The role of coherent vortices near the turbulent/non-turbulent interface in a planar jet

2011 ◽  
Vol 369 (1937) ◽  
pp. 738-753 ◽  
Author(s):  
Carlos Bettencourt da Silva ◽  
Ricardo José Nunes dos Reis
Keyword(s):  
Numerical Simulation ◽  
Large Scale ◽  
Vortical Structures ◽  
Micro Scale ◽  
Planar Jet ◽  
Coherent Vortices ◽  
The Mean ◽  
Turbulent Plane ◽  
Plane Jet

The role of coherent vortices near the turbulent/non-turbulent (T/NT) interface in a turbulent plane jet is analysed by a direct numerical simulation (DNS). The coherent vortices near the jet edge consist of large-scale vortical structures (LSVSs) maintained by the mean shear and intense vorticity structures (IVSs) created by the background fluctuating turbulence field. The radius of the LSVS is equal to the Taylor micro-scale R lsvs ≈ λ , while the radius of the IVS is of the order of the Kolmogorov micro-scale R ivs ∼ η . The LSVSs are responsible for the observed vorticity jump at the T/NT interface, being of the order of the Taylor micro-scale. The coherent vortices in the proximity of the T/NT interface are preferentially aligned with the tangent to the T/NT interface and are responsible for the viscous dissipation of kinetic energy near the T/NT interface and to the characteristic shape of the enstrophy viscous diffusion observed at that location.

Drivers of biases in the extratropical storm tracks in CMIP6

2020 ◽  
Author(s):  
Matthew Priestley ◽  
Duncan Ackerley ◽  
Jennifer Catto ◽  
Kevin Hodges ◽  
Ruth McDonald ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Storm Track ◽  
Storm Tracks ◽  
Extratropical Cyclones ◽  
Ocean Coupling ◽  
Coupled Climate Models ◽  
The Mean ◽  
The Impact

<p>Extratropical cyclones are the leading driver of the day-to-day weather variability and wintertime losses for Europe. In the latest generation of coupled climate models, CMIP6, it is hoped that with improved modelling capabilities come improvements in the structure of the storm track and the associated cyclones. Using an objective cyclone identification and tracking algorithm the mean state of the storm tracks in the CMIP6 models is assessed as well as the representation of explosively deepening cyclones. Any developments and improvements since the previous generation of models in CMIP5 are discussed, with focus on the impact of model resolution on storm track representation. Furthermore, large-scale drivers of any biases are investigated, with particular focus on the role of atmosphere-ocean coupling via associated AMIP simulations and also the influence of large-scale dynamical and thermodynamical features.</p>

scholarly journals MHD simulations of star-disk magnetospheres and the formation of outflows and jets

2007 ◽  
Vol 3 (S243) ◽  
pp. 265-276
Author(s):  
Christian Fendt
Keyword(s):  
Numerical Simulation ◽  
Stellar Wind ◽  
Large Scale ◽  
Disk Surface ◽  
Time Dependent ◽  
Mhd Simulations ◽  
Tremendous Progress ◽  
Stellar Magnetospheres ◽  
Scale Evolution

AbstractIn this review the recent development concerning the large-scale evolution of stellar magnetospheres in interaction with the accretion disk is discussed. I put emphasis on the generation of outflows and jets from the disk and/or the star. In fact, tremendous progress has occurred over the last decade in the numerical simulation of the star-disk interaction. The role of numerical simulations is essential in this area because the processes involved are complex, strongly interrelated, and often highly time-dependent. Recent MHD simulations suggest that outflows launched from a very concentrated region tend to be un-collimated. I present preliminary results of simulations of large-scale star-disk magnetospheres loaded with matter from the stellar, resp. the disk surface demonstrating how a disk jet collimates the wind from the star and also how the stellar wind lowers the collimation degree of the disk outflow.

On the influence of coherent structures upon interscale interactions in turbulent plane jets

2002 ◽  
Vol 473 ◽  
pp. 103-145 ◽  
Author(s):  
C. B. da SILVA ◽  
O. MÉTAIS
Keyword(s):  
Kinetic Energy ◽  
Coherent Structures ◽  
Energy Transport ◽  
Local Equilibrium ◽  
Coherent Vortices ◽  
Free Shear Layers ◽  
Plane Jets ◽  
Energy Exchanges ◽  
Turbulent Plane ◽  
Plane Jet

The influence of the coherent structures on grid/subgrid-scale (GS/SGS) interactions in free shear layers is analysed through the application of a top-hat filter to several plane jet direct numerical simulations (DNS). The Reynolds number based on the plane jet inlet slot width is Reh = 3000. The study deals with energy containing (Kelvin–Helmholtz) and inertial range (streamwise) vortices, from the far field of the turbulent plane jet. The most intense kinetic energy exchanges between GS and SGS occur near these structures and not randomly in the space. The GS kinetic energy is dominated by GS advection and GS pressure/velocity interactions which appear located next to the Kelvin–Helmholtz rollers. Surprisingly, GS/SGS transfer is not very well correlated with the coherent vortices and GS/SGS diffusion plays an important role in the local dynamics of both GS and SGS kinetic energy. The so-called ‘local equilibrium assumption’ holds globally but not locally as most viscous dissipation of SGS kinetic energy takes place within the vortex cores whereas forward and backward GS/SGS transfer occurs at quite different locations. Finally, it was shown that SGS kinetic energy advection may be locally large as compared to the other terms of the SGS kinetic energy transport equation.

scholarly journals Hierarchical Porous Polyamide 6 by Solution Foaming: Synthesis, Characterization and Properties

Polymers ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 1310 ◽  
Author(s):  
Liang Wang ◽  
Yu-Ke Wu ◽  
Fang-Fang Ai ◽  
Jie Fan ◽  
Zhao-Peng Xia ◽  
...  
Keyword(s):  
Large Scale ◽  
Polyamide 6 ◽  
Solution Concentration ◽  
The Novel ◽  
Foaming Agent ◽  
Hierarchical Porous ◽  
Wide Range ◽  
The Mean ◽  
Novel Strategy

Porous polym er materials have received great interest in both academic and industrial fields due to their wide range of applications. In this work, a porous polyamide 6 (PA6) material was prepared by a facile solution foaming strategy. In this approach, a sodium carbonate (SC) aqueous solution acted as the foaming agent that reacted with formic acid (FA), generating CO2 and causing phase separation of polyamide (PA). The influence of the PA/FA solution concentration and Na2CO3 concentration on the microstructures and physical properties of prepared PA foams were investigated, respectively. PA foams showed a hierarchical porous structure along the foaming direction. The mean pore dimension ranged from hundreds of nanometers to several microns. Low amounts of sodium salt generated from a neutralization reaction played an important role of heterogeneous nucleation, which increased the crystalline degree of PA foams. The porous PA materials exhibited low thermal conductivity, high crystallinity and good mechanical properties. The novel strategy in this work could produce PA foams on a large scale for potential engineering applications.

Assessment of local isotropy using measurements in a turbulent plane jet

1986 ◽  
Vol 163 ◽  
pp. 365-391 ◽  
Author(s):  
R. A. Antonia ◽  
F. Anselmet ◽  
A. J. Chambers
Keyword(s):  
Large Scale ◽  
Spatial Organization ◽  
Structure Functions ◽  
Small Scale ◽  
Temperature Structure ◽  
Local Isotropy ◽  
Large Scale Motion ◽  
Turbulent Plane ◽  
Scale Motion ◽  
Plane Jet

Following a review of the difficulties associated with the measurement and interpretation of statistics of the small-scale motion, the evidence for and against local isotropy is assessed in the light of measurements in a turbulent plane jet at moderate values of the Reynolds and Péclet numbers. These measurements include spatial derivatives with respect to different spatial directions of the longitudinal velocity fluctuation and of the temperature fluctuation. Relations between mean-square values of these derivatives suggest strong departures from local isotropy for both velocity and temperature. In contrast, the locally isotropic forms of the vorticity and temperature dissipation budgets are approximately satisfied. Possible contamination of the fine-scale measurements by the anisotropic large-scale motion is assessed in the context of the measured structure functions of temperature and of the measured skewness of the streamwise derivative of temperature. Structure functions are, within the framework of local isotropy, consistent with the average frequency and amplitude of temperature signatures that characterize the quasi-organized large-scale motion. Conditional averages associated with this motion account, in an approximate way, for the skewness of the temperature derivative but make negligible contributions to the skewness of velocity derivatives. The degree of spatial organization of the fine structure is inferred from conditional statistics of temperature derivatives.

Convective Heat Transfer in Turbulent Flow Near a Gap

2006 ◽  
Vol 128 (7) ◽  
pp. 701-708 ◽  
Author(s):  
D. Chang ◽  
S. Tavoularis
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Large Scale ◽  
Stokes Equations ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Vortical Structures

Convective heat transfer in a rectangular duct containing a heated rod forming a narrow gap with a plane wall has been simulated by solving the unsteady Reynolds-averaged Navier-Stokes equations with a Reynolds stress model. Of particular interest is the role of quasi-periodic coherent structures in transporting fluid and heat across the gap region. It is shown that the local instantaneous velocity and temperature vary widely because of large-scale transport by coherent vortical structures forming in pairs on either side of the rod.

scholarly journals The electromotive force in multi-scale flows at high magnetic Reynolds number

2015 ◽  
Vol 81 (6) ◽  
Author(s):  
Steven M. Tobias ◽  
Fausto Cattaneo
Keyword(s):  
Reynolds Number ◽  
Electromotive Force ◽  
Large Scale ◽  
Magnetic Reynolds Number ◽  
Small Scale ◽  
Dynamo Theory ◽  
Multi Scale ◽  
The Mean ◽  
Scale Shear

Recent advances in dynamo theory have been made by examining the competition between small- and large-scale dynamos at high magnetic Reynolds number $\mathit{Rm}$. Small-scale dynamos rely on the presence of chaotic stretching whilst the generation of large-scale fields occurs in flows lacking reflectional symmetry via a systematic electromotive force (EMF). In this paper we discuss how the statistics of the EMF (at high $\mathit{Rm}$) depend on the properties of the multi-scale velocity that is generating it. In particular, we determine that different scales of flow have different contributions to the statistics of the EMF, with smaller scales contributing to the mean without increasing the variance. Moreover, we determine when scales in such a flow act independently in their contribution to the EMF. We further examine the role of large-scale shear in modifying the EMF. We conjecture that the distribution of the EMF, and not simply the mean, largely determines the dominant scale of the magnetic field generated by the flow.

scholarly journals The role of anogenital distance in the incidence risk of prostate cancer in China

2021 ◽  
Author(s):  
jiatong zhou ◽  
ranlu liu
Keyword(s):  
Prostate Cancer ◽  
Benign Prostatic Hyperplasia ◽  
Prostate Biopsy ◽  
Large Scale ◽  
Prostatic Hyperplasia ◽  
Anogenital Distance ◽  
Incidence Risk ◽  
The Mean ◽  
Androgen Levels

Abstract Background: Anogenital distance（AGD） can be used as a biomarker to indirectly indicate androgen levels during the sexual maturation of mammals. In order to gain a deeper understanding of the association between the AGD and the risk of prostate cancer(PCa), we performed this studyMaterials: A total of 107 patients undergoing perineal prostate biopsy from November 2019 to August 2020 were enrolled. All patients diagnosed 57 PCa patients and 50 benign prostatic hyperplasia(BPH) patients through perineal prostate biopsy in our hospital . The anus to the posterior base of the scrotum (AGDAS) and the cephalad insertion of the penis (AGDAP) of all patients were measured before prostate biopsy.Result: The mean age of patients with PCa was 69.46 ± 7.52 and the mean age of patients with BPH was 67.38± 8.26. We did not find a significant association between age and BMI in the risk of PCa(all p＞0.05). Besides, there was no significant association between AGD and the risk of PCa(p＞0.05). we only discovered that PSA could play an important role in the development of PCa.Conclusion: AGD may not play an important role in predicting the incidence risk of PCa. we still need a large-scale prospective study to explore the ture association between AGD and the incidence of PCa.

On new scaling laws in a temporally evolving turbulent plane jet using Lie symmetry analysis and direct numerical simulation

2018 ◽  
Vol 854 ◽  
pp. 233-260 ◽  
Author(s):  
H. Sadeghi ◽  
M. Oberlack ◽  
M. Gauding
Keyword(s):  
Scaling Laws ◽  
Stokes Equations ◽  
Lie Symmetry ◽  
Symmetry Analysis ◽  
Navier Stokes ◽  
Higher Moments ◽  
Lie Symmetry Analysis ◽  
The Mean ◽  
Turbulent Plane ◽  
Plane Jet

A temporally evolving turbulent plane jet is studied both by direct numerical simulation (DNS) and Lie symmetry analysis. The DNS is based on a high-order scheme to solve the Navier–Stokes equations for an incompressible fluid. Computations were conducted at Reynolds number $\mathit{Re}_{0}=8000$, where $\mathit{Re}_{0}$ is defined based on the initial jet thickness, $\unicode[STIX]{x1D6FF}_{0.5}(0)$, and the initial centreline velocity, $\overline{U}_{1}(0)$. A symmetry approach, known as the Lie group, is used to find symmetry transformations, and, in turn, group invariant solutions, which are also denoted as scaling laws in turbulence. This approach, which has been extensively developed to create analytical solutions of differential equations, is presently applied to the mean momentum and two-point correlation equations in a temporally evolving turbulent plane jet. The symmetry analysis of these equations allows us to derive new invariant (self-similar) solutions for the mean flow and higher moments of the velocities in the jet flow. The current DNS validates the consequence of Lie symmetry analysis and therefore confirms the establishment of novel scaling laws in turbulence. It is shown that the classical scaling law for the mean velocity is a specific form of the current scaling (which has a more general form); however, the scaling for the second and higher moments (such as Reynolds stresses) has a completely different structure compared to the classical scaling. While the failure of the classical scaling for the second moments of the fluctuating velocities has been noted from the jet data for many years, the DNS results nicely match with the present self-similar relations derived from Lie symmetry analysis. Key ingredients for the present results, in particular for the scaling laws of the higher moments, are symmetries, which are of a purely statistical nature. i.e. these symmetries are admitted by the moment equations, however, they are not observed by the original Navier–Stokes equations.

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