scholarly journals Observations of Stably Stratified Shear-Driven Atmospheric Turbulence at Low and High Richardson Numbers

2007 ◽  
Vol 64 (2) ◽  
pp. 645-655 ◽  
Author(s):  
Thorsten Mauritsen ◽  
Gunilla Svensson
Keyword(s):  
Velocity Field ◽  
Kinetic Energy ◽  
Potential Energy ◽  
Richardson Number ◽  
Stability Parameter ◽  
Stable Regime ◽  
Scalar Fluxes ◽  
Gradient Richardson Number ◽  
Weakly Stable ◽  
The Stability

Abstract Stably stratified shear-driven turbulence is analyzed using the gradient Richardson number, Ri, as the stability parameter. The method overcomes the statistical problems associated with the widely used Monin–Obukhov stability parameter. The results of the Ri-based scaling confirm the presence of three regimes: the weakly and the very stable regimes and the transition in between them. In the weakly stable regime, fluxes scale in proportion with variance, while in the very stable regime, stress and scalar fluxes behave differently. At large Ri, the velocity field becomes highly anisotropic and the turbulent potential energy becomes approximately equal to half of the turbulent kinetic energy. It appears that even in the strongly stable regime, beyond what is known as the critical gradient Richardson number, turbulent motions are present.

Les travaux sur la turbulence : les origines, Toucans, Cost-ES0905 et influence de l'entropie

2021 ◽  
pp. 079
Author(s):  
Ivan Bašták Ďurán ◽  
Pascal Marquet
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Richardson Number ◽  
Stable Stratification ◽  
Turbulence Energy ◽  
Third Order ◽  
Length Scales ◽  
Gradient Richardson Number ◽  
Turbulence Length ◽  
Consistent Treatment

Le schéma de turbulence Toucans est utilisé dans la configuration opérationnelle Alaro du modèle Aladin depuis début 2015. Son développement a été initié, guidé et en grande partie conçu par Jean-François Geleyn. Ce développement a commencé avec le prédécesseur du schéma Toucans, le schéma « pseudo-pronostique » en énergie cinétique turbulente, lui-même basé sur l'ancien schéma de turbulence de Louis, mais étendu dans Toucans à un schéma pronostique. Le schéma Toucans a pour objectif de traiter de manière cohérente les fonctions qui dépendent de la stabilité verticale de l'atmosphère, de l'influence de l'humidité et des échelles de longueur de la turbulence (de mélange et de dissipation). De plus, de nouvelles caractéristiques ont été ajoutées : une représentation améliorée pour les stratifications très stables (absence de nombre de Richardson critique), une meilleure représentation de l'anisotropie, un paramétrage unifié de la turbulence et des nuages par l'ajout d'une deuxième énergie turbulente pronostique et la paramétrisation des moments du troisième ordre. The Toucans turbulence scheme is a turbulence scheme that is used in the operational Alaro configuration of the Aladin model since early 2015. Its development was initiated, guided and to a large extend authored by Jean-François Geleyn. The development started with the predecessor of the Toucans scheme, the "pseudo-prognostic" turbulent kinetic energy scheme which itself was built on the "Louis" turbulence scheme, but extended to a prognostic scheme. The Toucans scheme aims for a consistent treatment of stability dependency functions, influence of moisture, and turbulence length scales. Additionally, new features were added to the turbulence scheme: improved representation of turbulence in very stable stratification (absence of critical gradient Richardson number), better representation of anisotropy, unified parameterization of turbulence and clouds via addition of second prognostic turbulence energy, and parameterization of third order moments.

scholarly journals Nighttime wind and scalar variability within and above an Amazonian canopy

2018 ◽  
Vol 18 (5) ◽  
pp. 3083-3099 ◽  
Author(s):  
Pablo E. S. Oliveira ◽  
Otávio C. Acevedo ◽  
Matthias Sörgel ◽  
Anywhere Tsokankunku ◽  
Stefan Wolff ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Low Frequency ◽  
Amazon Forest ◽  
Stable Regime ◽  
Stable Conditions ◽  
Weakly Stable ◽  
The Stability ◽  
The Relationship ◽  
Temporal Windows ◽  
Scalar Variability

Abstract. Nocturnal turbulent kinetic energy (TKE) and fluxes of energy, CO2 and O3 between the Amazon forest and the atmosphere are evaluated for a 20-day campaign at the Amazon Tall Tower Observatory (ATTO) site. The distinction of these quantities between fully turbulent (weakly stable) and intermittent (very stable) nights is discussed. Spectral analysis indicates that low-frequency, nonturbulent fluctuations are responsible for a large portion of the variability observed on intermittent nights. In these conditions, the low-frequency exchange may dominate over the turbulent transfer. In particular, we show that within the canopy most of the exchange of CO2 and H2O happens on temporal scales longer than 100 s. At 80 m, on the other hand, the turbulent fluxes are almost absent in such very stable conditions, suggesting a boundary layer shallower than 80 m. The relationship between TKE and mean winds shows that the stable boundary layer switches from the very stable to the weakly stable regime during intermittent bursts of turbulence. In general, fluxes estimated with long temporal windows that account for low-frequency effects are more dependent on the stability over a deeper layer above the forest than they are on the stability between the top of the canopy and its interior, suggesting that low-frequency processes are controlled over a deeper layer above the forest.

The structures and energetics of fully nonlinear symmetric baroclinic waves

1984 ◽  
Vol 142 ◽  
pp. 343-362 ◽  
Author(s):  
Timothy L. Miller
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Richardson Number ◽  
Vertical Plane ◽  
Vertical Motion ◽  
Zonal Flow ◽  
Meridional Flow ◽  
Average Kinetic Energy ◽  
Basic Solution ◽  
Baroclinic Waves

A finite-difference Navier-Stokes model has been used to study rotating baroclinic flow for Richardson number [lsim ] 1, assuming no variations except in the vertical plane wholly containing the density-gradient vector. A section of a horizontally infinite channel has been studied, assuming periodic boundary conditions at the vertical computational boundaries and no-slip conducting horizontal boundaries. Two configurations were studied, both of which have an analytic basic solution with no horizontal variations in the velocities or density gradients. Symmetric baroclinic waves developed in the flows, as long as the Richardson number was not too large and the thermal Rossby number was large enough (for fixed diffusion parameters), consistent with linear theory. The structures and energetics of the fully developed waves were found to be especially dependent upon the Prandtl number Pr. Potential energy was the ultimate wave-energy source in all cases, and the average zonal flow was never much affected by the waves. For Pr > 1 the conversion from potential energy to wave kinetic energy was direct, via temperature and vertical-motion correlation. For Pr < 1 the conversion was from potential energy, to average kinetic energy by virtue of an induced meridional flow, to wave kinetic energy. For Pr = 1 the energy conversion was by either or both of the above, depending upon the other parameters.

scholarly journals Boundary Layer Stability Regime at DACCIWA Site Using Gradient Richardson Number

2019 ◽  
pp. 402-415
Author(s):  
O. O. Ajileye ◽  
M. A. Ayoola
Keyword(s):  
Boundary Layer ◽  
Richardson Number ◽  
Meteorological Data ◽  
Boundary Layer Stability ◽  
Agricultural Field ◽  
Unstable Regime ◽  
Stable Regime ◽  
Gradient Richardson Number ◽  
Stability Regime ◽  
Neutral Conditions

Meteorological data including air temperature and wind speed which were collected from DACCIWA measurement site at a tropical agricultural field site in Ile-Ife (7.55oE, 4.56oE), south-western Nigeria have been used to classify boundary layer stability regimes using gradient Richardson number. Three categories were considered to deduce the pattern of stability conditions namely stable, unstable and neutral conditions for 3-hourly intervals at 0.00, 03.00, 06.00, 09.00, 12.00, 15.00, 18.00 and 21.00 hours from 15th June to 31st July 2016. The data were sampled every 1sec and stored subsequently as 10 minutes averages for all the measured parameters. The data was further reduced to 30 minutes averages for easy analysis and manipulation in the calculation of gradient Richardson number used for boundary layer stability regime characterization. The results showed that the month of June 2016 had prevalence of stable regime from 0:00 – 6:00 am and 6:00 pm; 9:00 am was predominantly neutral and shared similar pattern with 9:00 pm. Unstable regime was slightly observed at 12:00 pm and majorly observed at 3:00 pm. The month of July had a little shift from what was observed in the month of June. Predominance of neutral conditions was observed from 9:00 pm to 9:00 am; Hours of 12:00 – 3:00 pm were dominated by unstable regime while 6:00 pm was dominated by stable regime.

On the stability of the three-phase synchronous motor

1933 ◽  
Vol 29 (4) ◽  
pp. 528-535
Author(s):  
W. H. Ingram
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Position Angle ◽  
Alternating Current ◽  
The Self ◽  
Rotor Position ◽  
Three Phase ◽  
The Stability ◽  
Image Position ◽  
External Forces

A three-phase star-connected alternating-current motor of simplest type, connected to busbars maintained at sinusoidal potentials e1, e2 and e3 with respect to the star-point and connected to a shaft load which exerts a reactive torque f on the rotor, is dynamically specified by the following functions:where the are the armature currents in the three phases, i is the current in the amortisseur circuit, Q the current in the field circuit, θ the rotor position angle, T the kinetic energy, V the potential energy, S the Rayleigh dissipation and U the activity of the external forces on the machine. The self-inductances of the armature circuits and the mutual inductances between them are assumed to be constant.

A numerical study of the evolution and structure of homogeneous stably stratified sheared turbulence

1992 ◽  
Vol 237 ◽  
pp. 499-539 ◽  
Author(s):  
Steven E. Holt ◽  
Jeffrey R. Koseff ◽  
Joel H. Ferziger
Keyword(s):  
Kinetic Energy ◽  
Potential Energy ◽  
Turbulent Kinetic Energy ◽  
Richardson Number ◽  
Schmidt Number ◽  
Numerical Study ◽  
Stable Stratification ◽  
Neutral Buoyancy ◽  
Associated Production ◽  
Vertical Density

The structure and evolution of homogeneous stably stratified sheared turbulence have been investigated through direct numerical simulation. In these simulations the primary dimensionless parameter is the Richardson number which measures the relative importance of stratification and mean shear.For Richardson numbers less than the transition value the Reynolds stress and vertical density flux are down-gradient. Some of the vertical kinetic energy gained indirectly through production is expended in creating potential energy. Included in this shear-dominated regime is the stationary Richardson number at which the turbulent kinetic energy is constant in time although the spectra are evolving. At low dimensionless shear rate the stationary Richardson number increases with increasing Reynolds number.At the transition Richardson number the maximum anisotropy and energy partition are achieved. For larger Richardson numbers potential energy is released into vertical kinetic energy and the vertical density flux becomes counter-gradient. The associated production reversal enhances the decay rate of the turbulent kinetic energy.The effects of other dimensionless parameters have been investigated. After initial transients the developed flow is rather insensitive to the presence of significant initial potential energy. An increase in the Schmidt number increases the effect of stable stratification, e.g. the counter-gradient vertical density flux occurs earlier.In the shear dominated case the down-gradient fluxes are produced by the pumping of fluid through coherent hairpin-shaped vorticity. In the buoyancy dominated flow the counter-gradient fluid parcels induce helical vorticity structures as they move toward a position of neutral buoyancy.

scholarly journals Turbulent and non-turbulent exchange of scalars between the forest and the atmosphere at night in Amazonia

2017 ◽  
Author(s):  
Pablo E. S. Oliveira ◽  
Otávio C. Acevedo ◽  
Matthias Sörgel ◽  
Anywhere Tsokankunku ◽  
Stefan Wolff ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Low Frequency ◽  
Amazon Forest ◽  
Turbulent Transfer ◽  
Stable Regime ◽  
Stable Conditions ◽  
Weakly Stable ◽  
The Stability ◽  
The Relationship ◽  
Temporal Windows

Abstract. Nocturnal turbulent kinetic energy (TKE) and fluxes of energy, CO2 and O3 between the Amazon forest and the atmosphere are evaluated for a 20-day campaign at the Amazon Tall Tower Observatory (ATTO) site. The distinction of these quantities between fully turbulent (weakly stable) and intermittent (very stable) nights is discussed. Spectral analysis indicates that low-frequency, non-turbulent fluctuations are responsible for a large portion of the variability observed on intermittent nights. In these conditions, the low-frequency exchange may dominate over the turbulent transfer. In particular, we show that within the canopy most of the exchange of CO2 and H2O happens on temporal scales longer than 100 s. At 80 m, on the other hand, the turbulent fluxes are almost absent in such very stable conditions, suggesting a boundary layer shallower than 80 m. The relationship between TKE and mean winds shows that the stable boundary layer switches from the very stable to the weakly stable regime during intermittent bursts of turbulence. In general, fluxes estimated with long temporal windows that account for the low-frequency effects are more dependent on the stability over a deeper layer above the forest than they are on the stability between the top of the canopy and its interior, suggesting that low-frequency processes are controlled over a deeper layer above the forest.

The Effect of Cutoffs on the Uplift Pressure Beneath the Hydraulic Structures Floor

2018 ◽  
Vol 6 (3) ◽  
pp. 20-28
Author(s):  
Faisal Al Tabatabaie ◽  
Dhabia Sabeeh Al Waily
Keyword(s):  
Potential Energy ◽  
Hydraulic Structure ◽  
Hydraulic Structures ◽  
Outer Face ◽  
Analogue Model ◽  
Electrical Analogue ◽  
Uplift Pressure ◽  
Different Depths ◽  
The Stability ◽  
Critical Sections

The use of cutoffs underneath the hydraulic structures is considered a safe solution to ensure the stability of hydraulic structure against uplift pressure and piping phenomenon in addition to the sliding and overturning forces of the water. These cutoffs are used at critical sections underneath the floor of hydraulic structure to substitute with their depths the horizontal lengths of the creep line of the hydraulic structure base. In this paper, the experimental method- by using electrical analogue model- was carried out to plot the flow net and study the efficiency of the front and rear faces of the cutoffs for dissipating the potential energy of the percolating water underneath the floor of hydraulic structure. An electrical analogue model which was used in this study consists of twenty five models with different depths of upstream and downstream cutoffs. After plotting the flow net for all models, it is concluded that the efficiency of the inner sides are less than that of the outer sides which were investigated before in this topic of this work that both faces reduction values in the uplift pressure are considered the same, where the efficiency of the outer face of upstream cutoff is (70.35) % and for the inner face is (29.64)%, while for the downstream cutoff the efficiency for the outer face is (76.21)% and for the inner face is (23.79)% .

The Effect of Longitudinal Core Flow on Trailing Vortex Stability

2014 ◽  
Author(s):  
Amir Allaf-Akbari ◽  
A. Gordon L. Holloway ◽  
Joseph Hall
Keyword(s):  
Experimental Study ◽  
Velocity Field ◽  
Kinetic Energy ◽  
Vortex Core ◽  
Vortex Generator ◽  
Core Flow ◽  
Vortex Stability ◽  
Vorticity Distribution ◽  
Air Jet ◽  
Jet Velocities

The current experimental study investigates the effect of longitudinal core flow on the formation and structure of a trailing vortex. The vortex is generated using four airfoils connected to a central hub through which a jet flow is added to the vortex core. Time averaged vorticity, circumferential velocity, and turbulent kinetic energy are studied. The statistics of vortex wandering are identified and corrections applied to the vorticity distribution. The vortex generator used in this study was built on the basis of the design described by Beninati et al. [1]. It uses four NACA0012 airfoils connected to a central hub. The wings orientation can be adjusted such that each contributes to a strong trailing vortex on the center of the test section. The vortex generator also had the capability to deliver an air jet directed longitudinally through a hole in the hub at the joint of the airfoils. Tests were done without the jet and with the air jet at jet velocities of 10 and 20 m/s. Planar PIV was used to measure the velocity field in the vicinity of the vortex core. The measurements were taken at 3 chords behind the vortex generator.

Sign in / Sign up

Export Citation Format

Share Document