The correlation structure of the boundary layer is discussed at length to supply information towards the development of turbulence and aeroacoustic models. One major finding is that the estimation of integral turbulence length scales from single-point measurements, via Taylor's hypothesis, requires significant corrections to the convection velocity in the inner 50 % of the boundary layer. The apparent convection velocity (estimated from the ratio of integral length scale to the time scale), is approximately 40 % greater than the local mean velocity, suggesting the turbulence is convected much faster than previously thought. Closer to the wall even higher corrections are required.

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