scholarly journals The effect of coherent stirring on the advection–condensation of water vapour

2017 ◽  
Vol 473 (2202) ◽  
pp. 20170196 ◽  
Author(s):  
Yue-Kin Tsang ◽  
Jacques Vanneste
Keyword(s):  
Water Vapour ◽  
Large Scale ◽  
Passive Scalar ◽  
Hadley Cell ◽  
Moisture Distribution ◽  
Specific Humidity ◽  
Initial Time ◽  
Small Scale ◽  
Kinematic Models ◽  
Scale Turbulence

Atmospheric water vapour is an essential ingredient of weather and climate. The key features of its distribution can be represented by kinematic models which treat it as a passive scalar advected by a prescribed flow and reacting through condensation. Condensation acts as a sink that maintains specific humidity below a prescribed, space-dependent saturation value. To investigate how the interplay between large-scale advection, small-scale turbulence and condensation controls moisture distribution, we develop simple kinematic models which combine a single circulating flow with a Brownian-motion representation of turbulence. We first study the drying mechanism of a water-vapour anomaly released inside a vortex at an initial time. Next, we consider a cellular flow with a moisture source at a boundary. The statistically steady state attained shows features reminiscent of the Hadley cell such as boundary layers, a region of intense precipitation and a relative humidity minimum. Explicit results provide a detailed characterization of these features in the limit of strong flow.

scholarly journals Role of large-scale advection and small-scale turbulence on vertical migration of gyrotactic swimmers

2019 ◽  
Vol 4 (12) ◽  
Author(s):  
C. Marchioli ◽  
H. Bhatia ◽  
G. Sardina ◽  
L. Brandt ◽  
A. Soldati
Keyword(s):  
Vertical Migration ◽  
Large Scale ◽  
Small Scale ◽  
Scale Turbulence

Modeling an Enclosed, Turbulent Reacting Methane Jet With the Premixed Conditional Moment Closure Method

2013 ◽  
Author(s):  
Scott Martin ◽  
Aleksandar Jemcov ◽  
Björn de Ruijter
Keyword(s):  
Turbulent Combustion ◽  
Large Scale ◽  
Reaction Rates ◽  
Moment Closure ◽  
Scalar Dissipation ◽  
Small Scale ◽  
Conditional Moment ◽  
Progress Variable ◽  
Conditional Moment Closure ◽  
Scale Turbulence

Here the premixed Conditional Moment Closure (CMC) method is used to model the recent PIV and Raman turbulent, enclosed reacting methane jet data from DLR Stuttgart [1]. The experimental data has a rectangular test section at atmospheric pressure and temperature with a single inlet jet. A jet velocity of 90 m/s is used with an adiabatic flame temperature of 2,064 K. Contours of major species, temperature and velocities along with velocity rms values are provided. The conditional moment closure model has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes [2]. The simplified CMC model used here falls into the class of table lookup turbulent combustion models where the chemical kinetics are solved offline over a range of conditions and stored in a table that is accessed by the CFD code. Most table lookup models are based on the laminar 1-D flamelet equations, which assume the small scale turbulence does not affect the reaction rates, only the large scale turbulence has an effect on the reaction rates. The CMC model is derived from first principles to account for the effects of small scale turbulence on the reaction rates, as well as the effects of the large scale mixing, making it more versatile than other models. This is accomplished by conditioning the scalars with the reaction progress variable. By conditioning the scalars and accounting for the small scale mixing, the effects of turbulent fluctuations of the temperature on the reaction rates are more accurately modeled. The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. The original premixed CMC model used a constant value of scalar dissipation, here the scalar dissipation is conditioned by the reaction progress variable. The steady RANS 3-D version of the open source CFD code OpenFOAM is used. Velocity, temperature and species are compared to the experimental data. Once validated, this CFD turbulent combustion model will have great utility for designing lean premixed gas turbine combustors.

A Novel Turbulent Aggregation Device for Flue Gas

2014 ◽  
Vol 955-959 ◽  
pp. 2425-2429 ◽  
Author(s):  
Yun Fei Li ◽  
Jian Guo Yang ◽  
Yan Yan Wang ◽  
Xiao Guo Wang
Keyword(s):  
Size Distribution ◽  
Flue Gas ◽  
Large Scale ◽  
Balance Model ◽  
Small Scale ◽  
Multiphase Model ◽  
Specific Performance ◽  
Particles Size Distribution ◽  
Scale Turbulence ◽  
Eulerian Multiphase Model

The purpose of this study is to construct a turbulent aggregation device which has specific performance for fine particle aggregation in flue gas. The device consists of two cylindrical pipes and an array of vanes. The pipes extending fully and normal to the gas stream induce large scale turbulence in the form of vortices, while the vanes downstream a certain distance from the pipes induce small one. The process of turbulent aggregation was numerically simulated by coupling the Eulerian multiphase model and population balance model together with a proposed aggregation kernel function taking the size and inertia of particles into account, and based on data of particles’ size distribution measured from the flue of one power plant. The results show that the large scale turbulence generated by pipes favours the aggregation of smaller particles (smaller than 1μm) notably, while the small scale turbulence benefits the aggregation of bigger particles (larger than 1μm) notably and enhances the uniformity of particle size distribution among different particle groups.

scholarly journals An overview of the effect of large-scale inhomogeneities on small-scale turbulence

2002 ◽  
Vol 14 (7) ◽  
pp. 2475 ◽  
Author(s):  
L. Danaila ◽  
F. Anselmet ◽  
R. A. Antonia
Keyword(s):  
Large Scale ◽  
Small Scale ◽  
Scale Turbulence

scholarly journals Effect of Turbulence on Emerging Magnetic Flux Tubes in the Convection Zone

1990 ◽  
Vol 142 ◽  
pp. 60-61
Author(s):  
Sydney D'Silva ◽  
Arnab Rai Choudhuri
Keyword(s):  
Magnetic Flux ◽  
Coriolis Force ◽  
Large Scale ◽  
Convection Zone ◽  
Rotation Axis ◽  
Giant Cells ◽  
Magnetic Flux Tube ◽  
Small Scale ◽  
Flux Tubes ◽  
Scale Turbulence

Working under the hypothesis that magnetic flux in the sun is generated at the bottom of the convection zone, Choudhuri and Gilman (1987; Astrophys. J. 316, 788) found that a magnetic flux tube symmetric around the rotation axis, when released at the bottom of the convection zone, gets deflected by the Coriolis force and tends to move parallel to the rotation axis as it rises in the convection zone. As a result, all the flux emerges at rather high latitudes and the flux observed at the typical sunspot latitudes remains unexplained. Choudhuri(1989; Solar Physics, in press) finds that non-axisymmetric perturbations too cannot subdue the Coriolis force. In this paper, we no longer treat the convection zone to be passive as in the previous papers, but we consider the role of turbulence in the convection zone in inhibiting the Coriolis force. The interaction of the flux tubes with the turbulence is treated in a phenomenological way as follows: (1) Large scale turbulence on the scale of giant cells can physically drag the tubes outwards, thus pulling the flux towards lower latitudes by dominating over the Coriolis force. (2) Small scale turbulence of the size of the tubes can exchange angular momentum with the tube, thus suppressing the growth of the Coriolis force and making the tubes emerge at lower latitudes. Numerical simulations show that the giant cells can drag the tubes and make them emerge at lower latitudes only if the velocities within the giant cells are unrealistically large or if the radii of the flux tubes are as small as 10 km. However, small scale turbulence can successfully suppress the growth of the Coriolis force if the tubes have radii smaller than about 300 km which may not be unreasonable. Such flux tubes can then emerge at low latitudes where sunspots are seen.

A new model of shoaling and breaking waves. Part 2. Run-up and two-dimensional waves

2019 ◽  
Vol 867 ◽  
pp. 146-194 ◽  
Author(s):  
G. L. Richard ◽  
A. Duran ◽  
B. Fabrèges
Keyword(s):  
Large Scale ◽  
Turbulent Viscosity ◽  
Breaking Waves ◽  
Small Scale ◽  
Two Dimensional ◽  
Numerical Resolution ◽  
Wide Range ◽  
Scale Turbulence ◽  
Run Up ◽  
Averaged Model

We derive a two-dimensional depth-averaged model for coastal waves with both dispersive and dissipative effects. A tensor quantity called enstrophy models the subdepth large-scale turbulence, including its anisotropic character, and is a source of vorticity of the average flow. The small-scale turbulence is modelled through a turbulent-viscosity hypothesis. This fully nonlinear model has equivalent dispersive properties to the Green–Naghdi equations and is treated, both for the optimization of these properties and for the numerical resolution, with the same techniques which are used for the Green–Naghdi system. The model equations are solved with a discontinuous Galerkin discretization based on a decoupling between the hyperbolic and non-hydrostatic parts of the system. The predictions of the model are compared to experimental data in a wide range of physical conditions. Simulations were run in one-dimensional and two-dimensional cases, including run-up and run-down on beaches, non-trivial topographies, wave trains over a bar or propagation around an island or a reef. A very good agreement is reached in every cases, validating the predictive empirical laws for the parameters of the model. These comparisons confirm the efficiency of the present strategy, highlighting the enstrophy as a robust and reliable tool to describe wave breaking even in a two-dimensional context. Compared with existing depth-averaged models, this approach is numerically robust and adds more physical effects without significant increase in numerical complexity.

Modeling the Impact of Convective Entrainment on the Tropical Tropopause

2006 ◽  
Vol 63 (3) ◽  
pp. 1013-1027 ◽  
Author(s):  
F. J. Robinson ◽  
S. C. Sherwood
Keyword(s):  
Heat Flux ◽  
Large Scale ◽  
Small Scale ◽  
Entrainment Rate ◽  
Subgrid Scale ◽  
Turbulence Parameterization ◽  
Tropical Tropopause ◽  
Scale Turbulence ◽  
Cold Point ◽  
The Impact

Abstract Simulations with the Weather Research and Forecasting (WRF) cloud-resolving model of deep moist convective events reveal net cooling near the tropopause (∼15–18 km above ground), caused by a combination of large-scale ascent and small-scale cooling by the irreversible mixing of turbulent eddies overshooting their level of neutral buoyancy. The turbulent cooling occurred at all CAPE values investigated (local peak values ranging from 1900 to 3500 J kg−1) and was robust to grid resolution, subgrid-scale turbulence parameterization, horizontal domain size, model dimension, and treatment of ice microphysics. The ratio of the maximum downward heat flux in the tropopause to the maximum tropospheric upward heat flux was close to 0.1. This value was independent of CAPE but was affected by changes in microphysics or subgrid-scale turbulence parameterization. The convective cooling peaked roughly 1 km above the cold point in the background input sounding and the mean cloud- and (turbulent kinetic energy) TKE-top heights, which were all near 16.5 km above ground. It was associated with turbulent entrainment of stratospheric air from as high as 18.25 km into the troposphere. Typical cooling in the experiments was of order 1 K during convective events that produced order 10 mm of precipitation, which implied a significant contribution to the tropopause energy budget. Given the sharp concentration gradients and long residence times near the cold point, even such a small entrainment rate is likely consequential for the transport and ambient distribution of trace gases such as water vapor and ozone, and probably helps to explain the gradual increase of ozone typically observed below the tropical tropopause.

Triadic scale interactions in a turbulent boundary layer

2015 ◽  
Vol 767 ◽  
Author(s):  
Subrahmanyam Duvvuri ◽  
Beverley J. McKeon
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Small Scale ◽  
Velocity Signal ◽  
Small Scales ◽  
Amplitude Modulation Coefficient ◽  
Scale Turbulence ◽  
Scale Motion ◽  
Phase Relationships

AbstractA formal relationship between the skewness and the correlation coefficient of large and small scales, termed the amplitude modulation coefficient, is established for a general statistically stationary signal and is analysed in the context of a turbulent velocity signal. Both the quantities are seen to be measures of phase in triadically consistent interactions between scales of turbulence. The naturally existing phase relationships between large and small scales in a turbulent boundary layer are then manipulated by exciting a synthetic large-scale motion in the flow using a spatially impulsive dynamic wall roughness perturbation. The synthetic scale is seen to alter the phase relationships, or the degree of modulation, in a quasi-deterministic manner by exhibiting a phase-organizing influence on the small scales. The results presented provide encouragement for the development of a practical framework for favourable manipulation of energetic small-scale turbulence through large-scale inputs in a wall-bounded turbulent flow.

Some specific features of atmospheric tubulence

1962 ◽  
Vol 13 (1) ◽  
pp. 77-81 ◽  
Author(s):  
A. M. Oboukhov
Keyword(s):  
Atmospheric Turbulence ◽  
Large Scale ◽  
Three Dimensional ◽  
Wind Tunnels ◽  
Small Scale ◽  
Horizontal Scale ◽  
Rough Approximation ◽  
External Conditions ◽  
Scale Turbulence

The spectrum of atmospheric turbulence is very broad by comparison with spectra in wind tunnels. We introduce the notion of small-scale and large-scale turbulence. Small-scale turbulence consists of a set of disturbances, the scales of which do not exceed the distance to the wall and for which the hypothesis of three-dimensional isotropy is valid in a certain rough approximation. Large-scale turbulence is essentially anisotropic; the horizontal scale in the atmosphere is much larger than the vertical one, the latter being confined to a certain characteristic height H. The horizontal scale varies widely according to the external conditions and characteristics of the medium.

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