scholarly journals Turbulence at the Lee bound: maximally non-normal vortex filaments and the decay of a local dissipation rate

2019 ◽  
Vol 881 ◽  
pp. 283-312 ◽  
Author(s):  
Christopher J. Keylock
Keyword(s):  
Isotropic Turbulence ◽  
Total Strain ◽  
Normal Strain ◽  
Lagrangian Analysis ◽  
Conjugate Pair ◽  
Flow Topology ◽  
Positive Balance ◽  
Normal Production ◽  
The One ◽  
Production Dynamics

This paper uses a tight mathematical bound on the degree of the non-normality of the turbulent velocity gradient tensor to classify flow behaviour within vortical regions (where the eigenvalues of the tensor contain a conjugate pair). Structures attaining this bound are preferentially generated where enstrophy exceeds total strain and there is a positive balance between strain production and enstrophy production. Lagrangian analysis of homogeneous, isotropic turbulence shows that attainment of this bound is associated with relatively short durations and an upper limit to the spatial extent of the flow structures that is similar to the Taylor scale. An analysis of the dynamically relevant terms using a recently developed formulation (Keylock, J. Fluid Mech., vol. 848, 2018, pp. 876–904), highlights the controls on this dynamics. In particular, in high enstrophy regions it is shown that the bound is attained when normal strain decreases rather than when non-normality increases. The near absence of normal total strain results in a source of intermittency in the dynamics of dissipation that is hidden in standard analyses. It is shown that of the two terms that contribute to the non-normal production dynamics, it is the one that is typically smallest in magnitude that is of greatest importance within these $\ell =1$ filaments. The typical distance between filament centroids is just less than a Taylor scale, implying a connection to the manner in which flow topology at the Taylor scale explains dissipation at smaller scales.

scholarly journals Density effects on post-shock turbulence structure and dynamics

2019 ◽  
Vol 880 ◽  
pp. 935-968 ◽  
Author(s):  
Yifeng Tian ◽  
Farhad A. Jaberi ◽  
Daniel Livescu
Keyword(s):  
Shock Wave ◽  
Isotropic Turbulence ◽  
Joint Probability ◽  
Variable Density ◽  
Particle Methods ◽  
Turbulence Structure ◽  
Differential Distribution ◽  
Flow Topology ◽  
Turbulent Statistics ◽  
Post Shock

Turbulence structure resulting from multi-fluid or multi-species, variable-density isotropic turbulence interaction with a Mach 2 shock is studied using turbulence-resolving shock-capturing simulations and Eulerian (grid) and Lagrangian (particle) methods. The complex roles that density plays in the modification of turbulence by the shock wave are identified. Statistical analyses of the velocity gradient tensor (VGT) show that density variations significantly change the turbulence structure and flow topology. Specifically, a stronger symmetrization of the joint probability density function (PDF) of second and third invariants of the anisotropic VGT, PDF$(Q^{\ast },R^{\ast })$, as well as the PDF of the vortex stretching contribution to the enstrophy equation, are observed in the multi-species case. Furthermore, subsequent to the interaction with the shock, turbulent statistics also acquire a differential distribution in regions having different densities. This results in a nearly symmetric PDF$(Q^{\ast },R^{\ast })$ in heavy-fluid regions, while the light-fluid regions retain the characteristic tear-drop shape. To understand this behaviour and the return to ‘standard’ turbulence structure as the flow evolves away from the shock, Lagrangian dynamics of the VGT and its invariants is studied by considering particle residence times and conditional particle variables in different flow regions. The pressure Hessian contributions to the VGT invariants transport equations are shown to be not only affected by the shock wave, but also by the density in the multi-fluid case, making them critically important to the flow dynamics and turbulence structure.

scholarly journals Chaos and complexity in a simple model of production dynamics

2000 ◽  
Vol 5 (3) ◽  
pp. 179-187 ◽  
Author(s):  
I. Katzorke ◽  
A. Pikovsky
Keyword(s):  
Simple Model ◽  
Dynamical Behavior ◽  
Production Costs ◽  
Order Flow ◽  
One Dimensional ◽  
Dynamical Behaviors ◽  
The Stability ◽  
The One ◽  
Production Dynamics ◽  
Complex Dynamical Behavior

We consider complex dynamical behavior in a simple model of production dynamics, based on the Wiendahl’s funnel approach. In the case of continuous order flow a model of three parallel funnels reduces to the one-dimensional Bernoulli-type map, and demonstrates strong chaotic properties. The optimization of production costs is possible with the OGY method of chaos control. The dynamics changes drastically in the case of discrete order flow. We discuss different dynamical behaviors, the complexity and the stability of this discrete system.

Algebraic probability density tails in decaying isotropic two-dimensional turbulence

1996 ◽  
Vol 313 ◽  
pp. 223-240 ◽  
Author(s):  
Javier Jiménez
Keyword(s):  
Isotropic Turbulence ◽  
Cauchy Distribution ◽  
Two Dimensional ◽  
Scaling Properties ◽  
Velocity Gradients ◽  
Random Arrangement ◽  
Coherent Vortices ◽  
Statistical Argument ◽  
Decaying Turbulence ◽  
The One

The p.d.f. of the velocity gradients in two-dimensional decaying isotropic turbulence is shown to approach a Cauchy distribution, with algebraic s−2 tails, as the flow becomes dominated by a large number of compact coherent vortices. The statistical argument is independent of the vortex structure, and depends only on general scaling properties. The same argument predicts a Gaussian p.d.f. for the velocity components. The convergence to these limits as a function of the number of vortices is analysed. It is found to be fast in the former case, but slow (logarithmic) in the latter, resulting in residual u−3 tails in all practical cases. The influence of a spread Gaussian vorticity distribution in the cores is estimated, and the relevant dimensionless parameter is identified as the area fraction covered by the cores. A comparison is made with the result of numerical simulations of two-dimensional decaying turbulence. The agreement of the p.d.f.s is excellent in the case of the gradients, and adequate in the case of the velocities. In the latter case the ratio between energy and enstrophy is computed, and agrees with the simulations. All the one-point statistics considered in this paper are consistent with a random arrangement of the vortex cores, with no evidence of energy screening.

scholarly journals Knowledge Production at the Borderline Territory

2019 ◽  
pp. 144-149
Author(s):  
Lovorka Prpić
Keyword(s):  
Knowledge Production ◽  
Spatial Perception ◽  
Personality Development ◽  
Time Interval ◽  
Form Of Life ◽  
Experimental Process ◽  
School Laboratory ◽  
The One ◽  
Production Dynamics ◽  
The Magnetic Field

Learning, like creation, takes place in relation. Life happens in the interval of matter. In the magnetic field — space-time interval of change — a new form of life is created. Intention is to explore the incentive for knowledge production dynamics in education of architects through a lens of relational phenomena. Phenomenology of the inside-outside relation in spatial perception of architecture is compared to the one in psychoanalytical dynamics. In a culture of interconnectedness and change, architectural education is an experimental process. School-laboratory is an organized transient community of self-reflective individuals engaged within an active discovery-oriented atmosphere. Pedagogical approach is a nonhierarchical dialogue, individualized and emancipatory. Method can foster collaboration and/or induce instability; it sustains conflict, failure, and crisis. Reflective practice stimulates personality development in the process of individuation and actualization of potentials. Transformative encounter is an open process, an exchangeable relationship.

scholarly journals On Modelling Wind-Farm Wake Turbulence Autospectra and Coherence from a Database

Energies ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 120
Author(s):  
Kyle Schau ◽  
Gopal Gaonkar ◽  
Vaishakh Krishnan
Keyword(s):  
Complex Terrain ◽  
Wind Farm ◽  
Isotropic Turbulence ◽  
Perturbation Series ◽  
Homogeneous Isotropic Turbulence ◽  
Wake Turbulence ◽  
Scale Test ◽  
Computational Fluid Dynamics Cfd ◽  
The One ◽  
Research Avenue

This study addresses the feasibility of modeling wind-farm wake-turbulence autospectra and coherences from a database: flow velocity points from experimental and computational fluid dynamics (CFD) investigations. Specifically, it first applies an earlier-exercised framework to construct the autospectral models from a database and then it adopts a recently proposed framework to construct the coherence models from a database. While this proposed framework has not been tested against a database, the methodology has been completely formulated with a theoretical basis. These models of autospectrum and coherence are interpretive, and in closed form. Both frameworks basically involve the perturbation series expansion of the autospectra and coherences. The framework for modeling autospectra is tested against a demanding database of wake turbulence inside a wind farm over a complex terrain from a full-scale test. The suitability of these autospectral models for simulation through white-noise driven filters is also demonstrated. Finally, coherence models are generated for assumed values of the perturbation series constants, and these coherence models are used to demonstrate how the coherence models of homogeneous isotropic turbulence deviate from the coherence models of non-homogeneous non-isotropic turbulence such as wind-farm wake turbulence. This feasibility of extracting both the one-point statistics of autospectral models and the two-point statistics of coherence models from a database represents a research avenue that is new and promising in the treatment of wind-farm wake turbulence. This paper also demonstrates the feasibility of fruitfully exploiting the wake treatment methods developed in other fields.

scholarly journals THE RÔLE OF THE SPLEEN IN IRON METABOLISM AS ELUCIDATED BY CHANGES IN THE IRON BALANCE AFTER SPLENECTOMY

1933 ◽  
Vol 57 (1) ◽  
pp. 65-79 ◽  
Author(s):  
Elizabeth D. Wilson ◽  
Edward B. Krumbhaar
Keyword(s):  
Intact Animal ◽  
Weight Maintenance ◽  
Iron Intake ◽  
Loss Of Weight ◽  
Positive Balance ◽  
Balance Weight ◽  
Before And After ◽  
Definite Factor ◽  
Negative Balance ◽  
The One

We have estimated the iron balance in six dogs before and after splenectomy, in two intact dogs, and in five dogs before and after major operations other than splenectomy. In all the animals studied, considerable variation in iron balance was observed in the periods used (6 to 14 days). The intact controls had positive balances, the one followed for a year and a half having over 0.4 mg. per kilo per day, except when fasting or on an inadequate intake. The iron of urine, lost hair, dandruff, etc., which was not included in the determinations, would be far from sufficient to restore equilibrium. Of five animals subjected to major operations other than splenectomy, all of which in preoperative periods had positive balances varying between 0.423 mg. to 0.075 mg. per kilo per day, three showed a positive balance of from 0.989 mg. to 0.057 mg. and two showed negative balances of from 0.02 to 0.18 mg., the last two having anemia in the period of study while the others had none. Of the six splenectomized dogs, five showed a greater tendency to loss of iron after splenectomy (i.e., either a change from a positive to a negative balance or to an increasedly negative or lessened positive balance). This was not always apparent until some days after splenectomy and coincided approximately with the period of developing anemia. The removal of the spleen was usually found therefore to be transiently associated with increased excretion of iron. It is not possible to demonstrate, however, that the increased loss of iron is the cause of the anemia, and the matter awaits further investigation before the reason of its occurrence is made clear. An adequate iron intake in an intact animal was usually accompanied by a positive balance, though in splenectomized animals during the period of anemia it was frequently accompanied by a negative balance. Gain in weight in intact animals likewise was associated with a positive balance; but in the three instances in which gain of weight occurred during periods of anemia, after splenectomy or other operations, it was associated with a negative balance. Weight maintenance was also associated with a positive balance except in one instance of severe postsplenectomy anemia. Loss of weight was not sufficiently associated with a negative balance to make it seem a definite factor influencing the balance, per se, although about one-third of the periods of loss of weight were associated with negative balances.

Kinetics of gene expression in bacteria — From models to measurements, and back again

2013 ◽  
Vol 91 (7) ◽  
pp. 487-494 ◽  
Author(s):  
Andre S. Ribeiro
Keyword(s):  
Gene Expression ◽  
Stochastic Process ◽  
Stochastic Model ◽  
Experimental Validation ◽  
Live Cells ◽  
Genetic Circuits ◽  
Future Developments ◽  
The One ◽  
Kinetics Of ◽  
Production Dynamics

Dennis Salahub has contributed to several scientific areas. Likely, one of the lesser known contributions is the one on the study of the kinetics of gene expression in prokaryotes, which resulted in a delayed stochastic model of transcription and translation dynamics in bacteria. The model has become the basis for modeling stochastic genetic circuits and has provided a framework for interpreting recent measurements of transcripts production dynamics in live cells, one event at a time. Here, we review the contributions by Salahub and colleagues to the modeling strategies of gene expression as a multi-delayed stochastic process. Next, we describe recent findings, which build upon this work and provide experimental validation of the models. Finally, we discuss potential future developments in this field of research.

Influence of flow topology and dilatation on scalar mixing in compressible turbulence

2016 ◽  
Vol 793 ◽  
pp. 633-655 ◽  
Author(s):  
Mohammad Danish ◽  
Sawan Suman ◽  
Sharath S. Girimaji
Keyword(s):  
Isotropic Turbulence ◽  
Passive Scalar ◽  
Compressible Turbulence ◽  
Scalar Dissipation ◽  
Stable Node ◽  
Scalar Mixing ◽  
Flow Topology ◽  
Local Flow ◽  
Amplification Mechanism ◽  
Almost All

The kinematics of passive scalar mixing and its relation to local flow topology and dilatation in compressible turbulence are examined using direct numerical simulations (DNS) of decaying isotropic turbulence. The main objective of this work is to characterize the dependence of various evolution mechanisms of scalar dissipation on local streamline topology and normalized dilatation. The DNS results indicate that the topology has a stronger influence on the nonlinear amplification mechanism than the dilatation level of a fluid element. In its appropriately normalized form, the amplification mechanism is found to be fairly independent of the Mach and Reynolds numbers. Non-focal topologies (the so called unstable-node/saddle/saddle and stable-node/saddle/saddle) are found to be associated with more intense mixing than the focal topologies at almost all dilatation levels. Alignment tendencies (jointly conditioned upon topology and dilatation) between the scalar-gradient vector and the strain-rate eigenvectors are shown to play a key role in shaping the observed behaviour in compressible turbulence. Finally, some modelling implications of these findings are discussed.

Topological investigation of junction flow between cylinder and flat plate

2021 ◽  
pp. 095440622110007
Author(s):  
R Abhilash ◽  
Kwang-Yong Kim ◽  
S Anil Lal
Keyword(s):  
Reynolds Number ◽  
Reverse Flow ◽  
Saddle Points ◽  
Equation Model ◽  
Scale Model ◽  
Model Description ◽  
Flow Topology ◽  
Eddy Simulation ◽  
Junction Flow ◽  
The One

The paper presents a numerical investigation on the junction flow occurring at the intersection between a wall and a protruding circular cylinder. Simulations of flow for Reynolds number ( Re) in the range [125 - 20000] have been carried out using OpenFOAM, an open source CFD tool. Plots of stream tracers have been used to qualitatively characterize the flow topology as either attachment or separation based on the type of singular points, classified as nodes and saddle points. Quantitative variations of momentum flux have been applied to identify a key mechanism for the transition of topology using the relative momentum strength of the incoming and reverse flow. Effect of a thinner boundary layer has been assessed by (i) imposing a reduced wall shear stress, and (ii) increasing the Reynolds number. Features of a typical unsteady flow, in the transition regime, at Re = 20000 have been predicted using Large Eddy Simulation (LES) with a one-equation eddy viscosity sub-grid scale model. Description of the time evolution of the topology at Re = 20000 has been able to validate the one-equation model in OpenFoam as well as to further validate the key mechanism identified for topology transition.

scholarly journals The macro- and microeconomic approach of subsidies

2019 ◽  
Vol 2019 (105 (161)) ◽  
pp. 95-112
Author(s):  
Zsuzsanna Széles ◽  
Erzsébet Tóth-Szabó ◽  
Gábor Tóth
Keyword(s):  
Conceptual Approach ◽  
Positive Balance ◽  
Macroeconomic Impact ◽  
Emerging Issues ◽  
Net Method ◽  
Development Goals ◽  
The One ◽  
The Impact ◽  
The Eu ◽  
Budget Expenditure

Subsidies can come from domestic and EU sources, and they aim to cover costs and serve development goals. We have examined subsidies from two aspects: from the micro- and the macroeconomic approach. On the one hand, regarding the macroeconomic impact, we look at how their extent and components changed between 2004 and 2017, and also whether the impact of developments within the framework of cohesion subsidies on the budget was significant. Hungary has been among the net beneficiary Member States since its accession to the EU. The positive balance between 2004 and 2017 was more than 40 billion EUR In 2017, Poland (10.68%) and France (12.1%) were given the most significant subsidies, while Hungary received 3.68% of the total budget expenditure. On the other hand, from the microeconomic approach, the paper examines accounting and accountancy options and managing emerging issues. The analysis includes a conceptual approach to dealing with the problem in terms of the single accounting principles, the principle of comparability, and the principle of accruals. Two procedures can be applied to state support in the principle capital and income approach. It is an important difference that, in the net method, a subsidy becomes part of the equity immediately in the year of disbursement, while in the case of the gross method, only the life of the asset will be included in the equity in the current year by deducting the deferred income.

Sign in / Sign up

Export Citation Format

Share Document