A coherent structure model of the turbulent boundary layer and its ability to predict Reynolds number dependence

1991 ◽  
Vol 336 (1641) ◽  
pp. 103-129 ◽  
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Reynolds Stress ◽  
Coherent Structure ◽  
Large Scale ◽  
Outer Region ◽  
Structure Model ◽  
Hairpin Vortices ◽  
Reynolds Number Dependence

The coherent motions identified in passively marked turbulent boundary-layer experiments are reviewed. Data obtained in our laboratory using simultaneous hot-wire anemometry and flow visualization are analysed to provide measures of the percent contribution of the coherent motions to the total Reynolds stress. A coherent structure model is then developed. In the outer region the model incorporates the large-scale motions, the typical eddies and their interactions. In the wall region the model is characterized by the long streaks, their associated hairpin vortices, and the pockets with their associated pocket and hairpin vortices. The motions in both regions have unique phase relations which play an important role in their evolution and the resulting intensity of their interactions. In addition, the inner-outer region interactions are seen to be strong because typical eddies, microscale motions which can directly initiate the bursting process near a wall, are convected towards the wall by the response of the high speed outer region fluid to the presence of the large-scale motions. This interaction establishes a phasing between the inner and outer regions. The length and velocity scales of the typical eddy are used to remove the Reynolds number dependence of the stream wise fluctuations and the Reynolds stress in the fully turbulent portion of turbulent boundary layers over a wide range of Reynolds numbers

A coherent structure model of the turbulent boundary layer and its ability to predict Reynolds number dependence

1991 ◽  
Vol 337 (1648) ◽  
pp. 573-574 ◽  
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Turbulence Intensity ◽  
Structure Model ◽  
Curve Fit ◽  
Line Parallel ◽  
Reynolds Number Dependence ◽  
Correct Expression

An error in the expression for the curve fit of C y / against R 0 has been discovered subsequent to publication. This was due to a software output statement error in the curve-fitting program. It influences all expressions derivative from it. The correct expression for the curve fit is C y / = 30.5R -0.71 . The derivative expressions and their locations in the paper, along with the corrected expressions are indicated below. As a consequence the curve fit of typical eddies in figure 9 of the paper is also incorrect. During the re-evaluation, we had the opportunity to use the experimentally measured values of u 7 obtained with the pocket data, and found that they resulted in a trend that more closely follows the corrected typical eddy data. The corrected typical eddy curve fit and pocket data are replotted below (a dashed line parallel to the typical eddy fit has been put through the pocket data for reference). The conclusion about the similar dependencies between the pockets and the typical eddies remains unchanged; however, the typical eddy scale is approximately 50% larger than the pocket scale. The normalization of the turbulence intensity and Reynolds stress data shown in figures 10 b and 11 b of the original paper has been recalculated using the correct expressions, and are also shown below. Although there is a quantitative shift of the data, the quality of the data collapse is seen to be essentially unaffected. Hence, all of the conclusions reached remain the same.

The ‘preferred mode’ of the axisymmetric jet

1981 ◽  
Vol 110 ◽  
pp. 39-71 ◽  
Author(s):  
A. K. M. F. Hussain ◽  
K. B. M. Q. Zaman
Keyword(s):  
Reynolds Number ◽  
Reynolds Stress ◽  
Coherent Structure ◽  
Large Scale ◽  
Near Field ◽  
Saddle Points ◽  
Initial Boundary ◽  
Phase Average ◽  
Background Turbulence ◽  
Time Average

The ‘preferred mode’ of an incompressible axisymmetric free jet has been organized through controlled perturbation, and spatial distributions of time-average as well as phase-average flow properties in the near field are documented. The excitation produces noticeable changes in the time-average measures of the jet, although these changes are less dramatic than those for the excitation producing stable vortex pairing. For different stages in the evolution of the preferred-mode coherent structure, the phase-average vorticity, coherent Reynolds stress, and incoherent turbulence intensities and Reynolds stress have been educed through phase-locked hot-wire measurements, over the spatial extent of the structure and without invoking the Taylor hypothesis. For a particular stage of the evolution (i.e. when the structure is centred at x/D ≃ 3) the distributions of these quantities have been compared for both initially laminar and fully turbulent exit boundary layers, and for four jet Reynolds numbers. The relative merits of the coherent structure streamline and pseudo-stream-function patterns, as compared with phase-average velocity contours, for structure boundary identification have been discussed. The structure shape and size agree closely with those inferred from the average streamline pattern of the natural structure educed by Yule (1978).These data as well as τ-spectra show that even excitation at the preferred mode cannot sustain the initially organized large-scale coherent structure beyond eight diameters from the jet exit. The background turbulence is organized by the coherent motions in such a way that the maximum rate of decrease of the coherent vorticity occurs at the structure centres which are the saddle points of the background-turbulence Reynolds-stress distributions. The structure centres are also the locations of peak phase-average turbulence intensities. The evolving shape of the structure as it travels downstream helps explain the transverse variations of the wavelength and convection velocity across the mixing layer. The coherent structure characteristics are found to be independent of whether the initial boundary layer is laminar or turbulent, but depend somewhat on the jet Reynolds number. With increasing Reynolds number, the structure decreases in the streamwise length and increases in the radial width and becomes relatively more energetic, and more efficient in the production of coherent Reynolds stress.

Pressure gradient effects on the large-scale structure of turbulent boundary layers

2013 ◽  
Vol 715 ◽  
pp. 477-498 ◽  
Author(s):  
Zambri Harun ◽  
Jason P. Monty ◽  
Romain Mathis ◽  
Ivan Marusic
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Amplitude Modulation ◽  
Large Scale ◽  
Outer Region ◽  
Adverse Pressure Gradient ◽  
Turbulent Boundary Layers ◽  
Small Scale

AbstractResearch into high-Reynolds-number turbulent boundary layers in recent years has brought about a renewed interest in the larger-scale structures. It is now known that these structures emerge more prominently in the outer region not only due to increased Reynolds number (Metzger & Klewicki, Phys. Fluids, vol. 13(3), 2001, pp. 692–701; Hutchins & Marusic, J. Fluid Mech., vol. 579, 2007, pp. 1–28), but also when a boundary layer is exposed to an adverse pressure gradient (Bradshaw, J. Fluid Mech., vol. 29, 1967, pp. 625–645; Lee & Sung, J. Fluid Mech., vol. 639, 2009, pp. 101–131). The latter case has not received as much attention in the literature. As such, this work investigates the modification of the large-scale features of boundary layers subjected to zero, adverse and favourable pressure gradients. It is first shown that the mean velocities, turbulence intensities and turbulence production are significantly different in the outer region across the three cases. Spectral and scale decomposition analyses confirm that the large scales are more energized throughout the entire adverse pressure gradient boundary layer, especially in the outer region. Although more energetic, there is a similar spectral distribution of energy in the wake region, implying the geometrical structure of the outer layer remains universal in all cases. Comparisons are also made of the amplitude modulation of small scales by the large-scale motions for the three pressure gradient cases. The wall-normal location of the zero-crossing of small-scale amplitude modulation is found to increase with increasing pressure gradient, yet this location continues to coincide with the large-scale energetic peak wall-normal location (as has been observed in zero pressure gradient boundary layers). The amplitude modulation effect is found to increase as pressure gradient is increased from favourable to adverse.

Generation mechanism of a hierarchy of vortices in a turbulent boundary layer

2019 ◽  
Vol 865 ◽  
pp. 1085-1109 ◽  
Author(s):  
Yutaro Motoori ◽  
Susumu Goto
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Energy Spectrum ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Generation Mechanism ◽  
Small Scale ◽  
Generation Process ◽  
Mean Flow ◽  
The Mean

To understand the generation mechanism of a hierarchy of multiscale vortices in a high-Reynolds-number turbulent boundary layer, we conduct direct numerical simulations and educe the hierarchy of vortices by applying a coarse-graining method to the simulated turbulent velocity field. When the Reynolds number is high enough for the premultiplied energy spectrum of the streamwise velocity component to show the second peak and for the energy spectrum to obey the$-5/3$power law, small-scale vortices, that is, vortices sufficiently smaller than the height from the wall, in the log layer are generated predominantly by the stretching in strain-rate fields at larger scales rather than by the mean-flow stretching. In such a case, the twice-larger scale contributes most to the stretching of smaller-scale vortices. This generation mechanism of small-scale vortices is similar to the one observed in fully developed turbulence in a periodic cube and consistent with the picture of the energy cascade. On the other hand, large-scale vortices, that is, vortices as large as the height, are stretched and amplified directly by the mean flow. We show quantitative evidence of these scale-dependent generation mechanisms of vortices on the basis of numerical analyses of the scale-dependent enstrophy production rate. We also demonstrate concrete examples of the generation process of the hierarchy of multiscale vortices.

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.

Experimental study of negatively buoyant finite-size particles in a turbulent boundary layer up to dense regimes

2019 ◽  
Vol 866 ◽  
pp. 598-629 ◽  
Author(s):  
Lucia J. Baker ◽  
Filippo Coletti
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Fluid Velocity ◽  
Outer Region ◽  
Finite Size ◽  
Working Fluid ◽  
Channel Height ◽  
Reynolds Stresses ◽  
Volume Fractions

We experimentally investigate the two-phase interplay in an open-channel turbulent boundary layer laden with finite-size particles at global volume fractions between 4 and 25 %. The working fluid (water) and the dispersed phase (hydrogel spheres) have closely matched refractive indices, allowing us to measure the properties of both phases using particle image velocimetry and particle tracking velocimetry, respectively. The particles have a diameter of approximately 9 % of the channel depth and are slightly denser than the fluid. The negative buoyancy causes a strong vertical concentration gradient, characterized by discrete and closely spaced particle layers parallel to the wall. Even at the lowest considered volume fractions, the near-wall fluid velocity and velocity gradients are strongly reduced, with large mean shear throughout most of the channel height. This indicates that the local effective viscosity of the suspension is greatly increased due to the friction between particle layers sliding over one another. The particles consistently lag the fluid and leave their footprint on its mean and fluctuating velocity profiles. The turbulent activity is damped near the wall, where the nearly packed particles disrupt and suppress large-scale turbulent fluctuations and redistribute some of the kinetic energy to smaller scales. On the other hand, in the outer region of the flow where the local particle concentration is low, the mean shear produces strong Reynolds stresses, with enhanced sweeps and ejections and frequent swirling events.

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