Large organized structures in stably stratified turbulent shear flows.

2020 ◽  
Author(s):  
Andrey Glazunov ◽  
Evgeny Mortikov ◽  
Grigory Zasko ◽  
Yuri Nechepurenko ◽  
Sergej Zilitinkevich
Keyword(s):  
Shear Flows ◽  
Spatial Scales ◽  
Basic Research ◽  
Field Measurements ◽  
Stable Stratification ◽  
Thin Layers ◽  
Turbulent Shear ◽  
Large Temperature ◽  
Turbulent Shear Flows ◽  
Optimal Disturbances

<p>We analyzed the data of the numerical simulation of stably stratified turbulent shear flows. It is shown that, along with chaotic turbulence, the flows contain large organized structures. In the temperature field, these structures appear as inclined layers with weakly stable stratification, separated by very thin layers with large temperature gradients. The existence of such layered structures in nature is indirectly confirmed by the analysis of field measurements. An increase of the turbulent Prandtl number with increasing gradient Richardson number was fixed in simulation data. The hypothesis is proposed that physical mechanism for maintaining of turbulence in supercritically stable stratification is connected with the revealed  structures. It is shown that the spatial scales and the shapes of the identified organized structures can be explained using the calculation of  optimal disturbances for the simplified linear model.</p><p>This study was supported by the Russian Foundation for Basic Research (grants nos. 18-05-60126,  20-05-00776) and by Academy of Finland project ClimEco no. 314 798/799 (2018-2020).</p>

scholarly journals Frequency–wavenumber mapping in turbulent shear flows

2015 ◽  
Vol 783 ◽  
pp. 166-190 ◽  
Author(s):  
Roeland de Kat ◽  
Bharathram Ganapathisubramani
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Shear Flows ◽  
Spatial Scales ◽  
Turbulent Shear ◽  
Data Set ◽  
Frequency Spectra ◽  
Taylor’S Hypothesis ◽  
Turbulent Shear Flows ◽  
High Reynolds

Spatial turbulence spectra for high-Reynolds-number shear flows are usually obtained by mapping experimental frequency spectra into wavenumber space using Taylor’s hypothesis, but this is known to be less than ideal. In this paper, we propose a cross-spectral approach that allows us to determine the entire wavenumber–frequency spectrum using two-point measurements. The method uses cross-spectral phase differences between two points – equivalent to wave velocities – to reconstruct the wavenumber–frequency plane, which can then be integrated to obtain the spatial spectrum. We verify the technique on a particle image velocimetry (PIV) data set of a turbulent boundary layer. To show the potential influence of the different mappings, the transfer functions that we obtained from our PIV data are applied to hot-wire data at approximately the same Reynolds number. Comparison of the newly proposed technique with the classic approach based on Taylor’s hypothesis shows that – as expected – Taylor’s hypothesis holds for larger wavenumbers (small spatial scales), but there are significant differences for smaller wavenumbers (large spatial scales). In the range of Reynolds number examined in this study, double-peaked spectra in the outer region of a turbulent wall flow are thought to be the result of using Taylor’s hypothesis. This is consistent with previous studies that focused on examining the limitations of Taylor’s hypothesis (del Álamo & Jiménez, J. Fluid Mech., vol. 640, 2009, pp. 5–26). The newly proposed mapping method provides a data-driven approach to map frequency spectra into wavenumber spectra from two-point measurements and will allow the experimental exploration of spatial spectra in high-Reynolds-number turbulent shear flows.

Toward full-field measurements of instantaneous visualizations of coherent structures in turbulent shear flows

1990 ◽  
Vol 3 (1) ◽  
pp. 74-86 ◽  
Author(s):  
Laertis Economikos ◽  
Craig Shoemaker ◽  
Keith Russ ◽  
Robert S. Brodkey ◽  
Dave Jones
Keyword(s):  
Coherent Structures ◽  
Shear Flows ◽  
Field Measurements ◽  
Turbulent Shear ◽  
Full Field ◽  
Turbulent Shear Flows

scholarly journals Emergence of optimal disturbances in a stratified turbulent shear flow under the stochastic forcing

2021 ◽  
Vol 2099 (1) ◽  
pp. 012033
Author(s):  
G V Zasko ◽  
P A Perezhogin ◽  
A V Glazunov ◽  
E V Mortikov ◽  
Y M Nechepurenko
Keyword(s):  
Large Scale ◽  
Spatial Scales ◽  
Field Measurements ◽  
Turbulent Shear ◽  
Small Scale ◽  
Turbulent Shear Flow ◽  
Stochastic Forcing ◽  
Stable Atmospheric Boundary Layer ◽  
Scale Turbulence ◽  
Optimal Disturbances

Abstract Large-scale inclined organized structures in stably stratified turbulent shear flows were revealed in the numerical simulation and indirectly confirmed by the field measurements in the stable atmospheric boundary layer. Spatial scales and forms of these structures coincide with those of the optimal disturbances of a simplified linear model. In this paper, we clarify the relation between the organized structures and the optimal disturbances, analyzing a time series of turbulent fields obtained by the RANS model with eddy viscosity/diffusivity and stochastic forcing generating the small-scale turbulence.

scholarly journals The layered structure of stably stratified turbulent shear flows

2019 ◽  
Vol 55 (4) ◽  
pp. 13-26
Author(s):  
A. V. Glazunov ◽  
E. V. Mortikov ◽  
K. V. Barskov ◽  
E. V. Kadancev ◽  
S. S. Zilitinkevich
Keyword(s):  
Numerical Simulation ◽  
Temperature Gradient ◽  
Richardson Number ◽  
Numerical Models ◽  
Measurement Data ◽  
Stable Stratification ◽  
Thin Layers ◽  
Turbulent Shear ◽  
Large Temperature ◽  
Turbulent Heat

The data of numerical simulation of stably stratified turbulent Couette flows are analyzed for various values of the Richardson number. Two different methods were used: Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES). It is shown that the flow contains large organized structures, along with chaotic turbulence, regardless of the simulation method. These structures appear as inclined layers in the temperature field with weakly stable stratification, separated by very thin layers with large temperature gradients. The existence of such layered structures in nature is indirectly confirmed by the analysis of field measurement data on the meteorological mast, where temperature gradient distribution histograms are found to be far from the normal distribution and similar to temperature gradient probability distributions obtained by numerical models data. The simulations indicate an increase of the turbulent Prandtl number with increasing of the gradient Richardson number. It is highly likely that the identified structures serve as effective barriers for vertical turbulent heat flux, without the blocking of momentum transfer. We proposed the hypothesis, that it is precisely these structures that serve as the physical mechanism for maintaining turbulence under supercritically stable stratification.

Unsteady Behavior of Turbulent Shear Flows

1990 ◽  
Author(s):  
Chih-Ming Ho ◽  
P. Huerre ◽  
L. G. Redekopp
Keyword(s):  
Shear Flows ◽  
Turbulent Shear ◽  
Turbulent Shear Flows ◽  
Unsteady Behavior

MEMS-Based Diagnostics for Turbulent Shear Flows.

1997 ◽  
Author(s):  
Ari Glezer ◽  
Mark Allen ◽  
Martin Brooke
Keyword(s):  
Shear Flows ◽  
Turbulent Shear ◽  
Turbulent Shear Flows
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